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    Subject[tip: locking/core] futex: Move to kernel/futex/
    The following commit has been merged into the locking/core branch of tip:

    Commit-ID: 77e52ae35463521041906c510fe580d15663bb93
    Gitweb: https://git.kernel.org/tip/77e52ae35463521041906c510fe580d15663bb93
    Author: Peter Zijlstra <peterz@infradead.org>
    AuthorDate: Thu, 23 Sep 2021 14:10:50 -03:00
    Committer: Peter Zijlstra <peterz@infradead.org>
    CommitterDate: Thu, 07 Oct 2021 13:51:07 +02:00

    futex: Move to kernel/futex/

    In preparation for splitup..

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Suggested-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: André Almeida <andrealmeid@collabora.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Reviewed-by: André Almeida <andrealmeid@collabora.com>
    Link: https://lore.kernel.org/r/20210923171111.300673-2-andrealmeid@collabora.com
    ---
    MAINTAINERS | 2 +-
    kernel/Makefile | 2 +-
    kernel/futex.c | 4272 +----------------------------------------
    kernel/futex/Makefile | 3 +-
    kernel/futex/core.c | 4272 ++++++++++++++++++++++++++++++++++++++++-
    5 files changed, 4277 insertions(+), 4274 deletions(-)
    delete mode 100644 kernel/futex.c
    create mode 100644 kernel/futex/Makefile
    create mode 100644 kernel/futex/core.c

    diff --git a/MAINTAINERS b/MAINTAINERS
    index eeb4c70..b3094cb 100644
    --- a/MAINTAINERS
    +++ b/MAINTAINERS
    @@ -7725,7 +7725,7 @@ F: Documentation/locking/*futex*
    F: include/asm-generic/futex.h
    F: include/linux/futex.h
    F: include/uapi/linux/futex.h
    -F: kernel/futex.c
    +F: kernel/futex/*
    F: tools/perf/bench/futex*
    F: tools/testing/selftests/futex/

    diff --git a/kernel/Makefile b/kernel/Makefile
    index 4df609b..3f6ab5d 100644
    --- a/kernel/Makefile
    +++ b/kernel/Makefile
    @@ -59,7 +59,7 @@ obj-$(CONFIG_FREEZER) += freezer.o
    obj-$(CONFIG_PROFILING) += profile.o
    obj-$(CONFIG_STACKTRACE) += stacktrace.o
    obj-y += time/
    -obj-$(CONFIG_FUTEX) += futex.o
    +obj-$(CONFIG_FUTEX) += futex/
    obj-$(CONFIG_GENERIC_ISA_DMA) += dma.o
    obj-$(CONFIG_SMP) += smp.o
    ifneq ($(CONFIG_SMP),y)
    diff --git a/kernel/futex.c b/kernel/futex.c
    deleted file mode 100644
    index c15ad27..0000000
    --- a/kernel/futex.c
    +++ /dev/null
    @@ -1,4272 +0,0 @@
    -// SPDX-License-Identifier: GPL-2.0-or-later
    -/*
    - * Fast Userspace Mutexes (which I call "Futexes!").
    - * (C) Rusty Russell, IBM 2002
    - *
    - * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
    - * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
    - *
    - * Removed page pinning, fix privately mapped COW pages and other cleanups
    - * (C) Copyright 2003, 2004 Jamie Lokier
    - *
    - * Robust futex support started by Ingo Molnar
    - * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
    - * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
    - *
    - * PI-futex support started by Ingo Molnar and Thomas Gleixner
    - * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
    - * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
    - *
    - * PRIVATE futexes by Eric Dumazet
    - * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
    - *
    - * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
    - * Copyright (C) IBM Corporation, 2009
    - * Thanks to Thomas Gleixner for conceptual design and careful reviews.
    - *
    - * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
    - * enough at me, Linus for the original (flawed) idea, Matthew
    - * Kirkwood for proof-of-concept implementation.
    - *
    - * "The futexes are also cursed."
    - * "But they come in a choice of three flavours!"
    - */
    -#include <linux/compat.h>
    -#include <linux/jhash.h>
    -#include <linux/pagemap.h>
    -#include <linux/syscalls.h>
    -#include <linux/freezer.h>
    -#include <linux/memblock.h>
    -#include <linux/fault-inject.h>
    -#include <linux/time_namespace.h>
    -
    -#include <asm/futex.h>
    -
    -#include "locking/rtmutex_common.h"
    -
    -/*
    - * READ this before attempting to hack on futexes!
    - *
    - * Basic futex operation and ordering guarantees
    - * =============================================
    - *
    - * The waiter reads the futex value in user space and calls
    - * futex_wait(). This function computes the hash bucket and acquires
    - * the hash bucket lock. After that it reads the futex user space value
    - * again and verifies that the data has not changed. If it has not changed
    - * it enqueues itself into the hash bucket, releases the hash bucket lock
    - * and schedules.
    - *
    - * The waker side modifies the user space value of the futex and calls
    - * futex_wake(). This function computes the hash bucket and acquires the
    - * hash bucket lock. Then it looks for waiters on that futex in the hash
    - * bucket and wakes them.
    - *
    - * In futex wake up scenarios where no tasks are blocked on a futex, taking
    - * the hb spinlock can be avoided and simply return. In order for this
    - * optimization to work, ordering guarantees must exist so that the waiter
    - * being added to the list is acknowledged when the list is concurrently being
    - * checked by the waker, avoiding scenarios like the following:
    - *
    - * CPU 0 CPU 1
    - * val = *futex;
    - * sys_futex(WAIT, futex, val);
    - * futex_wait(futex, val);
    - * uval = *futex;
    - * *futex = newval;
    - * sys_futex(WAKE, futex);
    - * futex_wake(futex);
    - * if (queue_empty())
    - * return;
    - * if (uval == val)
    - * lock(hash_bucket(futex));
    - * queue();
    - * unlock(hash_bucket(futex));
    - * schedule();
    - *
    - * This would cause the waiter on CPU 0 to wait forever because it
    - * missed the transition of the user space value from val to newval
    - * and the waker did not find the waiter in the hash bucket queue.
    - *
    - * The correct serialization ensures that a waiter either observes
    - * the changed user space value before blocking or is woken by a
    - * concurrent waker:
    - *
    - * CPU 0 CPU 1
    - * val = *futex;
    - * sys_futex(WAIT, futex, val);
    - * futex_wait(futex, val);
    - *
    - * waiters++; (a)
    - * smp_mb(); (A) <-- paired with -.
    - * |
    - * lock(hash_bucket(futex)); |
    - * |
    - * uval = *futex; |
    - * | *futex = newval;
    - * | sys_futex(WAKE, futex);
    - * | futex_wake(futex);
    - * |
    - * `--------> smp_mb(); (B)
    - * if (uval == val)
    - * queue();
    - * unlock(hash_bucket(futex));
    - * schedule(); if (waiters)
    - * lock(hash_bucket(futex));
    - * else wake_waiters(futex);
    - * waiters--; (b) unlock(hash_bucket(futex));
    - *
    - * Where (A) orders the waiters increment and the futex value read through
    - * atomic operations (see hb_waiters_inc) and where (B) orders the write
    - * to futex and the waiters read (see hb_waiters_pending()).
    - *
    - * This yields the following case (where X:=waiters, Y:=futex):
    - *
    - * X = Y = 0
    - *
    - * w[X]=1 w[Y]=1
    - * MB MB
    - * r[Y]=y r[X]=x
    - *
    - * Which guarantees that x==0 && y==0 is impossible; which translates back into
    - * the guarantee that we cannot both miss the futex variable change and the
    - * enqueue.
    - *
    - * Note that a new waiter is accounted for in (a) even when it is possible that
    - * the wait call can return error, in which case we backtrack from it in (b).
    - * Refer to the comment in queue_lock().
    - *
    - * Similarly, in order to account for waiters being requeued on another
    - * address we always increment the waiters for the destination bucket before
    - * acquiring the lock. It then decrements them again after releasing it -
    - * the code that actually moves the futex(es) between hash buckets (requeue_futex)
    - * will do the additional required waiter count housekeeping. This is done for
    - * double_lock_hb() and double_unlock_hb(), respectively.
    - */
    -
    -#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
    -#define futex_cmpxchg_enabled 1
    -#else
    -static int __read_mostly futex_cmpxchg_enabled;
    -#endif
    -
    -/*
    - * Futex flags used to encode options to functions and preserve them across
    - * restarts.
    - */
    -#ifdef CONFIG_MMU
    -# define FLAGS_SHARED 0x01
    -#else
    -/*
    - * NOMMU does not have per process address space. Let the compiler optimize
    - * code away.
    - */
    -# define FLAGS_SHARED 0x00
    -#endif
    -#define FLAGS_CLOCKRT 0x02
    -#define FLAGS_HAS_TIMEOUT 0x04
    -
    -/*
    - * Priority Inheritance state:
    - */
    -struct futex_pi_state {
    - /*
    - * list of 'owned' pi_state instances - these have to be
    - * cleaned up in do_exit() if the task exits prematurely:
    - */
    - struct list_head list;
    -
    - /*
    - * The PI object:
    - */
    - struct rt_mutex_base pi_mutex;
    -
    - struct task_struct *owner;
    - refcount_t refcount;
    -
    - union futex_key key;
    -} __randomize_layout;
    -
    -/**
    - * struct futex_q - The hashed futex queue entry, one per waiting task
    - * @list: priority-sorted list of tasks waiting on this futex
    - * @task: the task waiting on the futex
    - * @lock_ptr: the hash bucket lock
    - * @key: the key the futex is hashed on
    - * @pi_state: optional priority inheritance state
    - * @rt_waiter: rt_waiter storage for use with requeue_pi
    - * @requeue_pi_key: the requeue_pi target futex key
    - * @bitset: bitset for the optional bitmasked wakeup
    - * @requeue_state: State field for futex_requeue_pi()
    - * @requeue_wait: RCU wait for futex_requeue_pi() (RT only)
    - *
    - * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
    - * we can wake only the relevant ones (hashed queues may be shared).
    - *
    - * A futex_q has a woken state, just like tasks have TASK_RUNNING.
    - * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
    - * The order of wakeup is always to make the first condition true, then
    - * the second.
    - *
    - * PI futexes are typically woken before they are removed from the hash list via
    - * the rt_mutex code. See unqueue_me_pi().
    - */
    -struct futex_q {
    - struct plist_node list;
    -
    - struct task_struct *task;
    - spinlock_t *lock_ptr;
    - union futex_key key;
    - struct futex_pi_state *pi_state;
    - struct rt_mutex_waiter *rt_waiter;
    - union futex_key *requeue_pi_key;
    - u32 bitset;
    - atomic_t requeue_state;
    -#ifdef CONFIG_PREEMPT_RT
    - struct rcuwait requeue_wait;
    -#endif
    -} __randomize_layout;
    -
    -/*
    - * On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an
    - * underlying rtmutex. The task which is about to be requeued could have
    - * just woken up (timeout, signal). After the wake up the task has to
    - * acquire hash bucket lock, which is held by the requeue code. As a task
    - * can only be blocked on _ONE_ rtmutex at a time, the proxy lock blocking
    - * and the hash bucket lock blocking would collide and corrupt state.
    - *
    - * On !PREEMPT_RT this is not a problem and everything could be serialized
    - * on hash bucket lock, but aside of having the benefit of common code,
    - * this allows to avoid doing the requeue when the task is already on the
    - * way out and taking the hash bucket lock of the original uaddr1 when the
    - * requeue has been completed.
    - *
    - * The following state transitions are valid:
    - *
    - * On the waiter side:
    - * Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_IGNORE
    - * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_WAIT
    - *
    - * On the requeue side:
    - * Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_INPROGRESS
    - * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_DONE/LOCKED
    - * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_NONE (requeue failed)
    - * Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_DONE/LOCKED
    - * Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_IGNORE (requeue failed)
    - *
    - * The requeue side ignores a waiter with state Q_REQUEUE_PI_IGNORE as this
    - * signals that the waiter is already on the way out. It also means that
    - * the waiter is still on the 'wait' futex, i.e. uaddr1.
    - *
    - * The waiter side signals early wakeup to the requeue side either through
    - * setting state to Q_REQUEUE_PI_IGNORE or to Q_REQUEUE_PI_WAIT depending
    - * on the current state. In case of Q_REQUEUE_PI_IGNORE it can immediately
    - * proceed to take the hash bucket lock of uaddr1. If it set state to WAIT,
    - * which means the wakeup is interleaving with a requeue in progress it has
    - * to wait for the requeue side to change the state. Either to DONE/LOCKED
    - * or to IGNORE. DONE/LOCKED means the waiter q is now on the uaddr2 futex
    - * and either blocked (DONE) or has acquired it (LOCKED). IGNORE is set by
    - * the requeue side when the requeue attempt failed via deadlock detection
    - * and therefore the waiter q is still on the uaddr1 futex.
    - */
    -enum {
    - Q_REQUEUE_PI_NONE = 0,
    - Q_REQUEUE_PI_IGNORE,
    - Q_REQUEUE_PI_IN_PROGRESS,
    - Q_REQUEUE_PI_WAIT,
    - Q_REQUEUE_PI_DONE,
    - Q_REQUEUE_PI_LOCKED,
    -};
    -
    -static const struct futex_q futex_q_init = {
    - /* list gets initialized in queue_me()*/
    - .key = FUTEX_KEY_INIT,
    - .bitset = FUTEX_BITSET_MATCH_ANY,
    - .requeue_state = ATOMIC_INIT(Q_REQUEUE_PI_NONE),
    -};
    -
    -/*
    - * Hash buckets are shared by all the futex_keys that hash to the same
    - * location. Each key may have multiple futex_q structures, one for each task
    - * waiting on a futex.
    - */
    -struct futex_hash_bucket {
    - atomic_t waiters;
    - spinlock_t lock;
    - struct plist_head chain;
    -} ____cacheline_aligned_in_smp;
    -
    -/*
    - * The base of the bucket array and its size are always used together
    - * (after initialization only in hash_futex()), so ensure that they
    - * reside in the same cacheline.
    - */
    -static struct {
    - struct futex_hash_bucket *queues;
    - unsigned long hashsize;
    -} __futex_data __read_mostly __aligned(2*sizeof(long));
    -#define futex_queues (__futex_data.queues)
    -#define futex_hashsize (__futex_data.hashsize)
    -
    -
    -/*
    - * Fault injections for futexes.
    - */
    -#ifdef CONFIG_FAIL_FUTEX
    -
    -static struct {
    - struct fault_attr attr;
    -
    - bool ignore_private;
    -} fail_futex = {
    - .attr = FAULT_ATTR_INITIALIZER,
    - .ignore_private = false,
    -};
    -
    -static int __init setup_fail_futex(char *str)
    -{
    - return setup_fault_attr(&fail_futex.attr, str);
    -}
    -__setup("fail_futex=", setup_fail_futex);
    -
    -static bool should_fail_futex(bool fshared)
    -{
    - if (fail_futex.ignore_private && !fshared)
    - return false;
    -
    - return should_fail(&fail_futex.attr, 1);
    -}
    -
    -#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
    -
    -static int __init fail_futex_debugfs(void)
    -{
    - umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
    - struct dentry *dir;
    -
    - dir = fault_create_debugfs_attr("fail_futex", NULL,
    - &fail_futex.attr);
    - if (IS_ERR(dir))
    - return PTR_ERR(dir);
    -
    - debugfs_create_bool("ignore-private", mode, dir,
    - &fail_futex.ignore_private);
    - return 0;
    -}
    -
    -late_initcall(fail_futex_debugfs);
    -
    -#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
    -
    -#else
    -static inline bool should_fail_futex(bool fshared)
    -{
    - return false;
    -}
    -#endif /* CONFIG_FAIL_FUTEX */
    -
    -#ifdef CONFIG_COMPAT
    -static void compat_exit_robust_list(struct task_struct *curr);
    -#endif
    -
    -/*
    - * Reflects a new waiter being added to the waitqueue.
    - */
    -static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
    -{
    -#ifdef CONFIG_SMP
    - atomic_inc(&hb->waiters);
    - /*
    - * Full barrier (A), see the ordering comment above.
    - */
    - smp_mb__after_atomic();
    -#endif
    -}
    -
    -/*
    - * Reflects a waiter being removed from the waitqueue by wakeup
    - * paths.
    - */
    -static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
    -{
    -#ifdef CONFIG_SMP
    - atomic_dec(&hb->waiters);
    -#endif
    -}
    -
    -static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
    -{
    -#ifdef CONFIG_SMP
    - /*
    - * Full barrier (B), see the ordering comment above.
    - */
    - smp_mb();
    - return atomic_read(&hb->waiters);
    -#else
    - return 1;
    -#endif
    -}
    -
    -/**
    - * hash_futex - Return the hash bucket in the global hash
    - * @key: Pointer to the futex key for which the hash is calculated
    - *
    - * We hash on the keys returned from get_futex_key (see below) and return the
    - * corresponding hash bucket in the global hash.
    - */
    -static struct futex_hash_bucket *hash_futex(union futex_key *key)
    -{
    - u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
    - key->both.offset);
    -
    - return &futex_queues[hash & (futex_hashsize - 1)];
    -}
    -
    -
    -/**
    - * match_futex - Check whether two futex keys are equal
    - * @key1: Pointer to key1
    - * @key2: Pointer to key2
    - *
    - * Return 1 if two futex_keys are equal, 0 otherwise.
    - */
    -static inline int match_futex(union futex_key *key1, union futex_key *key2)
    -{
    - return (key1 && key2
    - && key1->both.word == key2->both.word
    - && key1->both.ptr == key2->both.ptr
    - && key1->both.offset == key2->both.offset);
    -}
    -
    -enum futex_access {
    - FUTEX_READ,
    - FUTEX_WRITE
    -};
    -
    -/**
    - * futex_setup_timer - set up the sleeping hrtimer.
    - * @time: ptr to the given timeout value
    - * @timeout: the hrtimer_sleeper structure to be set up
    - * @flags: futex flags
    - * @range_ns: optional range in ns
    - *
    - * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
    - * value given
    - */
    -static inline struct hrtimer_sleeper *
    -futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
    - int flags, u64 range_ns)
    -{
    - if (!time)
    - return NULL;
    -
    - hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
    - CLOCK_REALTIME : CLOCK_MONOTONIC,
    - HRTIMER_MODE_ABS);
    - /*
    - * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
    - * effectively the same as calling hrtimer_set_expires().
    - */
    - hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
    -
    - return timeout;
    -}
    -
    -/*
    - * Generate a machine wide unique identifier for this inode.
    - *
    - * This relies on u64 not wrapping in the life-time of the machine; which with
    - * 1ns resolution means almost 585 years.
    - *
    - * This further relies on the fact that a well formed program will not unmap
    - * the file while it has a (shared) futex waiting on it. This mapping will have
    - * a file reference which pins the mount and inode.
    - *
    - * If for some reason an inode gets evicted and read back in again, it will get
    - * a new sequence number and will _NOT_ match, even though it is the exact same
    - * file.
    - *
    - * It is important that match_futex() will never have a false-positive, esp.
    - * for PI futexes that can mess up the state. The above argues that false-negatives
    - * are only possible for malformed programs.
    - */
    -static u64 get_inode_sequence_number(struct inode *inode)
    -{
    - static atomic64_t i_seq;
    - u64 old;
    -
    - /* Does the inode already have a sequence number? */
    - old = atomic64_read(&inode->i_sequence);
    - if (likely(old))
    - return old;
    -
    - for (;;) {
    - u64 new = atomic64_add_return(1, &i_seq);
    - if (WARN_ON_ONCE(!new))
    - continue;
    -
    - old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
    - if (old)
    - return old;
    - return new;
    - }
    -}
    -
    -/**
    - * get_futex_key() - Get parameters which are the keys for a futex
    - * @uaddr: virtual address of the futex
    - * @fshared: false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED
    - * @key: address where result is stored.
    - * @rw: mapping needs to be read/write (values: FUTEX_READ,
    - * FUTEX_WRITE)
    - *
    - * Return: a negative error code or 0
    - *
    - * The key words are stored in @key on success.
    - *
    - * For shared mappings (when @fshared), the key is:
    - *
    - * ( inode->i_sequence, page->index, offset_within_page )
    - *
    - * [ also see get_inode_sequence_number() ]
    - *
    - * For private mappings (or when !@fshared), the key is:
    - *
    - * ( current->mm, address, 0 )
    - *
    - * This allows (cross process, where applicable) identification of the futex
    - * without keeping the page pinned for the duration of the FUTEX_WAIT.
    - *
    - * lock_page() might sleep, the caller should not hold a spinlock.
    - */
    -static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
    - enum futex_access rw)
    -{
    - unsigned long address = (unsigned long)uaddr;
    - struct mm_struct *mm = current->mm;
    - struct page *page, *tail;
    - struct address_space *mapping;
    - int err, ro = 0;
    -
    - /*
    - * The futex address must be "naturally" aligned.
    - */
    - key->both.offset = address % PAGE_SIZE;
    - if (unlikely((address % sizeof(u32)) != 0))
    - return -EINVAL;
    - address -= key->both.offset;
    -
    - if (unlikely(!access_ok(uaddr, sizeof(u32))))
    - return -EFAULT;
    -
    - if (unlikely(should_fail_futex(fshared)))
    - return -EFAULT;
    -
    - /*
    - * PROCESS_PRIVATE futexes are fast.
    - * As the mm cannot disappear under us and the 'key' only needs
    - * virtual address, we dont even have to find the underlying vma.
    - * Note : We do have to check 'uaddr' is a valid user address,
    - * but access_ok() should be faster than find_vma()
    - */
    - if (!fshared) {
    - key->private.mm = mm;
    - key->private.address = address;
    - return 0;
    - }
    -
    -again:
    - /* Ignore any VERIFY_READ mapping (futex common case) */
    - if (unlikely(should_fail_futex(true)))
    - return -EFAULT;
    -
    - err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
    - /*
    - * If write access is not required (eg. FUTEX_WAIT), try
    - * and get read-only access.
    - */
    - if (err == -EFAULT && rw == FUTEX_READ) {
    - err = get_user_pages_fast(address, 1, 0, &page);
    - ro = 1;
    - }
    - if (err < 0)
    - return err;
    - else
    - err = 0;
    -
    - /*
    - * The treatment of mapping from this point on is critical. The page
    - * lock protects many things but in this context the page lock
    - * stabilizes mapping, prevents inode freeing in the shared
    - * file-backed region case and guards against movement to swap cache.
    - *
    - * Strictly speaking the page lock is not needed in all cases being
    - * considered here and page lock forces unnecessarily serialization
    - * From this point on, mapping will be re-verified if necessary and
    - * page lock will be acquired only if it is unavoidable
    - *
    - * Mapping checks require the head page for any compound page so the
    - * head page and mapping is looked up now. For anonymous pages, it
    - * does not matter if the page splits in the future as the key is
    - * based on the address. For filesystem-backed pages, the tail is
    - * required as the index of the page determines the key. For
    - * base pages, there is no tail page and tail == page.
    - */
    - tail = page;
    - page = compound_head(page);
    - mapping = READ_ONCE(page->mapping);
    -
    - /*
    - * If page->mapping is NULL, then it cannot be a PageAnon
    - * page; but it might be the ZERO_PAGE or in the gate area or
    - * in a special mapping (all cases which we are happy to fail);
    - * or it may have been a good file page when get_user_pages_fast
    - * found it, but truncated or holepunched or subjected to
    - * invalidate_complete_page2 before we got the page lock (also
    - * cases which we are happy to fail). And we hold a reference,
    - * so refcount care in invalidate_complete_page's remove_mapping
    - * prevents drop_caches from setting mapping to NULL beneath us.
    - *
    - * The case we do have to guard against is when memory pressure made
    - * shmem_writepage move it from filecache to swapcache beneath us:
    - * an unlikely race, but we do need to retry for page->mapping.
    - */
    - if (unlikely(!mapping)) {
    - int shmem_swizzled;
    -
    - /*
    - * Page lock is required to identify which special case above
    - * applies. If this is really a shmem page then the page lock
    - * will prevent unexpected transitions.
    - */
    - lock_page(page);
    - shmem_swizzled = PageSwapCache(page) || page->mapping;
    - unlock_page(page);
    - put_page(page);
    -
    - if (shmem_swizzled)
    - goto again;
    -
    - return -EFAULT;
    - }
    -
    - /*
    - * Private mappings are handled in a simple way.
    - *
    - * If the futex key is stored on an anonymous page, then the associated
    - * object is the mm which is implicitly pinned by the calling process.
    - *
    - * NOTE: When userspace waits on a MAP_SHARED mapping, even if
    - * it's a read-only handle, it's expected that futexes attach to
    - * the object not the particular process.
    - */
    - if (PageAnon(page)) {
    - /*
    - * A RO anonymous page will never change and thus doesn't make
    - * sense for futex operations.
    - */
    - if (unlikely(should_fail_futex(true)) || ro) {
    - err = -EFAULT;
    - goto out;
    - }
    -
    - key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
    - key->private.mm = mm;
    - key->private.address = address;
    -
    - } else {
    - struct inode *inode;
    -
    - /*
    - * The associated futex object in this case is the inode and
    - * the page->mapping must be traversed. Ordinarily this should
    - * be stabilised under page lock but it's not strictly
    - * necessary in this case as we just want to pin the inode, not
    - * update the radix tree or anything like that.
    - *
    - * The RCU read lock is taken as the inode is finally freed
    - * under RCU. If the mapping still matches expectations then the
    - * mapping->host can be safely accessed as being a valid inode.
    - */
    - rcu_read_lock();
    -
    - if (READ_ONCE(page->mapping) != mapping) {
    - rcu_read_unlock();
    - put_page(page);
    -
    - goto again;
    - }
    -
    - inode = READ_ONCE(mapping->host);
    - if (!inode) {
    - rcu_read_unlock();
    - put_page(page);
    -
    - goto again;
    - }
    -
    - key->both.offset |= FUT_OFF_INODE; /* inode-based key */
    - key->shared.i_seq = get_inode_sequence_number(inode);
    - key->shared.pgoff = page_to_pgoff(tail);
    - rcu_read_unlock();
    - }
    -
    -out:
    - put_page(page);
    - return err;
    -}
    -
    -/**
    - * fault_in_user_writeable() - Fault in user address and verify RW access
    - * @uaddr: pointer to faulting user space address
    - *
    - * Slow path to fixup the fault we just took in the atomic write
    - * access to @uaddr.
    - *
    - * We have no generic implementation of a non-destructive write to the
    - * user address. We know that we faulted in the atomic pagefault
    - * disabled section so we can as well avoid the #PF overhead by
    - * calling get_user_pages() right away.
    - */
    -static int fault_in_user_writeable(u32 __user *uaddr)
    -{
    - struct mm_struct *mm = current->mm;
    - int ret;
    -
    - mmap_read_lock(mm);
    - ret = fixup_user_fault(mm, (unsigned long)uaddr,
    - FAULT_FLAG_WRITE, NULL);
    - mmap_read_unlock(mm);
    -
    - return ret < 0 ? ret : 0;
    -}
    -
    -/**
    - * futex_top_waiter() - Return the highest priority waiter on a futex
    - * @hb: the hash bucket the futex_q's reside in
    - * @key: the futex key (to distinguish it from other futex futex_q's)
    - *
    - * Must be called with the hb lock held.
    - */
    -static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
    - union futex_key *key)
    -{
    - struct futex_q *this;
    -
    - plist_for_each_entry(this, &hb->chain, list) {
    - if (match_futex(&this->key, key))
    - return this;
    - }
    - return NULL;
    -}
    -
    -static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
    - u32 uval, u32 newval)
    -{
    - int ret;
    -
    - pagefault_disable();
    - ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
    - pagefault_enable();
    -
    - return ret;
    -}
    -
    -static int get_futex_value_locked(u32 *dest, u32 __user *from)
    -{
    - int ret;
    -
    - pagefault_disable();
    - ret = __get_user(*dest, from);
    - pagefault_enable();
    -
    - return ret ? -EFAULT : 0;
    -}
    -
    -
    -/*
    - * PI code:
    - */
    -static int refill_pi_state_cache(void)
    -{
    - struct futex_pi_state *pi_state;
    -
    - if (likely(current->pi_state_cache))
    - return 0;
    -
    - pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
    -
    - if (!pi_state)
    - return -ENOMEM;
    -
    - INIT_LIST_HEAD(&pi_state->list);
    - /* pi_mutex gets initialized later */
    - pi_state->owner = NULL;
    - refcount_set(&pi_state->refcount, 1);
    - pi_state->key = FUTEX_KEY_INIT;
    -
    - current->pi_state_cache = pi_state;
    -
    - return 0;
    -}
    -
    -static struct futex_pi_state *alloc_pi_state(void)
    -{
    - struct futex_pi_state *pi_state = current->pi_state_cache;
    -
    - WARN_ON(!pi_state);
    - current->pi_state_cache = NULL;
    -
    - return pi_state;
    -}
    -
    -static void pi_state_update_owner(struct futex_pi_state *pi_state,
    - struct task_struct *new_owner)
    -{
    - struct task_struct *old_owner = pi_state->owner;
    -
    - lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
    -
    - if (old_owner) {
    - raw_spin_lock(&old_owner->pi_lock);
    - WARN_ON(list_empty(&pi_state->list));
    - list_del_init(&pi_state->list);
    - raw_spin_unlock(&old_owner->pi_lock);
    - }
    -
    - if (new_owner) {
    - raw_spin_lock(&new_owner->pi_lock);
    - WARN_ON(!list_empty(&pi_state->list));
    - list_add(&pi_state->list, &new_owner->pi_state_list);
    - pi_state->owner = new_owner;
    - raw_spin_unlock(&new_owner->pi_lock);
    - }
    -}
    -
    -static void get_pi_state(struct futex_pi_state *pi_state)
    -{
    - WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
    -}
    -
    -/*
    - * Drops a reference to the pi_state object and frees or caches it
    - * when the last reference is gone.
    - */
    -static void put_pi_state(struct futex_pi_state *pi_state)
    -{
    - if (!pi_state)
    - return;
    -
    - if (!refcount_dec_and_test(&pi_state->refcount))
    - return;
    -
    - /*
    - * If pi_state->owner is NULL, the owner is most probably dying
    - * and has cleaned up the pi_state already
    - */
    - if (pi_state->owner) {
    - unsigned long flags;
    -
    - raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
    - pi_state_update_owner(pi_state, NULL);
    - rt_mutex_proxy_unlock(&pi_state->pi_mutex);
    - raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
    - }
    -
    - if (current->pi_state_cache) {
    - kfree(pi_state);
    - } else {
    - /*
    - * pi_state->list is already empty.
    - * clear pi_state->owner.
    - * refcount is at 0 - put it back to 1.
    - */
    - pi_state->owner = NULL;
    - refcount_set(&pi_state->refcount, 1);
    - current->pi_state_cache = pi_state;
    - }
    -}
    -
    -#ifdef CONFIG_FUTEX_PI
    -
    -/*
    - * This task is holding PI mutexes at exit time => bad.
    - * Kernel cleans up PI-state, but userspace is likely hosed.
    - * (Robust-futex cleanup is separate and might save the day for userspace.)
    - */
    -static void exit_pi_state_list(struct task_struct *curr)
    -{
    - struct list_head *next, *head = &curr->pi_state_list;
    - struct futex_pi_state *pi_state;
    - struct futex_hash_bucket *hb;
    - union futex_key key = FUTEX_KEY_INIT;
    -
    - if (!futex_cmpxchg_enabled)
    - return;
    - /*
    - * We are a ZOMBIE and nobody can enqueue itself on
    - * pi_state_list anymore, but we have to be careful
    - * versus waiters unqueueing themselves:
    - */
    - raw_spin_lock_irq(&curr->pi_lock);
    - while (!list_empty(head)) {
    - next = head->next;
    - pi_state = list_entry(next, struct futex_pi_state, list);
    - key = pi_state->key;
    - hb = hash_futex(&key);
    -
    - /*
    - * We can race against put_pi_state() removing itself from the
    - * list (a waiter going away). put_pi_state() will first
    - * decrement the reference count and then modify the list, so
    - * its possible to see the list entry but fail this reference
    - * acquire.
    - *
    - * In that case; drop the locks to let put_pi_state() make
    - * progress and retry the loop.
    - */
    - if (!refcount_inc_not_zero(&pi_state->refcount)) {
    - raw_spin_unlock_irq(&curr->pi_lock);
    - cpu_relax();
    - raw_spin_lock_irq(&curr->pi_lock);
    - continue;
    - }
    - raw_spin_unlock_irq(&curr->pi_lock);
    -
    - spin_lock(&hb->lock);
    - raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    - raw_spin_lock(&curr->pi_lock);
    - /*
    - * We dropped the pi-lock, so re-check whether this
    - * task still owns the PI-state:
    - */
    - if (head->next != next) {
    - /* retain curr->pi_lock for the loop invariant */
    - raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
    - spin_unlock(&hb->lock);
    - put_pi_state(pi_state);
    - continue;
    - }
    -
    - WARN_ON(pi_state->owner != curr);
    - WARN_ON(list_empty(&pi_state->list));
    - list_del_init(&pi_state->list);
    - pi_state->owner = NULL;
    -
    - raw_spin_unlock(&curr->pi_lock);
    - raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    - spin_unlock(&hb->lock);
    -
    - rt_mutex_futex_unlock(&pi_state->pi_mutex);
    - put_pi_state(pi_state);
    -
    - raw_spin_lock_irq(&curr->pi_lock);
    - }
    - raw_spin_unlock_irq(&curr->pi_lock);
    -}
    -#else
    -static inline void exit_pi_state_list(struct task_struct *curr) { }
    -#endif
    -
    -/*
    - * We need to check the following states:
    - *
    - * Waiter | pi_state | pi->owner | uTID | uODIED | ?
    - *
    - * [1] NULL | --- | --- | 0 | 0/1 | Valid
    - * [2] NULL | --- | --- | >0 | 0/1 | Valid
    - *
    - * [3] Found | NULL | -- | Any | 0/1 | Invalid
    - *
    - * [4] Found | Found | NULL | 0 | 1 | Valid
    - * [5] Found | Found | NULL | >0 | 1 | Invalid
    - *
    - * [6] Found | Found | task | 0 | 1 | Valid
    - *
    - * [7] Found | Found | NULL | Any | 0 | Invalid
    - *
    - * [8] Found | Found | task | ==taskTID | 0/1 | Valid
    - * [9] Found | Found | task | 0 | 0 | Invalid
    - * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
    - *
    - * [1] Indicates that the kernel can acquire the futex atomically. We
    - * came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
    - *
    - * [2] Valid, if TID does not belong to a kernel thread. If no matching
    - * thread is found then it indicates that the owner TID has died.
    - *
    - * [3] Invalid. The waiter is queued on a non PI futex
    - *
    - * [4] Valid state after exit_robust_list(), which sets the user space
    - * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
    - *
    - * [5] The user space value got manipulated between exit_robust_list()
    - * and exit_pi_state_list()
    - *
    - * [6] Valid state after exit_pi_state_list() which sets the new owner in
    - * the pi_state but cannot access the user space value.
    - *
    - * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
    - *
    - * [8] Owner and user space value match
    - *
    - * [9] There is no transient state which sets the user space TID to 0
    - * except exit_robust_list(), but this is indicated by the
    - * FUTEX_OWNER_DIED bit. See [4]
    - *
    - * [10] There is no transient state which leaves owner and user space
    - * TID out of sync. Except one error case where the kernel is denied
    - * write access to the user address, see fixup_pi_state_owner().
    - *
    - *
    - * Serialization and lifetime rules:
    - *
    - * hb->lock:
    - *
    - * hb -> futex_q, relation
    - * futex_q -> pi_state, relation
    - *
    - * (cannot be raw because hb can contain arbitrary amount
    - * of futex_q's)
    - *
    - * pi_mutex->wait_lock:
    - *
    - * {uval, pi_state}
    - *
    - * (and pi_mutex 'obviously')
    - *
    - * p->pi_lock:
    - *
    - * p->pi_state_list -> pi_state->list, relation
    - * pi_mutex->owner -> pi_state->owner, relation
    - *
    - * pi_state->refcount:
    - *
    - * pi_state lifetime
    - *
    - *
    - * Lock order:
    - *
    - * hb->lock
    - * pi_mutex->wait_lock
    - * p->pi_lock
    - *
    - */
    -
    -/*
    - * Validate that the existing waiter has a pi_state and sanity check
    - * the pi_state against the user space value. If correct, attach to
    - * it.
    - */
    -static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
    - struct futex_pi_state *pi_state,
    - struct futex_pi_state **ps)
    -{
    - pid_t pid = uval & FUTEX_TID_MASK;
    - u32 uval2;
    - int ret;
    -
    - /*
    - * Userspace might have messed up non-PI and PI futexes [3]
    - */
    - if (unlikely(!pi_state))
    - return -EINVAL;
    -
    - /*
    - * We get here with hb->lock held, and having found a
    - * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
    - * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
    - * which in turn means that futex_lock_pi() still has a reference on
    - * our pi_state.
    - *
    - * The waiter holding a reference on @pi_state also protects against
    - * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
    - * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
    - * free pi_state before we can take a reference ourselves.
    - */
    - WARN_ON(!refcount_read(&pi_state->refcount));
    -
    - /*
    - * Now that we have a pi_state, we can acquire wait_lock
    - * and do the state validation.
    - */
    - raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    -
    - /*
    - * Since {uval, pi_state} is serialized by wait_lock, and our current
    - * uval was read without holding it, it can have changed. Verify it
    - * still is what we expect it to be, otherwise retry the entire
    - * operation.
    - */
    - if (get_futex_value_locked(&uval2, uaddr))
    - goto out_efault;
    -
    - if (uval != uval2)
    - goto out_eagain;
    -
    - /*
    - * Handle the owner died case:
    - */
    - if (uval & FUTEX_OWNER_DIED) {
    - /*
    - * exit_pi_state_list sets owner to NULL and wakes the
    - * topmost waiter. The task which acquires the
    - * pi_state->rt_mutex will fixup owner.
    - */
    - if (!pi_state->owner) {
    - /*
    - * No pi state owner, but the user space TID
    - * is not 0. Inconsistent state. [5]
    - */
    - if (pid)
    - goto out_einval;
    - /*
    - * Take a ref on the state and return success. [4]
    - */
    - goto out_attach;
    - }
    -
    - /*
    - * If TID is 0, then either the dying owner has not
    - * yet executed exit_pi_state_list() or some waiter
    - * acquired the rtmutex in the pi state, but did not
    - * yet fixup the TID in user space.
    - *
    - * Take a ref on the state and return success. [6]
    - */
    - if (!pid)
    - goto out_attach;
    - } else {
    - /*
    - * If the owner died bit is not set, then the pi_state
    - * must have an owner. [7]
    - */
    - if (!pi_state->owner)
    - goto out_einval;
    - }
    -
    - /*
    - * Bail out if user space manipulated the futex value. If pi
    - * state exists then the owner TID must be the same as the
    - * user space TID. [9/10]
    - */
    - if (pid != task_pid_vnr(pi_state->owner))
    - goto out_einval;
    -
    -out_attach:
    - get_pi_state(pi_state);
    - raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    - *ps = pi_state;
    - return 0;
    -
    -out_einval:
    - ret = -EINVAL;
    - goto out_error;
    -
    -out_eagain:
    - ret = -EAGAIN;
    - goto out_error;
    -
    -out_efault:
    - ret = -EFAULT;
    - goto out_error;
    -
    -out_error:
    - raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    - return ret;
    -}
    -
    -/**
    - * wait_for_owner_exiting - Block until the owner has exited
    - * @ret: owner's current futex lock status
    - * @exiting: Pointer to the exiting task
    - *
    - * Caller must hold a refcount on @exiting.
    - */
    -static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
    -{
    - if (ret != -EBUSY) {
    - WARN_ON_ONCE(exiting);
    - return;
    - }
    -
    - if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
    - return;
    -
    - mutex_lock(&exiting->futex_exit_mutex);
    - /*
    - * No point in doing state checking here. If the waiter got here
    - * while the task was in exec()->exec_futex_release() then it can
    - * have any FUTEX_STATE_* value when the waiter has acquired the
    - * mutex. OK, if running, EXITING or DEAD if it reached exit()
    - * already. Highly unlikely and not a problem. Just one more round
    - * through the futex maze.
    - */
    - mutex_unlock(&exiting->futex_exit_mutex);
    -
    - put_task_struct(exiting);
    -}
    -
    -static int handle_exit_race(u32 __user *uaddr, u32 uval,
    - struct task_struct *tsk)
    -{
    - u32 uval2;
    -
    - /*
    - * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
    - * caller that the alleged owner is busy.
    - */
    - if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
    - return -EBUSY;
    -
    - /*
    - * Reread the user space value to handle the following situation:
    - *
    - * CPU0 CPU1
    - *
    - * sys_exit() sys_futex()
    - * do_exit() futex_lock_pi()
    - * futex_lock_pi_atomic()
    - * exit_signals(tsk) No waiters:
    - * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
    - * mm_release(tsk) Set waiter bit
    - * exit_robust_list(tsk) { *uaddr = 0x80000PID;
    - * Set owner died attach_to_pi_owner() {
    - * *uaddr = 0xC0000000; tsk = get_task(PID);
    - * } if (!tsk->flags & PF_EXITING) {
    - * ... attach();
    - * tsk->futex_state = } else {
    - * FUTEX_STATE_DEAD; if (tsk->futex_state !=
    - * FUTEX_STATE_DEAD)
    - * return -EAGAIN;
    - * return -ESRCH; <--- FAIL
    - * }
    - *
    - * Returning ESRCH unconditionally is wrong here because the
    - * user space value has been changed by the exiting task.
    - *
    - * The same logic applies to the case where the exiting task is
    - * already gone.
    - */
    - if (get_futex_value_locked(&uval2, uaddr))
    - return -EFAULT;
    -
    - /* If the user space value has changed, try again. */
    - if (uval2 != uval)
    - return -EAGAIN;
    -
    - /*
    - * The exiting task did not have a robust list, the robust list was
    - * corrupted or the user space value in *uaddr is simply bogus.
    - * Give up and tell user space.
    - */
    - return -ESRCH;
    -}
    -
    -static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
    - struct futex_pi_state **ps)
    -{
    - /*
    - * No existing pi state. First waiter. [2]
    - *
    - * This creates pi_state, we have hb->lock held, this means nothing can
    - * observe this state, wait_lock is irrelevant.
    - */
    - struct futex_pi_state *pi_state = alloc_pi_state();
    -
    - /*
    - * Initialize the pi_mutex in locked state and make @p
    - * the owner of it:
    - */
    - rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
    -
    - /* Store the key for possible exit cleanups: */
    - pi_state->key = *key;
    -
    - WARN_ON(!list_empty(&pi_state->list));
    - list_add(&pi_state->list, &p->pi_state_list);
    - /*
    - * Assignment without holding pi_state->pi_mutex.wait_lock is safe
    - * because there is no concurrency as the object is not published yet.
    - */
    - pi_state->owner = p;
    -
    - *ps = pi_state;
    -}
    -/*
    - * Lookup the task for the TID provided from user space and attach to
    - * it after doing proper sanity checks.
    - */
    -static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
    - struct futex_pi_state **ps,
    - struct task_struct **exiting)
    -{
    - pid_t pid = uval & FUTEX_TID_MASK;
    - struct task_struct *p;
    -
    - /*
    - * We are the first waiter - try to look up the real owner and attach
    - * the new pi_state to it, but bail out when TID = 0 [1]
    - *
    - * The !pid check is paranoid. None of the call sites should end up
    - * with pid == 0, but better safe than sorry. Let the caller retry
    - */
    - if (!pid)
    - return -EAGAIN;
    - p = find_get_task_by_vpid(pid);
    - if (!p)
    - return handle_exit_race(uaddr, uval, NULL);
    -
    - if (unlikely(p->flags & PF_KTHREAD)) {
    - put_task_struct(p);
    - return -EPERM;
    - }
    -
    - /*
    - * We need to look at the task state to figure out, whether the
    - * task is exiting. To protect against the change of the task state
    - * in futex_exit_release(), we do this protected by p->pi_lock:
    - */
    - raw_spin_lock_irq(&p->pi_lock);
    - if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
    - /*
    - * The task is on the way out. When the futex state is
    - * FUTEX_STATE_DEAD, we know that the task has finished
    - * the cleanup:
    - */
    - int ret = handle_exit_race(uaddr, uval, p);
    -
    - raw_spin_unlock_irq(&p->pi_lock);
    - /*
    - * If the owner task is between FUTEX_STATE_EXITING and
    - * FUTEX_STATE_DEAD then store the task pointer and keep
    - * the reference on the task struct. The calling code will
    - * drop all locks, wait for the task to reach
    - * FUTEX_STATE_DEAD and then drop the refcount. This is
    - * required to prevent a live lock when the current task
    - * preempted the exiting task between the two states.
    - */
    - if (ret == -EBUSY)
    - *exiting = p;
    - else
    - put_task_struct(p);
    - return ret;
    - }
    -
    - __attach_to_pi_owner(p, key, ps);
    - raw_spin_unlock_irq(&p->pi_lock);
    -
    - put_task_struct(p);
    -
    - return 0;
    -}
    -
    -static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
    -{
    - int err;
    - u32 curval;
    -
    - if (unlikely(should_fail_futex(true)))
    - return -EFAULT;
    -
    - err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
    - if (unlikely(err))
    - return err;
    -
    - /* If user space value changed, let the caller retry */
    - return curval != uval ? -EAGAIN : 0;
    -}
    -
    -/**
    - * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
    - * @uaddr: the pi futex user address
    - * @hb: the pi futex hash bucket
    - * @key: the futex key associated with uaddr and hb
    - * @ps: the pi_state pointer where we store the result of the
    - * lookup
    - * @task: the task to perform the atomic lock work for. This will
    - * be "current" except in the case of requeue pi.
    - * @exiting: Pointer to store the task pointer of the owner task
    - * which is in the middle of exiting
    - * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
    - *
    - * Return:
    - * - 0 - ready to wait;
    - * - 1 - acquired the lock;
    - * - <0 - error
    - *
    - * The hb->lock must be held by the caller.
    - *
    - * @exiting is only set when the return value is -EBUSY. If so, this holds
    - * a refcount on the exiting task on return and the caller needs to drop it
    - * after waiting for the exit to complete.
    - */
    -static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
    - union futex_key *key,
    - struct futex_pi_state **ps,
    - struct task_struct *task,
    - struct task_struct **exiting,
    - int set_waiters)
    -{
    - u32 uval, newval, vpid = task_pid_vnr(task);
    - struct futex_q *top_waiter;
    - int ret;
    -
    - /*
    - * Read the user space value first so we can validate a few
    - * things before proceeding further.
    - */
    - if (get_futex_value_locked(&uval, uaddr))
    - return -EFAULT;
    -
    - if (unlikely(should_fail_futex(true)))
    - return -EFAULT;
    -
    - /*
    - * Detect deadlocks.
    - */
    - if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
    - return -EDEADLK;
    -
    - if ((unlikely(should_fail_futex(true))))
    - return -EDEADLK;
    -
    - /*
    - * Lookup existing state first. If it exists, try to attach to
    - * its pi_state.
    - */
    - top_waiter = futex_top_waiter(hb, key);
    - if (top_waiter)
    - return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
    -
    - /*
    - * No waiter and user TID is 0. We are here because the
    - * waiters or the owner died bit is set or called from
    - * requeue_cmp_pi or for whatever reason something took the
    - * syscall.
    - */
    - if (!(uval & FUTEX_TID_MASK)) {
    - /*
    - * We take over the futex. No other waiters and the user space
    - * TID is 0. We preserve the owner died bit.
    - */
    - newval = uval & FUTEX_OWNER_DIED;
    - newval |= vpid;
    -
    - /* The futex requeue_pi code can enforce the waiters bit */
    - if (set_waiters)
    - newval |= FUTEX_WAITERS;
    -
    - ret = lock_pi_update_atomic(uaddr, uval, newval);
    - if (ret)
    - return ret;
    -
    - /*
    - * If the waiter bit was requested the caller also needs PI
    - * state attached to the new owner of the user space futex.
    - *
    - * @task is guaranteed to be alive and it cannot be exiting
    - * because it is either sleeping or waiting in
    - * futex_requeue_pi_wakeup_sync().
    - *
    - * No need to do the full attach_to_pi_owner() exercise
    - * because @task is known and valid.
    - */
    - if (set_waiters) {
    - raw_spin_lock_irq(&task->pi_lock);
    - __attach_to_pi_owner(task, key, ps);
    - raw_spin_unlock_irq(&task->pi_lock);
    - }
    - return 1;
    - }
    -
    - /*
    - * First waiter. Set the waiters bit before attaching ourself to
    - * the owner. If owner tries to unlock, it will be forced into
    - * the kernel and blocked on hb->lock.
    - */
    - newval = uval | FUTEX_WAITERS;
    - ret = lock_pi_update_atomic(uaddr, uval, newval);
    - if (ret)
    - return ret;
    - /*
    - * If the update of the user space value succeeded, we try to
    - * attach to the owner. If that fails, no harm done, we only
    - * set the FUTEX_WAITERS bit in the user space variable.
    - */
    - return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
    -}
    -
    -/**
    - * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
    - * @q: The futex_q to unqueue
    - *
    - * The q->lock_ptr must not be NULL and must be held by the caller.
    - */
    -static void __unqueue_futex(struct futex_q *q)
    -{
    - struct futex_hash_bucket *hb;
    -
    - if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
    - return;
    - lockdep_assert_held(q->lock_ptr);
    -
    - hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
    - plist_del(&q->list, &hb->chain);
    - hb_waiters_dec(hb);
    -}
    -
    -/*
    - * The hash bucket lock must be held when this is called.
    - * Afterwards, the futex_q must not be accessed. Callers
    - * must ensure to later call wake_up_q() for the actual
    - * wakeups to occur.
    - */
    -static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
    -{
    - struct task_struct *p = q->task;
    -
    - if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
    - return;
    -
    - get_task_struct(p);
    - __unqueue_futex(q);
    - /*
    - * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
    - * is written, without taking any locks. This is possible in the event
    - * of a spurious wakeup, for example. A memory barrier is required here
    - * to prevent the following store to lock_ptr from getting ahead of the
    - * plist_del in __unqueue_futex().
    - */
    - smp_store_release(&q->lock_ptr, NULL);
    -
    - /*
    - * Queue the task for later wakeup for after we've released
    - * the hb->lock.
    - */
    - wake_q_add_safe(wake_q, p);
    -}
    -
    -/*
    - * Caller must hold a reference on @pi_state.
    - */
    -static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
    -{
    - struct rt_mutex_waiter *top_waiter;
    - struct task_struct *new_owner;
    - bool postunlock = false;
    - DEFINE_RT_WAKE_Q(wqh);
    - u32 curval, newval;
    - int ret = 0;
    -
    - top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
    - if (WARN_ON_ONCE(!top_waiter)) {
    - /*
    - * As per the comment in futex_unlock_pi() this should not happen.
    - *
    - * When this happens, give up our locks and try again, giving
    - * the futex_lock_pi() instance time to complete, either by
    - * waiting on the rtmutex or removing itself from the futex
    - * queue.
    - */
    - ret = -EAGAIN;
    - goto out_unlock;
    - }
    -
    - new_owner = top_waiter->task;
    -
    - /*
    - * We pass it to the next owner. The WAITERS bit is always kept
    - * enabled while there is PI state around. We cleanup the owner
    - * died bit, because we are the owner.
    - */
    - newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
    -
    - if (unlikely(should_fail_futex(true))) {
    - ret = -EFAULT;
    - goto out_unlock;
    - }
    -
    - ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
    - if (!ret && (curval != uval)) {
    - /*
    - * If a unconditional UNLOCK_PI operation (user space did not
    - * try the TID->0 transition) raced with a waiter setting the
    - * FUTEX_WAITERS flag between get_user() and locking the hash
    - * bucket lock, retry the operation.
    - */
    - if ((FUTEX_TID_MASK & curval) == uval)
    - ret = -EAGAIN;
    - else
    - ret = -EINVAL;
    - }
    -
    - if (!ret) {
    - /*
    - * This is a point of no return; once we modified the uval
    - * there is no going back and subsequent operations must
    - * not fail.
    - */
    - pi_state_update_owner(pi_state, new_owner);
    - postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
    - }
    -
    -out_unlock:
    - raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    -
    - if (postunlock)
    - rt_mutex_postunlock(&wqh);
    -
    - return ret;
    -}
    -
    -/*
    - * Express the locking dependencies for lockdep:
    - */
    -static inline void
    -double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
    -{
    - if (hb1 <= hb2) {
    - spin_lock(&hb1->lock);
    - if (hb1 < hb2)
    - spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
    - } else { /* hb1 > hb2 */
    - spin_lock(&hb2->lock);
    - spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
    - }
    -}
    -
    -static inline void
    -double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
    -{
    - spin_unlock(&hb1->lock);
    - if (hb1 != hb2)
    - spin_unlock(&hb2->lock);
    -}
    -
    -/*
    - * Wake up waiters matching bitset queued on this futex (uaddr).
    - */
    -static int
    -futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
    -{
    - struct futex_hash_bucket *hb;
    - struct futex_q *this, *next;
    - union futex_key key = FUTEX_KEY_INIT;
    - int ret;
    - DEFINE_WAKE_Q(wake_q);
    -
    - if (!bitset)
    - return -EINVAL;
    -
    - ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
    - if (unlikely(ret != 0))
    - return ret;
    -
    - hb = hash_futex(&key);
    -
    - /* Make sure we really have tasks to wakeup */
    - if (!hb_waiters_pending(hb))
    - return ret;
    -
    - spin_lock(&hb->lock);
    -
    - plist_for_each_entry_safe(this, next, &hb->chain, list) {
    - if (match_futex (&this->key, &key)) {
    - if (this->pi_state || this->rt_waiter) {
    - ret = -EINVAL;
    - break;
    - }
    -
    - /* Check if one of the bits is set in both bitsets */
    - if (!(this->bitset & bitset))
    - continue;
    -
    - mark_wake_futex(&wake_q, this);
    - if (++ret >= nr_wake)
    - break;
    - }
    - }
    -
    - spin_unlock(&hb->lock);
    - wake_up_q(&wake_q);
    - return ret;
    -}
    -
    -static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
    -{
    - unsigned int op = (encoded_op & 0x70000000) >> 28;
    - unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
    - int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
    - int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
    - int oldval, ret;
    -
    - if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
    - if (oparg < 0 || oparg > 31) {
    - char comm[sizeof(current->comm)];
    - /*
    - * kill this print and return -EINVAL when userspace
    - * is sane again
    - */
    - pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
    - get_task_comm(comm, current), oparg);
    - oparg &= 31;
    - }
    - oparg = 1 << oparg;
    - }
    -
    - pagefault_disable();
    - ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
    - pagefault_enable();
    - if (ret)
    - return ret;
    -
    - switch (cmp) {
    - case FUTEX_OP_CMP_EQ:
    - return oldval == cmparg;
    - case FUTEX_OP_CMP_NE:
    - return oldval != cmparg;
    - case FUTEX_OP_CMP_LT:
    - return oldval < cmparg;
    - case FUTEX_OP_CMP_GE:
    - return oldval >= cmparg;
    - case FUTEX_OP_CMP_LE:
    - return oldval <= cmparg;
    - case FUTEX_OP_CMP_GT:
    - return oldval > cmparg;
    - default:
    - return -ENOSYS;
    - }
    -}
    -
    -/*
    - * Wake up all waiters hashed on the physical page that is mapped
    - * to this virtual address:
    - */
    -static int
    -futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
    - int nr_wake, int nr_wake2, int op)
    -{
    - union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
    - struct futex_hash_bucket *hb1, *hb2;
    - struct futex_q *this, *next;
    - int ret, op_ret;
    - DEFINE_WAKE_Q(wake_q);
    -
    -retry:
    - ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
    - if (unlikely(ret != 0))
    - return ret;
    - ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
    - if (unlikely(ret != 0))
    - return ret;
    -
    - hb1 = hash_futex(&key1);
    - hb2 = hash_futex(&key2);
    -
    -retry_private:
    - double_lock_hb(hb1, hb2);
    - op_ret = futex_atomic_op_inuser(op, uaddr2);
    - if (unlikely(op_ret < 0)) {
    - double_unlock_hb(hb1, hb2);
    -
    - if (!IS_ENABLED(CONFIG_MMU) ||
    - unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
    - /*
    - * we don't get EFAULT from MMU faults if we don't have
    - * an MMU, but we might get them from range checking
    - */
    - ret = op_ret;
    - return ret;
    - }
    -
    - if (op_ret == -EFAULT) {
    - ret = fault_in_user_writeable(uaddr2);
    - if (ret)
    - return ret;
    - }
    -
    - cond_resched();
    - if (!(flags & FLAGS_SHARED))
    - goto retry_private;
    - goto retry;
    - }
    -
    - plist_for_each_entry_safe(this, next, &hb1->chain, list) {
    - if (match_futex (&this->key, &key1)) {
    - if (this->pi_state || this->rt_waiter) {
    - ret = -EINVAL;
    - goto out_unlock;
    - }
    - mark_wake_futex(&wake_q, this);
    - if (++ret >= nr_wake)
    - break;
    - }
    - }
    -
    - if (op_ret > 0) {
    - op_ret = 0;
    - plist_for_each_entry_safe(this, next, &hb2->chain, list) {
    - if (match_futex (&this->key, &key2)) {
    - if (this->pi_state || this->rt_waiter) {
    - ret = -EINVAL;
    - goto out_unlock;
    - }
    - mark_wake_futex(&wake_q, this);
    - if (++op_ret >= nr_wake2)
    - break;
    - }
    - }
    - ret += op_ret;
    - }
    -
    -out_unlock:
    - double_unlock_hb(hb1, hb2);
    - wake_up_q(&wake_q);
    - return ret;
    -}
    -
    -/**
    - * requeue_futex() - Requeue a futex_q from one hb to another
    - * @q: the futex_q to requeue
    - * @hb1: the source hash_bucket
    - * @hb2: the target hash_bucket
    - * @key2: the new key for the requeued futex_q
    - */
    -static inline
    -void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
    - struct futex_hash_bucket *hb2, union futex_key *key2)
    -{
    -
    - /*
    - * If key1 and key2 hash to the same bucket, no need to
    - * requeue.
    - */
    - if (likely(&hb1->chain != &hb2->chain)) {
    - plist_del(&q->list, &hb1->chain);
    - hb_waiters_dec(hb1);
    - hb_waiters_inc(hb2);
    - plist_add(&q->list, &hb2->chain);
    - q->lock_ptr = &hb2->lock;
    - }
    - q->key = *key2;
    -}
    -
    -static inline bool futex_requeue_pi_prepare(struct futex_q *q,
    - struct futex_pi_state *pi_state)
    -{
    - int old, new;
    -
    - /*
    - * Set state to Q_REQUEUE_PI_IN_PROGRESS unless an early wakeup has
    - * already set Q_REQUEUE_PI_IGNORE to signal that requeue should
    - * ignore the waiter.
    - */
    - old = atomic_read_acquire(&q->requeue_state);
    - do {
    - if (old == Q_REQUEUE_PI_IGNORE)
    - return false;
    -
    - /*
    - * futex_proxy_trylock_atomic() might have set it to
    - * IN_PROGRESS and a interleaved early wake to WAIT.
    - *
    - * It was considered to have an extra state for that
    - * trylock, but that would just add more conditionals
    - * all over the place for a dubious value.
    - */
    - if (old != Q_REQUEUE_PI_NONE)
    - break;
    -
    - new = Q_REQUEUE_PI_IN_PROGRESS;
    - } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
    -
    - q->pi_state = pi_state;
    - return true;
    -}
    -
    -static inline void futex_requeue_pi_complete(struct futex_q *q, int locked)
    -{
    - int old, new;
    -
    - old = atomic_read_acquire(&q->requeue_state);
    - do {
    - if (old == Q_REQUEUE_PI_IGNORE)
    - return;
    -
    - if (locked >= 0) {
    - /* Requeue succeeded. Set DONE or LOCKED */
    - WARN_ON_ONCE(old != Q_REQUEUE_PI_IN_PROGRESS &&
    - old != Q_REQUEUE_PI_WAIT);
    - new = Q_REQUEUE_PI_DONE + locked;
    - } else if (old == Q_REQUEUE_PI_IN_PROGRESS) {
    - /* Deadlock, no early wakeup interleave */
    - new = Q_REQUEUE_PI_NONE;
    - } else {
    - /* Deadlock, early wakeup interleave. */
    - WARN_ON_ONCE(old != Q_REQUEUE_PI_WAIT);
    - new = Q_REQUEUE_PI_IGNORE;
    - }
    - } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
    -
    -#ifdef CONFIG_PREEMPT_RT
    - /* If the waiter interleaved with the requeue let it know */
    - if (unlikely(old == Q_REQUEUE_PI_WAIT))
    - rcuwait_wake_up(&q->requeue_wait);
    -#endif
    -}
    -
    -static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q)
    -{
    - int old, new;
    -
    - old = atomic_read_acquire(&q->requeue_state);
    - do {
    - /* Is requeue done already? */
    - if (old >= Q_REQUEUE_PI_DONE)
    - return old;
    -
    - /*
    - * If not done, then tell the requeue code to either ignore
    - * the waiter or to wake it up once the requeue is done.
    - */
    - new = Q_REQUEUE_PI_WAIT;
    - if (old == Q_REQUEUE_PI_NONE)
    - new = Q_REQUEUE_PI_IGNORE;
    - } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
    -
    - /* If the requeue was in progress, wait for it to complete */
    - if (old == Q_REQUEUE_PI_IN_PROGRESS) {
    -#ifdef CONFIG_PREEMPT_RT
    - rcuwait_wait_event(&q->requeue_wait,
    - atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT,
    - TASK_UNINTERRUPTIBLE);
    -#else
    - (void)atomic_cond_read_relaxed(&q->requeue_state, VAL != Q_REQUEUE_PI_WAIT);
    -#endif
    - }
    -
    - /*
    - * Requeue is now either prohibited or complete. Reread state
    - * because during the wait above it might have changed. Nothing
    - * will modify q->requeue_state after this point.
    - */
    - return atomic_read(&q->requeue_state);
    -}
    -
    -/**
    - * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
    - * @q: the futex_q
    - * @key: the key of the requeue target futex
    - * @hb: the hash_bucket of the requeue target futex
    - *
    - * During futex_requeue, with requeue_pi=1, it is possible to acquire the
    - * target futex if it is uncontended or via a lock steal.
    - *
    - * 1) Set @q::key to the requeue target futex key so the waiter can detect
    - * the wakeup on the right futex.
    - *
    - * 2) Dequeue @q from the hash bucket.
    - *
    - * 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock
    - * acquisition.
    - *
    - * 4) Set the q->lock_ptr to the requeue target hb->lock for the case that
    - * the waiter has to fixup the pi state.
    - *
    - * 5) Complete the requeue state so the waiter can make progress. After
    - * this point the waiter task can return from the syscall immediately in
    - * case that the pi state does not have to be fixed up.
    - *
    - * 6) Wake the waiter task.
    - *
    - * Must be called with both q->lock_ptr and hb->lock held.
    - */
    -static inline
    -void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
    - struct futex_hash_bucket *hb)
    -{
    - q->key = *key;
    -
    - __unqueue_futex(q);
    -
    - WARN_ON(!q->rt_waiter);
    - q->rt_waiter = NULL;
    -
    - q->lock_ptr = &hb->lock;
    -
    - /* Signal locked state to the waiter */
    - futex_requeue_pi_complete(q, 1);
    - wake_up_state(q->task, TASK_NORMAL);
    -}
    -
    -/**
    - * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
    - * @pifutex: the user address of the to futex
    - * @hb1: the from futex hash bucket, must be locked by the caller
    - * @hb2: the to futex hash bucket, must be locked by the caller
    - * @key1: the from futex key
    - * @key2: the to futex key
    - * @ps: address to store the pi_state pointer
    - * @exiting: Pointer to store the task pointer of the owner task
    - * which is in the middle of exiting
    - * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
    - *
    - * Try and get the lock on behalf of the top waiter if we can do it atomically.
    - * Wake the top waiter if we succeed. If the caller specified set_waiters,
    - * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
    - * hb1 and hb2 must be held by the caller.
    - *
    - * @exiting is only set when the return value is -EBUSY. If so, this holds
    - * a refcount on the exiting task on return and the caller needs to drop it
    - * after waiting for the exit to complete.
    - *
    - * Return:
    - * - 0 - failed to acquire the lock atomically;
    - * - >0 - acquired the lock, return value is vpid of the top_waiter
    - * - <0 - error
    - */
    -static int
    -futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
    - struct futex_hash_bucket *hb2, union futex_key *key1,
    - union futex_key *key2, struct futex_pi_state **ps,
    - struct task_struct **exiting, int set_waiters)
    -{
    - struct futex_q *top_waiter = NULL;
    - u32 curval;
    - int ret;
    -
    - if (get_futex_value_locked(&curval, pifutex))
    - return -EFAULT;
    -
    - if (unlikely(should_fail_futex(true)))
    - return -EFAULT;
    -
    - /*
    - * Find the top_waiter and determine if there are additional waiters.
    - * If the caller intends to requeue more than 1 waiter to pifutex,
    - * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
    - * as we have means to handle the possible fault. If not, don't set
    - * the bit unnecessarily as it will force the subsequent unlock to enter
    - * the kernel.
    - */
    - top_waiter = futex_top_waiter(hb1, key1);
    -
    - /* There are no waiters, nothing for us to do. */
    - if (!top_waiter)
    - return 0;
    -
    - /*
    - * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
    - * and waiting on the 'waitqueue' futex which is always !PI.
    - */
    - if (!top_waiter->rt_waiter || top_waiter->pi_state)
    - return -EINVAL;
    -
    - /* Ensure we requeue to the expected futex. */
    - if (!match_futex(top_waiter->requeue_pi_key, key2))
    - return -EINVAL;
    -
    - /* Ensure that this does not race against an early wakeup */
    - if (!futex_requeue_pi_prepare(top_waiter, NULL))
    - return -EAGAIN;
    -
    - /*
    - * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
    - * in the contended case or if @set_waiters is true.
    - *
    - * In the contended case PI state is attached to the lock owner. If
    - * the user space lock can be acquired then PI state is attached to
    - * the new owner (@top_waiter->task) when @set_waiters is true.
    - */
    - ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
    - exiting, set_waiters);
    - if (ret == 1) {
    - /*
    - * Lock was acquired in user space and PI state was
    - * attached to @top_waiter->task. That means state is fully
    - * consistent and the waiter can return to user space
    - * immediately after the wakeup.
    - */
    - requeue_pi_wake_futex(top_waiter, key2, hb2);
    - } else if (ret < 0) {
    - /* Rewind top_waiter::requeue_state */
    - futex_requeue_pi_complete(top_waiter, ret);
    - } else {
    - /*
    - * futex_lock_pi_atomic() did not acquire the user space
    - * futex, but managed to establish the proxy lock and pi
    - * state. top_waiter::requeue_state cannot be fixed up here
    - * because the waiter is not enqueued on the rtmutex
    - * yet. This is handled at the callsite depending on the
    - * result of rt_mutex_start_proxy_lock() which is
    - * guaranteed to be reached with this function returning 0.
    - */
    - }
    - return ret;
    -}
    -
    -/**
    - * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
    - * @uaddr1: source futex user address
    - * @flags: futex flags (FLAGS_SHARED, etc.)
    - * @uaddr2: target futex user address
    - * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
    - * @nr_requeue: number of waiters to requeue (0-INT_MAX)
    - * @cmpval: @uaddr1 expected value (or %NULL)
    - * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
    - * pi futex (pi to pi requeue is not supported)
    - *
    - * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
    - * uaddr2 atomically on behalf of the top waiter.
    - *
    - * Return:
    - * - >=0 - on success, the number of tasks requeued or woken;
    - * - <0 - on error
    - */
    -static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
    - u32 __user *uaddr2, int nr_wake, int nr_requeue,
    - u32 *cmpval, int requeue_pi)
    -{
    - union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
    - int task_count = 0, ret;
    - struct futex_pi_state *pi_state = NULL;
    - struct futex_hash_bucket *hb1, *hb2;
    - struct futex_q *this, *next;
    - DEFINE_WAKE_Q(wake_q);
    -
    - if (nr_wake < 0 || nr_requeue < 0)
    - return -EINVAL;
    -
    - /*
    - * When PI not supported: return -ENOSYS if requeue_pi is true,
    - * consequently the compiler knows requeue_pi is always false past
    - * this point which will optimize away all the conditional code
    - * further down.
    - */
    - if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
    - return -ENOSYS;
    -
    - if (requeue_pi) {
    - /*
    - * Requeue PI only works on two distinct uaddrs. This
    - * check is only valid for private futexes. See below.
    - */
    - if (uaddr1 == uaddr2)
    - return -EINVAL;
    -
    - /*
    - * futex_requeue() allows the caller to define the number
    - * of waiters to wake up via the @nr_wake argument. With
    - * REQUEUE_PI, waking up more than one waiter is creating
    - * more problems than it solves. Waking up a waiter makes
    - * only sense if the PI futex @uaddr2 is uncontended as
    - * this allows the requeue code to acquire the futex
    - * @uaddr2 before waking the waiter. The waiter can then
    - * return to user space without further action. A secondary
    - * wakeup would just make the futex_wait_requeue_pi()
    - * handling more complex, because that code would have to
    - * look up pi_state and do more or less all the handling
    - * which the requeue code has to do for the to be requeued
    - * waiters. So restrict the number of waiters to wake to
    - * one, and only wake it up when the PI futex is
    - * uncontended. Otherwise requeue it and let the unlock of
    - * the PI futex handle the wakeup.
    - *
    - * All REQUEUE_PI users, e.g. pthread_cond_signal() and
    - * pthread_cond_broadcast() must use nr_wake=1.
    - */
    - if (nr_wake != 1)
    - return -EINVAL;
    -
    - /*
    - * requeue_pi requires a pi_state, try to allocate it now
    - * without any locks in case it fails.
    - */
    - if (refill_pi_state_cache())
    - return -ENOMEM;
    - }
    -
    -retry:
    - ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
    - if (unlikely(ret != 0))
    - return ret;
    - ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
    - requeue_pi ? FUTEX_WRITE : FUTEX_READ);
    - if (unlikely(ret != 0))
    - return ret;
    -
    - /*
    - * The check above which compares uaddrs is not sufficient for
    - * shared futexes. We need to compare the keys:
    - */
    - if (requeue_pi && match_futex(&key1, &key2))
    - return -EINVAL;
    -
    - hb1 = hash_futex(&key1);
    - hb2 = hash_futex(&key2);
    -
    -retry_private:
    - hb_waiters_inc(hb2);
    - double_lock_hb(hb1, hb2);
    -
    - if (likely(cmpval != NULL)) {
    - u32 curval;
    -
    - ret = get_futex_value_locked(&curval, uaddr1);
    -
    - if (unlikely(ret)) {
    - double_unlock_hb(hb1, hb2);
    - hb_waiters_dec(hb2);
    -
    - ret = get_user(curval, uaddr1);
    - if (ret)
    - return ret;
    -
    - if (!(flags & FLAGS_SHARED))
    - goto retry_private;
    -
    - goto retry;
    - }
    - if (curval != *cmpval) {
    - ret = -EAGAIN;
    - goto out_unlock;
    - }
    - }
    -
    - if (requeue_pi) {
    - struct task_struct *exiting = NULL;
    -
    - /*
    - * Attempt to acquire uaddr2 and wake the top waiter. If we
    - * intend to requeue waiters, force setting the FUTEX_WAITERS
    - * bit. We force this here where we are able to easily handle
    - * faults rather in the requeue loop below.
    - *
    - * Updates topwaiter::requeue_state if a top waiter exists.
    - */
    - ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
    - &key2, &pi_state,
    - &exiting, nr_requeue);
    -
    - /*
    - * At this point the top_waiter has either taken uaddr2 or
    - * is waiting on it. In both cases pi_state has been
    - * established and an initial refcount on it. In case of an
    - * error there's nothing.
    - *
    - * The top waiter's requeue_state is up to date:
    - *
    - * - If the lock was acquired atomically (ret == 1), then
    - * the state is Q_REQUEUE_PI_LOCKED.
    - *
    - * The top waiter has been dequeued and woken up and can
    - * return to user space immediately. The kernel/user
    - * space state is consistent. In case that there must be
    - * more waiters requeued the WAITERS bit in the user
    - * space futex is set so the top waiter task has to go
    - * into the syscall slowpath to unlock the futex. This
    - * will block until this requeue operation has been
    - * completed and the hash bucket locks have been
    - * dropped.
    - *
    - * - If the trylock failed with an error (ret < 0) then
    - * the state is either Q_REQUEUE_PI_NONE, i.e. "nothing
    - * happened", or Q_REQUEUE_PI_IGNORE when there was an
    - * interleaved early wakeup.
    - *
    - * - If the trylock did not succeed (ret == 0) then the
    - * state is either Q_REQUEUE_PI_IN_PROGRESS or
    - * Q_REQUEUE_PI_WAIT if an early wakeup interleaved.
    - * This will be cleaned up in the loop below, which
    - * cannot fail because futex_proxy_trylock_atomic() did
    - * the same sanity checks for requeue_pi as the loop
    - * below does.
    - */
    - switch (ret) {
    - case 0:
    - /* We hold a reference on the pi state. */
    - break;
    -
    - case 1:
    - /*
    - * futex_proxy_trylock_atomic() acquired the user space
    - * futex. Adjust task_count.
    - */
    - task_count++;
    - ret = 0;
    - break;
    -
    - /*
    - * If the above failed, then pi_state is NULL and
    - * waiter::requeue_state is correct.
    - */
    - case -EFAULT:
    - double_unlock_hb(hb1, hb2);
    - hb_waiters_dec(hb2);
    - ret = fault_in_user_writeable(uaddr2);
    - if (!ret)
    - goto retry;
    - return ret;
    - case -EBUSY:
    - case -EAGAIN:
    - /*
    - * Two reasons for this:
    - * - EBUSY: Owner is exiting and we just wait for the
    - * exit to complete.
    - * - EAGAIN: The user space value changed.
    - */
    - double_unlock_hb(hb1, hb2);
    - hb_waiters_dec(hb2);
    - /*
    - * Handle the case where the owner is in the middle of
    - * exiting. Wait for the exit to complete otherwise
    - * this task might loop forever, aka. live lock.
    - */
    - wait_for_owner_exiting(ret, exiting);
    - cond_resched();
    - goto retry;
    - default:
    - goto out_unlock;
    - }
    - }
    -
    - plist_for_each_entry_safe(this, next, &hb1->chain, list) {
    - if (task_count - nr_wake >= nr_requeue)
    - break;
    -
    - if (!match_futex(&this->key, &key1))
    - continue;
    -
    - /*
    - * FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI should always
    - * be paired with each other and no other futex ops.
    - *
    - * We should never be requeueing a futex_q with a pi_state,
    - * which is awaiting a futex_unlock_pi().
    - */
    - if ((requeue_pi && !this->rt_waiter) ||
    - (!requeue_pi && this->rt_waiter) ||
    - this->pi_state) {
    - ret = -EINVAL;
    - break;
    - }
    -
    - /* Plain futexes just wake or requeue and are done */
    - if (!requeue_pi) {
    - if (++task_count <= nr_wake)
    - mark_wake_futex(&wake_q, this);
    - else
    - requeue_futex(this, hb1, hb2, &key2);
    - continue;
    - }
    -
    - /* Ensure we requeue to the expected futex for requeue_pi. */
    - if (!match_futex(this->requeue_pi_key, &key2)) {
    - ret = -EINVAL;
    - break;
    - }
    -
    - /*
    - * Requeue nr_requeue waiters and possibly one more in the case
    - * of requeue_pi if we couldn't acquire the lock atomically.
    - *
    - * Prepare the waiter to take the rt_mutex. Take a refcount
    - * on the pi_state and store the pointer in the futex_q
    - * object of the waiter.
    - */
    - get_pi_state(pi_state);
    -
    - /* Don't requeue when the waiter is already on the way out. */
    - if (!futex_requeue_pi_prepare(this, pi_state)) {
    - /*
    - * Early woken waiter signaled that it is on the
    - * way out. Drop the pi_state reference and try the
    - * next waiter. @this->pi_state is still NULL.
    - */
    - put_pi_state(pi_state);
    - continue;
    - }
    -
    - ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
    - this->rt_waiter,
    - this->task);
    -
    - if (ret == 1) {
    - /*
    - * We got the lock. We do neither drop the refcount
    - * on pi_state nor clear this->pi_state because the
    - * waiter needs the pi_state for cleaning up the
    - * user space value. It will drop the refcount
    - * after doing so. this::requeue_state is updated
    - * in the wakeup as well.
    - */
    - requeue_pi_wake_futex(this, &key2, hb2);
    - task_count++;
    - } else if (!ret) {
    - /* Waiter is queued, move it to hb2 */
    - requeue_futex(this, hb1, hb2, &key2);
    - futex_requeue_pi_complete(this, 0);
    - task_count++;
    - } else {
    - /*
    - * rt_mutex_start_proxy_lock() detected a potential
    - * deadlock when we tried to queue that waiter.
    - * Drop the pi_state reference which we took above
    - * and remove the pointer to the state from the
    - * waiters futex_q object.
    - */
    - this->pi_state = NULL;
    - put_pi_state(pi_state);
    - futex_requeue_pi_complete(this, ret);
    - /*
    - * We stop queueing more waiters and let user space
    - * deal with the mess.
    - */
    - break;
    - }
    - }
    -
    - /*
    - * We took an extra initial reference to the pi_state in
    - * futex_proxy_trylock_atomic(). We need to drop it here again.
    - */
    - put_pi_state(pi_state);
    -
    -out_unlock:
    - double_unlock_hb(hb1, hb2);
    - wake_up_q(&wake_q);
    - hb_waiters_dec(hb2);
    - return ret ? ret : task_count;
    -}
    -
    -/* The key must be already stored in q->key. */
    -static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
    - __acquires(&hb->lock)
    -{
    - struct futex_hash_bucket *hb;
    -
    - hb = hash_futex(&q->key);
    -
    - /*
    - * Increment the counter before taking the lock so that
    - * a potential waker won't miss a to-be-slept task that is
    - * waiting for the spinlock. This is safe as all queue_lock()
    - * users end up calling queue_me(). Similarly, for housekeeping,
    - * decrement the counter at queue_unlock() when some error has
    - * occurred and we don't end up adding the task to the list.
    - */
    - hb_waiters_inc(hb); /* implies smp_mb(); (A) */
    -
    - q->lock_ptr = &hb->lock;
    -
    - spin_lock(&hb->lock);
    - return hb;
    -}
    -
    -static inline void
    -queue_unlock(struct futex_hash_bucket *hb)
    - __releases(&hb->lock)
    -{
    - spin_unlock(&hb->lock);
    - hb_waiters_dec(hb);
    -}
    -
    -static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
    -{
    - int prio;
    -
    - /*
    - * The priority used to register this element is
    - * - either the real thread-priority for the real-time threads
    - * (i.e. threads with a priority lower than MAX_RT_PRIO)
    - * - or MAX_RT_PRIO for non-RT threads.
    - * Thus, all RT-threads are woken first in priority order, and
    - * the others are woken last, in FIFO order.
    - */
    - prio = min(current->normal_prio, MAX_RT_PRIO);
    -
    - plist_node_init(&q->list, prio);
    - plist_add(&q->list, &hb->chain);
    - q->task = current;
    -}
    -
    -/**
    - * queue_me() - Enqueue the futex_q on the futex_hash_bucket
    - * @q: The futex_q to enqueue
    - * @hb: The destination hash bucket
    - *
    - * The hb->lock must be held by the caller, and is released here. A call to
    - * queue_me() is typically paired with exactly one call to unqueue_me(). The
    - * exceptions involve the PI related operations, which may use unqueue_me_pi()
    - * or nothing if the unqueue is done as part of the wake process and the unqueue
    - * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
    - * an example).
    - */
    -static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
    - __releases(&hb->lock)
    -{
    - __queue_me(q, hb);
    - spin_unlock(&hb->lock);
    -}
    -
    -/**
    - * unqueue_me() - Remove the futex_q from its futex_hash_bucket
    - * @q: The futex_q to unqueue
    - *
    - * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
    - * be paired with exactly one earlier call to queue_me().
    - *
    - * Return:
    - * - 1 - if the futex_q was still queued (and we removed unqueued it);
    - * - 0 - if the futex_q was already removed by the waking thread
    - */
    -static int unqueue_me(struct futex_q *q)
    -{
    - spinlock_t *lock_ptr;
    - int ret = 0;
    -
    - /* In the common case we don't take the spinlock, which is nice. */
    -retry:
    - /*
    - * q->lock_ptr can change between this read and the following spin_lock.
    - * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
    - * optimizing lock_ptr out of the logic below.
    - */
    - lock_ptr = READ_ONCE(q->lock_ptr);
    - if (lock_ptr != NULL) {
    - spin_lock(lock_ptr);
    - /*
    - * q->lock_ptr can change between reading it and
    - * spin_lock(), causing us to take the wrong lock. This
    - * corrects the race condition.
    - *
    - * Reasoning goes like this: if we have the wrong lock,
    - * q->lock_ptr must have changed (maybe several times)
    - * between reading it and the spin_lock(). It can
    - * change again after the spin_lock() but only if it was
    - * already changed before the spin_lock(). It cannot,
    - * however, change back to the original value. Therefore
    - * we can detect whether we acquired the correct lock.
    - */
    - if (unlikely(lock_ptr != q->lock_ptr)) {
    - spin_unlock(lock_ptr);
    - goto retry;
    - }
    - __unqueue_futex(q);
    -
    - BUG_ON(q->pi_state);
    -
    - spin_unlock(lock_ptr);
    - ret = 1;
    - }
    -
    - return ret;
    -}
    -
    -/*
    - * PI futexes can not be requeued and must remove themselves from the
    - * hash bucket. The hash bucket lock (i.e. lock_ptr) is held.
    - */
    -static void unqueue_me_pi(struct futex_q *q)
    -{
    - __unqueue_futex(q);
    -
    - BUG_ON(!q->pi_state);
    - put_pi_state(q->pi_state);
    - q->pi_state = NULL;
    -}
    -
    -static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
    - struct task_struct *argowner)
    -{
    - struct futex_pi_state *pi_state = q->pi_state;
    - struct task_struct *oldowner, *newowner;
    - u32 uval, curval, newval, newtid;
    - int err = 0;
    -
    - oldowner = pi_state->owner;
    -
    - /*
    - * We are here because either:
    - *
    - * - we stole the lock and pi_state->owner needs updating to reflect
    - * that (@argowner == current),
    - *
    - * or:
    - *
    - * - someone stole our lock and we need to fix things to point to the
    - * new owner (@argowner == NULL).
    - *
    - * Either way, we have to replace the TID in the user space variable.
    - * This must be atomic as we have to preserve the owner died bit here.
    - *
    - * Note: We write the user space value _before_ changing the pi_state
    - * because we can fault here. Imagine swapped out pages or a fork
    - * that marked all the anonymous memory readonly for cow.
    - *
    - * Modifying pi_state _before_ the user space value would leave the
    - * pi_state in an inconsistent state when we fault here, because we
    - * need to drop the locks to handle the fault. This might be observed
    - * in the PID checks when attaching to PI state .
    - */
    -retry:
    - if (!argowner) {
    - if (oldowner != current) {
    - /*
    - * We raced against a concurrent self; things are
    - * already fixed up. Nothing to do.
    - */
    - return 0;
    - }
    -
    - if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
    - /* We got the lock. pi_state is correct. Tell caller. */
    - return 1;
    - }
    -
    - /*
    - * The trylock just failed, so either there is an owner or
    - * there is a higher priority waiter than this one.
    - */
    - newowner = rt_mutex_owner(&pi_state->pi_mutex);
    - /*
    - * If the higher priority waiter has not yet taken over the
    - * rtmutex then newowner is NULL. We can't return here with
    - * that state because it's inconsistent vs. the user space
    - * state. So drop the locks and try again. It's a valid
    - * situation and not any different from the other retry
    - * conditions.
    - */
    - if (unlikely(!newowner)) {
    - err = -EAGAIN;
    - goto handle_err;
    - }
    - } else {
    - WARN_ON_ONCE(argowner != current);
    - if (oldowner == current) {
    - /*
    - * We raced against a concurrent self; things are
    - * already fixed up. Nothing to do.
    - */
    - return 1;
    - }
    - newowner = argowner;
    - }
    -
    - newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
    - /* Owner died? */
    - if (!pi_state->owner)
    - newtid |= FUTEX_OWNER_DIED;
    -
    - err = get_futex_value_locked(&uval, uaddr);
    - if (err)
    - goto handle_err;
    -
    - for (;;) {
    - newval = (uval & FUTEX_OWNER_DIED) | newtid;
    -
    - err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
    - if (err)
    - goto handle_err;
    -
    - if (curval == uval)
    - break;
    - uval = curval;
    - }
    -
    - /*
    - * We fixed up user space. Now we need to fix the pi_state
    - * itself.
    - */
    - pi_state_update_owner(pi_state, newowner);
    -
    - return argowner == current;
    -
    - /*
    - * In order to reschedule or handle a page fault, we need to drop the
    - * locks here. In the case of a fault, this gives the other task
    - * (either the highest priority waiter itself or the task which stole
    - * the rtmutex) the chance to try the fixup of the pi_state. So once we
    - * are back from handling the fault we need to check the pi_state after
    - * reacquiring the locks and before trying to do another fixup. When
    - * the fixup has been done already we simply return.
    - *
    - * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
    - * drop hb->lock since the caller owns the hb -> futex_q relation.
    - * Dropping the pi_mutex->wait_lock requires the state revalidate.
    - */
    -handle_err:
    - raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    - spin_unlock(q->lock_ptr);
    -
    - switch (err) {
    - case -EFAULT:
    - err = fault_in_user_writeable(uaddr);
    - break;
    -
    - case -EAGAIN:
    - cond_resched();
    - err = 0;
    - break;
    -
    - default:
    - WARN_ON_ONCE(1);
    - break;
    - }
    -
    - spin_lock(q->lock_ptr);
    - raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    -
    - /*
    - * Check if someone else fixed it for us:
    - */
    - if (pi_state->owner != oldowner)
    - return argowner == current;
    -
    - /* Retry if err was -EAGAIN or the fault in succeeded */
    - if (!err)
    - goto retry;
    -
    - /*
    - * fault_in_user_writeable() failed so user state is immutable. At
    - * best we can make the kernel state consistent but user state will
    - * be most likely hosed and any subsequent unlock operation will be
    - * rejected due to PI futex rule [10].
    - *
    - * Ensure that the rtmutex owner is also the pi_state owner despite
    - * the user space value claiming something different. There is no
    - * point in unlocking the rtmutex if current is the owner as it
    - * would need to wait until the next waiter has taken the rtmutex
    - * to guarantee consistent state. Keep it simple. Userspace asked
    - * for this wreckaged state.
    - *
    - * The rtmutex has an owner - either current or some other
    - * task. See the EAGAIN loop above.
    - */
    - pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
    -
    - return err;
    -}
    -
    -static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
    - struct task_struct *argowner)
    -{
    - struct futex_pi_state *pi_state = q->pi_state;
    - int ret;
    -
    - lockdep_assert_held(q->lock_ptr);
    -
    - raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    - ret = __fixup_pi_state_owner(uaddr, q, argowner);
    - raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    - return ret;
    -}
    -
    -static long futex_wait_restart(struct restart_block *restart);
    -
    -/**
    - * fixup_owner() - Post lock pi_state and corner case management
    - * @uaddr: user address of the futex
    - * @q: futex_q (contains pi_state and access to the rt_mutex)
    - * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
    - *
    - * After attempting to lock an rt_mutex, this function is called to cleanup
    - * the pi_state owner as well as handle race conditions that may allow us to
    - * acquire the lock. Must be called with the hb lock held.
    - *
    - * Return:
    - * - 1 - success, lock taken;
    - * - 0 - success, lock not taken;
    - * - <0 - on error (-EFAULT)
    - */
    -static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
    -{
    - if (locked) {
    - /*
    - * Got the lock. We might not be the anticipated owner if we
    - * did a lock-steal - fix up the PI-state in that case:
    - *
    - * Speculative pi_state->owner read (we don't hold wait_lock);
    - * since we own the lock pi_state->owner == current is the
    - * stable state, anything else needs more attention.
    - */
    - if (q->pi_state->owner != current)
    - return fixup_pi_state_owner(uaddr, q, current);
    - return 1;
    - }
    -
    - /*
    - * If we didn't get the lock; check if anybody stole it from us. In
    - * that case, we need to fix up the uval to point to them instead of
    - * us, otherwise bad things happen. [10]
    - *
    - * Another speculative read; pi_state->owner == current is unstable
    - * but needs our attention.
    - */
    - if (q->pi_state->owner == current)
    - return fixup_pi_state_owner(uaddr, q, NULL);
    -
    - /*
    - * Paranoia check. If we did not take the lock, then we should not be
    - * the owner of the rt_mutex. Warn and establish consistent state.
    - */
    - if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
    - return fixup_pi_state_owner(uaddr, q, current);
    -
    - return 0;
    -}
    -
    -/**
    - * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
    - * @hb: the futex hash bucket, must be locked by the caller
    - * @q: the futex_q to queue up on
    - * @timeout: the prepared hrtimer_sleeper, or null for no timeout
    - */
    -static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
    - struct hrtimer_sleeper *timeout)
    -{
    - /*
    - * The task state is guaranteed to be set before another task can
    - * wake it. set_current_state() is implemented using smp_store_mb() and
    - * queue_me() calls spin_unlock() upon completion, both serializing
    - * access to the hash list and forcing another memory barrier.
    - */
    - set_current_state(TASK_INTERRUPTIBLE);
    - queue_me(q, hb);
    -
    - /* Arm the timer */
    - if (timeout)
    - hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
    -
    - /*
    - * If we have been removed from the hash list, then another task
    - * has tried to wake us, and we can skip the call to schedule().
    - */
    - if (likely(!plist_node_empty(&q->list))) {
    - /*
    - * If the timer has already expired, current will already be
    - * flagged for rescheduling. Only call schedule if there
    - * is no timeout, or if it has yet to expire.
    - */
    - if (!timeout || timeout->task)
    - freezable_schedule();
    - }
    - __set_current_state(TASK_RUNNING);
    -}
    -
    -/**
    - * futex_wait_setup() - Prepare to wait on a futex
    - * @uaddr: the futex userspace address
    - * @val: the expected value
    - * @flags: futex flags (FLAGS_SHARED, etc.)
    - * @q: the associated futex_q
    - * @hb: storage for hash_bucket pointer to be returned to caller
    - *
    - * Setup the futex_q and locate the hash_bucket. Get the futex value and
    - * compare it with the expected value. Handle atomic faults internally.
    - * Return with the hb lock held on success, and unlocked on failure.
    - *
    - * Return:
    - * - 0 - uaddr contains val and hb has been locked;
    - * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
    - */
    -static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
    - struct futex_q *q, struct futex_hash_bucket **hb)
    -{
    - u32 uval;
    - int ret;
    -
    - /*
    - * Access the page AFTER the hash-bucket is locked.
    - * Order is important:
    - *
    - * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
    - * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
    - *
    - * The basic logical guarantee of a futex is that it blocks ONLY
    - * if cond(var) is known to be true at the time of blocking, for
    - * any cond. If we locked the hash-bucket after testing *uaddr, that
    - * would open a race condition where we could block indefinitely with
    - * cond(var) false, which would violate the guarantee.
    - *
    - * On the other hand, we insert q and release the hash-bucket only
    - * after testing *uaddr. This guarantees that futex_wait() will NOT
    - * absorb a wakeup if *uaddr does not match the desired values
    - * while the syscall executes.
    - */
    -retry:
    - ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
    - if (unlikely(ret != 0))
    - return ret;
    -
    -retry_private:
    - *hb = queue_lock(q);
    -
    - ret = get_futex_value_locked(&uval, uaddr);
    -
    - if (ret) {
    - queue_unlock(*hb);
    -
    - ret = get_user(uval, uaddr);
    - if (ret)
    - return ret;
    -
    - if (!(flags & FLAGS_SHARED))
    - goto retry_private;
    -
    - goto retry;
    - }
    -
    - if (uval != val) {
    - queue_unlock(*hb);
    - ret = -EWOULDBLOCK;
    - }
    -
    - return ret;
    -}
    -
    -static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
    - ktime_t *abs_time, u32 bitset)
    -{
    - struct hrtimer_sleeper timeout, *to;
    - struct restart_block *restart;
    - struct futex_hash_bucket *hb;
    - struct futex_q q = futex_q_init;
    - int ret;
    -
    - if (!bitset)
    - return -EINVAL;
    - q.bitset = bitset;
    -
    - to = futex_setup_timer(abs_time, &timeout, flags,
    - current->timer_slack_ns);
    -retry:
    - /*
    - * Prepare to wait on uaddr. On success, it holds hb->lock and q
    - * is initialized.
    - */
    - ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
    - if (ret)
    - goto out;
    -
    - /* queue_me and wait for wakeup, timeout, or a signal. */
    - futex_wait_queue_me(hb, &q, to);
    -
    - /* If we were woken (and unqueued), we succeeded, whatever. */
    - ret = 0;
    - if (!unqueue_me(&q))
    - goto out;
    - ret = -ETIMEDOUT;
    - if (to && !to->task)
    - goto out;
    -
    - /*
    - * We expect signal_pending(current), but we might be the
    - * victim of a spurious wakeup as well.
    - */
    - if (!signal_pending(current))
    - goto retry;
    -
    - ret = -ERESTARTSYS;
    - if (!abs_time)
    - goto out;
    -
    - restart = &current->restart_block;
    - restart->futex.uaddr = uaddr;
    - restart->futex.val = val;
    - restart->futex.time = *abs_time;
    - restart->futex.bitset = bitset;
    - restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
    -
    - ret = set_restart_fn(restart, futex_wait_restart);
    -
    -out:
    - if (to) {
    - hrtimer_cancel(&to->timer);
    - destroy_hrtimer_on_stack(&to->timer);
    - }
    - return ret;
    -}
    -
    -
    -static long futex_wait_restart(struct restart_block *restart)
    -{
    - u32 __user *uaddr = restart->futex.uaddr;
    - ktime_t t, *tp = NULL;
    -
    - if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
    - t = restart->futex.time;
    - tp = &t;
    - }
    - restart->fn = do_no_restart_syscall;
    -
    - return (long)futex_wait(uaddr, restart->futex.flags,
    - restart->futex.val, tp, restart->futex.bitset);
    -}
    -
    -
    -/*
    - * Userspace tried a 0 -> TID atomic transition of the futex value
    - * and failed. The kernel side here does the whole locking operation:
    - * if there are waiters then it will block as a consequence of relying
    - * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
    - * a 0 value of the futex too.).
    - *
    - * Also serves as futex trylock_pi()'ing, and due semantics.
    - */
    -static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
    - ktime_t *time, int trylock)
    -{
    - struct hrtimer_sleeper timeout, *to;
    - struct task_struct *exiting = NULL;
    - struct rt_mutex_waiter rt_waiter;
    - struct futex_hash_bucket *hb;
    - struct futex_q q = futex_q_init;
    - int res, ret;
    -
    - if (!IS_ENABLED(CONFIG_FUTEX_PI))
    - return -ENOSYS;
    -
    - if (refill_pi_state_cache())
    - return -ENOMEM;
    -
    - to = futex_setup_timer(time, &timeout, flags, 0);
    -
    -retry:
    - ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
    - if (unlikely(ret != 0))
    - goto out;
    -
    -retry_private:
    - hb = queue_lock(&q);
    -
    - ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
    - &exiting, 0);
    - if (unlikely(ret)) {
    - /*
    - * Atomic work succeeded and we got the lock,
    - * or failed. Either way, we do _not_ block.
    - */
    - switch (ret) {
    - case 1:
    - /* We got the lock. */
    - ret = 0;
    - goto out_unlock_put_key;
    - case -EFAULT:
    - goto uaddr_faulted;
    - case -EBUSY:
    - case -EAGAIN:
    - /*
    - * Two reasons for this:
    - * - EBUSY: Task is exiting and we just wait for the
    - * exit to complete.
    - * - EAGAIN: The user space value changed.
    - */
    - queue_unlock(hb);
    - /*
    - * Handle the case where the owner is in the middle of
    - * exiting. Wait for the exit to complete otherwise
    - * this task might loop forever, aka. live lock.
    - */
    - wait_for_owner_exiting(ret, exiting);
    - cond_resched();
    - goto retry;
    - default:
    - goto out_unlock_put_key;
    - }
    - }
    -
    - WARN_ON(!q.pi_state);
    -
    - /*
    - * Only actually queue now that the atomic ops are done:
    - */
    - __queue_me(&q, hb);
    -
    - if (trylock) {
    - ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
    - /* Fixup the trylock return value: */
    - ret = ret ? 0 : -EWOULDBLOCK;
    - goto no_block;
    - }
    -
    - rt_mutex_init_waiter(&rt_waiter);
    -
    - /*
    - * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
    - * hold it while doing rt_mutex_start_proxy(), because then it will
    - * include hb->lock in the blocking chain, even through we'll not in
    - * fact hold it while blocking. This will lead it to report -EDEADLK
    - * and BUG when futex_unlock_pi() interleaves with this.
    - *
    - * Therefore acquire wait_lock while holding hb->lock, but drop the
    - * latter before calling __rt_mutex_start_proxy_lock(). This
    - * interleaves with futex_unlock_pi() -- which does a similar lock
    - * handoff -- such that the latter can observe the futex_q::pi_state
    - * before __rt_mutex_start_proxy_lock() is done.
    - */
    - raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
    - spin_unlock(q.lock_ptr);
    - /*
    - * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
    - * such that futex_unlock_pi() is guaranteed to observe the waiter when
    - * it sees the futex_q::pi_state.
    - */
    - ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
    - raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
    -
    - if (ret) {
    - if (ret == 1)
    - ret = 0;
    - goto cleanup;
    - }
    -
    - if (unlikely(to))
    - hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
    -
    - ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
    -
    -cleanup:
    - spin_lock(q.lock_ptr);
    - /*
    - * If we failed to acquire the lock (deadlock/signal/timeout), we must
    - * first acquire the hb->lock before removing the lock from the
    - * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
    - * lists consistent.
    - *
    - * In particular; it is important that futex_unlock_pi() can not
    - * observe this inconsistency.
    - */
    - if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
    - ret = 0;
    -
    -no_block:
    - /*
    - * Fixup the pi_state owner and possibly acquire the lock if we
    - * haven't already.
    - */
    - res = fixup_owner(uaddr, &q, !ret);
    - /*
    - * If fixup_owner() returned an error, propagate that. If it acquired
    - * the lock, clear our -ETIMEDOUT or -EINTR.
    - */
    - if (res)
    - ret = (res < 0) ? res : 0;
    -
    - unqueue_me_pi(&q);
    - spin_unlock(q.lock_ptr);
    - goto out;
    -
    -out_unlock_put_key:
    - queue_unlock(hb);
    -
    -out:
    - if (to) {
    - hrtimer_cancel(&to->timer);
    - destroy_hrtimer_on_stack(&to->timer);
    - }
    - return ret != -EINTR ? ret : -ERESTARTNOINTR;
    -
    -uaddr_faulted:
    - queue_unlock(hb);
    -
    - ret = fault_in_user_writeable(uaddr);
    - if (ret)
    - goto out;
    -
    - if (!(flags & FLAGS_SHARED))
    - goto retry_private;
    -
    - goto retry;
    -}
    -
    -/*
    - * Userspace attempted a TID -> 0 atomic transition, and failed.
    - * This is the in-kernel slowpath: we look up the PI state (if any),
    - * and do the rt-mutex unlock.
    - */
    -static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
    -{
    - u32 curval, uval, vpid = task_pid_vnr(current);
    - union futex_key key = FUTEX_KEY_INIT;
    - struct futex_hash_bucket *hb;
    - struct futex_q *top_waiter;
    - int ret;
    -
    - if (!IS_ENABLED(CONFIG_FUTEX_PI))
    - return -ENOSYS;
    -
    -retry:
    - if (get_user(uval, uaddr))
    - return -EFAULT;
    - /*
    - * We release only a lock we actually own:
    - */
    - if ((uval & FUTEX_TID_MASK) != vpid)
    - return -EPERM;
    -
    - ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
    - if (ret)
    - return ret;
    -
    - hb = hash_futex(&key);
    - spin_lock(&hb->lock);
    -
    - /*
    - * Check waiters first. We do not trust user space values at
    - * all and we at least want to know if user space fiddled
    - * with the futex value instead of blindly unlocking.
    - */
    - top_waiter = futex_top_waiter(hb, &key);
    - if (top_waiter) {
    - struct futex_pi_state *pi_state = top_waiter->pi_state;
    -
    - ret = -EINVAL;
    - if (!pi_state)
    - goto out_unlock;
    -
    - /*
    - * If current does not own the pi_state then the futex is
    - * inconsistent and user space fiddled with the futex value.
    - */
    - if (pi_state->owner != current)
    - goto out_unlock;
    -
    - get_pi_state(pi_state);
    - /*
    - * By taking wait_lock while still holding hb->lock, we ensure
    - * there is no point where we hold neither; and therefore
    - * wake_futex_pi() must observe a state consistent with what we
    - * observed.
    - *
    - * In particular; this forces __rt_mutex_start_proxy() to
    - * complete such that we're guaranteed to observe the
    - * rt_waiter. Also see the WARN in wake_futex_pi().
    - */
    - raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    - spin_unlock(&hb->lock);
    -
    - /* drops pi_state->pi_mutex.wait_lock */
    - ret = wake_futex_pi(uaddr, uval, pi_state);
    -
    - put_pi_state(pi_state);
    -
    - /*
    - * Success, we're done! No tricky corner cases.
    - */
    - if (!ret)
    - return ret;
    - /*
    - * The atomic access to the futex value generated a
    - * pagefault, so retry the user-access and the wakeup:
    - */
    - if (ret == -EFAULT)
    - goto pi_faulted;
    - /*
    - * A unconditional UNLOCK_PI op raced against a waiter
    - * setting the FUTEX_WAITERS bit. Try again.
    - */
    - if (ret == -EAGAIN)
    - goto pi_retry;
    - /*
    - * wake_futex_pi has detected invalid state. Tell user
    - * space.
    - */
    - return ret;
    - }
    -
    - /*
    - * We have no kernel internal state, i.e. no waiters in the
    - * kernel. Waiters which are about to queue themselves are stuck
    - * on hb->lock. So we can safely ignore them. We do neither
    - * preserve the WAITERS bit not the OWNER_DIED one. We are the
    - * owner.
    - */
    - if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
    - spin_unlock(&hb->lock);
    - switch (ret) {
    - case -EFAULT:
    - goto pi_faulted;
    -
    - case -EAGAIN:
    - goto pi_retry;
    -
    - default:
    - WARN_ON_ONCE(1);
    - return ret;
    - }
    - }
    -
    - /*
    - * If uval has changed, let user space handle it.
    - */
    - ret = (curval == uval) ? 0 : -EAGAIN;
    -
    -out_unlock:
    - spin_unlock(&hb->lock);
    - return ret;
    -
    -pi_retry:
    - cond_resched();
    - goto retry;
    -
    -pi_faulted:
    -
    - ret = fault_in_user_writeable(uaddr);
    - if (!ret)
    - goto retry;
    -
    - return ret;
    -}
    -
    -/**
    - * handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex
    - * @hb: the hash_bucket futex_q was original enqueued on
    - * @q: the futex_q woken while waiting to be requeued
    - * @timeout: the timeout associated with the wait (NULL if none)
    - *
    - * Determine the cause for the early wakeup.
    - *
    - * Return:
    - * -EWOULDBLOCK or -ETIMEDOUT or -ERESTARTNOINTR
    - */
    -static inline
    -int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
    - struct futex_q *q,
    - struct hrtimer_sleeper *timeout)
    -{
    - int ret;
    -
    - /*
    - * With the hb lock held, we avoid races while we process the wakeup.
    - * We only need to hold hb (and not hb2) to ensure atomicity as the
    - * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
    - * It can't be requeued from uaddr2 to something else since we don't
    - * support a PI aware source futex for requeue.
    - */
    - WARN_ON_ONCE(&hb->lock != q->lock_ptr);
    -
    - /*
    - * We were woken prior to requeue by a timeout or a signal.
    - * Unqueue the futex_q and determine which it was.
    - */
    - plist_del(&q->list, &hb->chain);
    - hb_waiters_dec(hb);
    -
    - /* Handle spurious wakeups gracefully */
    - ret = -EWOULDBLOCK;
    - if (timeout && !timeout->task)
    - ret = -ETIMEDOUT;
    - else if (signal_pending(current))
    - ret = -ERESTARTNOINTR;
    - return ret;
    -}
    -
    -/**
    - * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
    - * @uaddr: the futex we initially wait on (non-pi)
    - * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
    - * the same type, no requeueing from private to shared, etc.
    - * @val: the expected value of uaddr
    - * @abs_time: absolute timeout
    - * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
    - * @uaddr2: the pi futex we will take prior to returning to user-space
    - *
    - * The caller will wait on uaddr and will be requeued by futex_requeue() to
    - * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
    - * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
    - * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
    - * without one, the pi logic would not know which task to boost/deboost, if
    - * there was a need to.
    - *
    - * We call schedule in futex_wait_queue_me() when we enqueue and return there
    - * via the following--
    - * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
    - * 2) wakeup on uaddr2 after a requeue
    - * 3) signal
    - * 4) timeout
    - *
    - * If 3, cleanup and return -ERESTARTNOINTR.
    - *
    - * If 2, we may then block on trying to take the rt_mutex and return via:
    - * 5) successful lock
    - * 6) signal
    - * 7) timeout
    - * 8) other lock acquisition failure
    - *
    - * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
    - *
    - * If 4 or 7, we cleanup and return with -ETIMEDOUT.
    - *
    - * Return:
    - * - 0 - On success;
    - * - <0 - On error
    - */
    -static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
    - u32 val, ktime_t *abs_time, u32 bitset,
    - u32 __user *uaddr2)
    -{
    - struct hrtimer_sleeper timeout, *to;
    - struct rt_mutex_waiter rt_waiter;
    - struct futex_hash_bucket *hb;
    - union futex_key key2 = FUTEX_KEY_INIT;
    - struct futex_q q = futex_q_init;
    - struct rt_mutex_base *pi_mutex;
    - int res, ret;
    -
    - if (!IS_ENABLED(CONFIG_FUTEX_PI))
    - return -ENOSYS;
    -
    - if (uaddr == uaddr2)
    - return -EINVAL;
    -
    - if (!bitset)
    - return -EINVAL;
    -
    - to = futex_setup_timer(abs_time, &timeout, flags,
    - current->timer_slack_ns);
    -
    - /*
    - * The waiter is allocated on our stack, manipulated by the requeue
    - * code while we sleep on uaddr.
    - */
    - rt_mutex_init_waiter(&rt_waiter);
    -
    - ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
    - if (unlikely(ret != 0))
    - goto out;
    -
    - q.bitset = bitset;
    - q.rt_waiter = &rt_waiter;
    - q.requeue_pi_key = &key2;
    -
    - /*
    - * Prepare to wait on uaddr. On success, it holds hb->lock and q
    - * is initialized.
    - */
    - ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
    - if (ret)
    - goto out;
    -
    - /*
    - * The check above which compares uaddrs is not sufficient for
    - * shared futexes. We need to compare the keys:
    - */
    - if (match_futex(&q.key, &key2)) {
    - queue_unlock(hb);
    - ret = -EINVAL;
    - goto out;
    - }
    -
    - /* Queue the futex_q, drop the hb lock, wait for wakeup. */
    - futex_wait_queue_me(hb, &q, to);
    -
    - switch (futex_requeue_pi_wakeup_sync(&q)) {
    - case Q_REQUEUE_PI_IGNORE:
    - /* The waiter is still on uaddr1 */
    - spin_lock(&hb->lock);
    - ret = handle_early_requeue_pi_wakeup(hb, &q, to);
    - spin_unlock(&hb->lock);
    - break;
    -
    - case Q_REQUEUE_PI_LOCKED:
    - /* The requeue acquired the lock */
    - if (q.pi_state && (q.pi_state->owner != current)) {
    - spin_lock(q.lock_ptr);
    - ret = fixup_owner(uaddr2, &q, true);
    - /*
    - * Drop the reference to the pi state which the
    - * requeue_pi() code acquired for us.
    - */
    - put_pi_state(q.pi_state);
    - spin_unlock(q.lock_ptr);
    - /*
    - * Adjust the return value. It's either -EFAULT or
    - * success (1) but the caller expects 0 for success.
    - */
    - ret = ret < 0 ? ret : 0;
    - }
    - break;
    -
    - case Q_REQUEUE_PI_DONE:
    - /* Requeue completed. Current is 'pi_blocked_on' the rtmutex */
    - pi_mutex = &q.pi_state->pi_mutex;
    - ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
    -
    - /* Current is not longer pi_blocked_on */
    - spin_lock(q.lock_ptr);
    - if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
    - ret = 0;
    -
    - debug_rt_mutex_free_waiter(&rt_waiter);
    - /*
    - * Fixup the pi_state owner and possibly acquire the lock if we
    - * haven't already.
    - */
    - res = fixup_owner(uaddr2, &q, !ret);
    - /*
    - * If fixup_owner() returned an error, propagate that. If it
    - * acquired the lock, clear -ETIMEDOUT or -EINTR.
    - */
    - if (res)
    - ret = (res < 0) ? res : 0;
    -
    - unqueue_me_pi(&q);
    - spin_unlock(q.lock_ptr);
    -
    - if (ret == -EINTR) {
    - /*
    - * We've already been requeued, but cannot restart
    - * by calling futex_lock_pi() directly. We could
    - * restart this syscall, but it would detect that
    - * the user space "val" changed and return
    - * -EWOULDBLOCK. Save the overhead of the restart
    - * and return -EWOULDBLOCK directly.
    - */
    - ret = -EWOULDBLOCK;
    - }
    - break;
    - default:
    - BUG();
    - }
    -
    -out:
    - if (to) {
    - hrtimer_cancel(&to->timer);
    - destroy_hrtimer_on_stack(&to->timer);
    - }
    - return ret;
    -}
    -
    -/*
    - * Support for robust futexes: the kernel cleans up held futexes at
    - * thread exit time.
    - *
    - * Implementation: user-space maintains a per-thread list of locks it
    - * is holding. Upon do_exit(), the kernel carefully walks this list,
    - * and marks all locks that are owned by this thread with the
    - * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
    - * always manipulated with the lock held, so the list is private and
    - * per-thread. Userspace also maintains a per-thread 'list_op_pending'
    - * field, to allow the kernel to clean up if the thread dies after
    - * acquiring the lock, but just before it could have added itself to
    - * the list. There can only be one such pending lock.
    - */
    -
    -/**
    - * sys_set_robust_list() - Set the robust-futex list head of a task
    - * @head: pointer to the list-head
    - * @len: length of the list-head, as userspace expects
    - */
    -SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
    - size_t, len)
    -{
    - if (!futex_cmpxchg_enabled)
    - return -ENOSYS;
    - /*
    - * The kernel knows only one size for now:
    - */
    - if (unlikely(len != sizeof(*head)))
    - return -EINVAL;
    -
    - current->robust_list = head;
    -
    - return 0;
    -}
    -
    -/**
    - * sys_get_robust_list() - Get the robust-futex list head of a task
    - * @pid: pid of the process [zero for current task]
    - * @head_ptr: pointer to a list-head pointer, the kernel fills it in
    - * @len_ptr: pointer to a length field, the kernel fills in the header size
    - */
    -SYSCALL_DEFINE3(get_robust_list, int, pid,
    - struct robust_list_head __user * __user *, head_ptr,
    - size_t __user *, len_ptr)
    -{
    - struct robust_list_head __user *head;
    - unsigned long ret;
    - struct task_struct *p;
    -
    - if (!futex_cmpxchg_enabled)
    - return -ENOSYS;
    -
    - rcu_read_lock();
    -
    - ret = -ESRCH;
    - if (!pid)
    - p = current;
    - else {
    - p = find_task_by_vpid(pid);
    - if (!p)
    - goto err_unlock;
    - }
    -
    - ret = -EPERM;
    - if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
    - goto err_unlock;
    -
    - head = p->robust_list;
    - rcu_read_unlock();
    -
    - if (put_user(sizeof(*head), len_ptr))
    - return -EFAULT;
    - return put_user(head, head_ptr);
    -
    -err_unlock:
    - rcu_read_unlock();
    -
    - return ret;
    -}
    -
    -/* Constants for the pending_op argument of handle_futex_death */
    -#define HANDLE_DEATH_PENDING true
    -#define HANDLE_DEATH_LIST false
    -
    -/*
    - * Process a futex-list entry, check whether it's owned by the
    - * dying task, and do notification if so:
    - */
    -static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
    - bool pi, bool pending_op)
    -{
    - u32 uval, nval, mval;
    - int err;
    -
    - /* Futex address must be 32bit aligned */
    - if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
    - return -1;
    -
    -retry:
    - if (get_user(uval, uaddr))
    - return -1;
    -
    - /*
    - * Special case for regular (non PI) futexes. The unlock path in
    - * user space has two race scenarios:
    - *
    - * 1. The unlock path releases the user space futex value and
    - * before it can execute the futex() syscall to wake up
    - * waiters it is killed.
    - *
    - * 2. A woken up waiter is killed before it can acquire the
    - * futex in user space.
    - *
    - * In both cases the TID validation below prevents a wakeup of
    - * potential waiters which can cause these waiters to block
    - * forever.
    - *
    - * In both cases the following conditions are met:
    - *
    - * 1) task->robust_list->list_op_pending != NULL
    - * @pending_op == true
    - * 2) User space futex value == 0
    - * 3) Regular futex: @pi == false
    - *
    - * If these conditions are met, it is safe to attempt waking up a
    - * potential waiter without touching the user space futex value and
    - * trying to set the OWNER_DIED bit. The user space futex value is
    - * uncontended and the rest of the user space mutex state is
    - * consistent, so a woken waiter will just take over the
    - * uncontended futex. Setting the OWNER_DIED bit would create
    - * inconsistent state and malfunction of the user space owner died
    - * handling.
    - */
    - if (pending_op && !pi && !uval) {
    - futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
    - return 0;
    - }
    -
    - if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
    - return 0;
    -
    - /*
    - * Ok, this dying thread is truly holding a futex
    - * of interest. Set the OWNER_DIED bit atomically
    - * via cmpxchg, and if the value had FUTEX_WAITERS
    - * set, wake up a waiter (if any). (We have to do a
    - * futex_wake() even if OWNER_DIED is already set -
    - * to handle the rare but possible case of recursive
    - * thread-death.) The rest of the cleanup is done in
    - * userspace.
    - */
    - mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
    -
    - /*
    - * We are not holding a lock here, but we want to have
    - * the pagefault_disable/enable() protection because
    - * we want to handle the fault gracefully. If the
    - * access fails we try to fault in the futex with R/W
    - * verification via get_user_pages. get_user() above
    - * does not guarantee R/W access. If that fails we
    - * give up and leave the futex locked.
    - */
    - if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
    - switch (err) {
    - case -EFAULT:
    - if (fault_in_user_writeable(uaddr))
    - return -1;
    - goto retry;
    -
    - case -EAGAIN:
    - cond_resched();
    - goto retry;
    -
    - default:
    - WARN_ON_ONCE(1);
    - return err;
    - }
    - }
    -
    - if (nval != uval)
    - goto retry;
    -
    - /*
    - * Wake robust non-PI futexes here. The wakeup of
    - * PI futexes happens in exit_pi_state():
    - */
    - if (!pi && (uval & FUTEX_WAITERS))
    - futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
    -
    - return 0;
    -}
    -
    -/*
    - * Fetch a robust-list pointer. Bit 0 signals PI futexes:
    - */
    -static inline int fetch_robust_entry(struct robust_list __user **entry,
    - struct robust_list __user * __user *head,
    - unsigned int *pi)
    -{
    - unsigned long uentry;
    -
    - if (get_user(uentry, (unsigned long __user *)head))
    - return -EFAULT;
    -
    - *entry = (void __user *)(uentry & ~1UL);
    - *pi = uentry & 1;
    -
    - return 0;
    -}
    -
    -/*
    - * Walk curr->robust_list (very carefully, it's a userspace list!)
    - * and mark any locks found there dead, and notify any waiters.
    - *
    - * We silently return on any sign of list-walking problem.
    - */
    -static void exit_robust_list(struct task_struct *curr)
    -{
    - struct robust_list_head __user *head = curr->robust_list;
    - struct robust_list __user *entry, *next_entry, *pending;
    - unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
    - unsigned int next_pi;
    - unsigned long futex_offset;
    - int rc;
    -
    - if (!futex_cmpxchg_enabled)
    - return;
    -
    - /*
    - * Fetch the list head (which was registered earlier, via
    - * sys_set_robust_list()):
    - */
    - if (fetch_robust_entry(&entry, &head->list.next, &pi))
    - return;
    - /*
    - * Fetch the relative futex offset:
    - */
    - if (get_user(futex_offset, &head->futex_offset))
    - return;
    - /*
    - * Fetch any possibly pending lock-add first, and handle it
    - * if it exists:
    - */
    - if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
    - return;
    -
    - next_entry = NULL; /* avoid warning with gcc */
    - while (entry != &head->list) {
    - /*
    - * Fetch the next entry in the list before calling
    - * handle_futex_death:
    - */
    - rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
    - /*
    - * A pending lock might already be on the list, so
    - * don't process it twice:
    - */
    - if (entry != pending) {
    - if (handle_futex_death((void __user *)entry + futex_offset,
    - curr, pi, HANDLE_DEATH_LIST))
    - return;
    - }
    - if (rc)
    - return;
    - entry = next_entry;
    - pi = next_pi;
    - /*
    - * Avoid excessively long or circular lists:
    - */
    - if (!--limit)
    - break;
    -
    - cond_resched();
    - }
    -
    - if (pending) {
    - handle_futex_death((void __user *)pending + futex_offset,
    - curr, pip, HANDLE_DEATH_PENDING);
    - }
    -}
    -
    -static void futex_cleanup(struct task_struct *tsk)
    -{
    - if (unlikely(tsk->robust_list)) {
    - exit_robust_list(tsk);
    - tsk->robust_list = NULL;
    - }
    -
    -#ifdef CONFIG_COMPAT
    - if (unlikely(tsk->compat_robust_list)) {
    - compat_exit_robust_list(tsk);
    - tsk->compat_robust_list = NULL;
    - }
    -#endif
    -
    - if (unlikely(!list_empty(&tsk->pi_state_list)))
    - exit_pi_state_list(tsk);
    -}
    -
    -/**
    - * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
    - * @tsk: task to set the state on
    - *
    - * Set the futex exit state of the task lockless. The futex waiter code
    - * observes that state when a task is exiting and loops until the task has
    - * actually finished the futex cleanup. The worst case for this is that the
    - * waiter runs through the wait loop until the state becomes visible.
    - *
    - * This is called from the recursive fault handling path in do_exit().
    - *
    - * This is best effort. Either the futex exit code has run already or
    - * not. If the OWNER_DIED bit has been set on the futex then the waiter can
    - * take it over. If not, the problem is pushed back to user space. If the
    - * futex exit code did not run yet, then an already queued waiter might
    - * block forever, but there is nothing which can be done about that.
    - */
    -void futex_exit_recursive(struct task_struct *tsk)
    -{
    - /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
    - if (tsk->futex_state == FUTEX_STATE_EXITING)
    - mutex_unlock(&tsk->futex_exit_mutex);
    - tsk->futex_state = FUTEX_STATE_DEAD;
    -}
    -
    -static void futex_cleanup_begin(struct task_struct *tsk)
    -{
    - /*
    - * Prevent various race issues against a concurrent incoming waiter
    - * including live locks by forcing the waiter to block on
    - * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
    - * attach_to_pi_owner().
    - */
    - mutex_lock(&tsk->futex_exit_mutex);
    -
    - /*
    - * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
    - *
    - * This ensures that all subsequent checks of tsk->futex_state in
    - * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
    - * tsk->pi_lock held.
    - *
    - * It guarantees also that a pi_state which was queued right before
    - * the state change under tsk->pi_lock by a concurrent waiter must
    - * be observed in exit_pi_state_list().
    - */
    - raw_spin_lock_irq(&tsk->pi_lock);
    - tsk->futex_state = FUTEX_STATE_EXITING;
    - raw_spin_unlock_irq(&tsk->pi_lock);
    -}
    -
    -static void futex_cleanup_end(struct task_struct *tsk, int state)
    -{
    - /*
    - * Lockless store. The only side effect is that an observer might
    - * take another loop until it becomes visible.
    - */
    - tsk->futex_state = state;
    - /*
    - * Drop the exit protection. This unblocks waiters which observed
    - * FUTEX_STATE_EXITING to reevaluate the state.
    - */
    - mutex_unlock(&tsk->futex_exit_mutex);
    -}
    -
    -void futex_exec_release(struct task_struct *tsk)
    -{
    - /*
    - * The state handling is done for consistency, but in the case of
    - * exec() there is no way to prevent further damage as the PID stays
    - * the same. But for the unlikely and arguably buggy case that a
    - * futex is held on exec(), this provides at least as much state
    - * consistency protection which is possible.
    - */
    - futex_cleanup_begin(tsk);
    - futex_cleanup(tsk);
    - /*
    - * Reset the state to FUTEX_STATE_OK. The task is alive and about
    - * exec a new binary.
    - */
    - futex_cleanup_end(tsk, FUTEX_STATE_OK);
    -}
    -
    -void futex_exit_release(struct task_struct *tsk)
    -{
    - futex_cleanup_begin(tsk);
    - futex_cleanup(tsk);
    - futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
    -}
    -
    -long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
    - u32 __user *uaddr2, u32 val2, u32 val3)
    -{
    - int cmd = op & FUTEX_CMD_MASK;
    - unsigned int flags = 0;
    -
    - if (!(op & FUTEX_PRIVATE_FLAG))
    - flags |= FLAGS_SHARED;
    -
    - if (op & FUTEX_CLOCK_REALTIME) {
    - flags |= FLAGS_CLOCKRT;
    - if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
    - cmd != FUTEX_LOCK_PI2)
    - return -ENOSYS;
    - }
    -
    - switch (cmd) {
    - case FUTEX_LOCK_PI:
    - case FUTEX_LOCK_PI2:
    - case FUTEX_UNLOCK_PI:
    - case FUTEX_TRYLOCK_PI:
    - case FUTEX_WAIT_REQUEUE_PI:
    - case FUTEX_CMP_REQUEUE_PI:
    - if (!futex_cmpxchg_enabled)
    - return -ENOSYS;
    - }
    -
    - switch (cmd) {
    - case FUTEX_WAIT:
    - val3 = FUTEX_BITSET_MATCH_ANY;
    - fallthrough;
    - case FUTEX_WAIT_BITSET:
    - return futex_wait(uaddr, flags, val, timeout, val3);
    - case FUTEX_WAKE:
    - val3 = FUTEX_BITSET_MATCH_ANY;
    - fallthrough;
    - case FUTEX_WAKE_BITSET:
    - return futex_wake(uaddr, flags, val, val3);
    - case FUTEX_REQUEUE:
    - return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
    - case FUTEX_CMP_REQUEUE:
    - return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
    - case FUTEX_WAKE_OP:
    - return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
    - case FUTEX_LOCK_PI:
    - flags |= FLAGS_CLOCKRT;
    - fallthrough;
    - case FUTEX_LOCK_PI2:
    - return futex_lock_pi(uaddr, flags, timeout, 0);
    - case FUTEX_UNLOCK_PI:
    - return futex_unlock_pi(uaddr, flags);
    - case FUTEX_TRYLOCK_PI:
    - return futex_lock_pi(uaddr, flags, NULL, 1);
    - case FUTEX_WAIT_REQUEUE_PI:
    - val3 = FUTEX_BITSET_MATCH_ANY;
    - return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
    - uaddr2);
    - case FUTEX_CMP_REQUEUE_PI:
    - return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
    - }
    - return -ENOSYS;
    -}
    -
    -static __always_inline bool futex_cmd_has_timeout(u32 cmd)
    -{
    - switch (cmd) {
    - case FUTEX_WAIT:
    - case FUTEX_LOCK_PI:
    - case FUTEX_LOCK_PI2:
    - case FUTEX_WAIT_BITSET:
    - case FUTEX_WAIT_REQUEUE_PI:
    - return true;
    - }
    - return false;
    -}
    -
    -static __always_inline int
    -futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
    -{
    - if (!timespec64_valid(ts))
    - return -EINVAL;
    -
    - *t = timespec64_to_ktime(*ts);
    - if (cmd == FUTEX_WAIT)
    - *t = ktime_add_safe(ktime_get(), *t);
    - else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
    - *t = timens_ktime_to_host(CLOCK_MONOTONIC, *t);
    - return 0;
    -}
    -
    -SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
    - const struct __kernel_timespec __user *, utime,
    - u32 __user *, uaddr2, u32, val3)
    -{
    - int ret, cmd = op & FUTEX_CMD_MASK;
    - ktime_t t, *tp = NULL;
    - struct timespec64 ts;
    -
    - if (utime && futex_cmd_has_timeout(cmd)) {
    - if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
    - return -EFAULT;
    - if (get_timespec64(&ts, utime))
    - return -EFAULT;
    - ret = futex_init_timeout(cmd, op, &ts, &t);
    - if (ret)
    - return ret;
    - tp = &t;
    - }
    -
    - return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
    -}
    -
    -#ifdef CONFIG_COMPAT
    -/*
    - * Fetch a robust-list pointer. Bit 0 signals PI futexes:
    - */
    -static inline int
    -compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
    - compat_uptr_t __user *head, unsigned int *pi)
    -{
    - if (get_user(*uentry, head))
    - return -EFAULT;
    -
    - *entry = compat_ptr((*uentry) & ~1);
    - *pi = (unsigned int)(*uentry) & 1;
    -
    - return 0;
    -}
    -
    -static void __user *futex_uaddr(struct robust_list __user *entry,
    - compat_long_t futex_offset)
    -{
    - compat_uptr_t base = ptr_to_compat(entry);
    - void __user *uaddr = compat_ptr(base + futex_offset);
    -
    - return uaddr;
    -}
    -
    -/*
    - * Walk curr->robust_list (very carefully, it's a userspace list!)
    - * and mark any locks found there dead, and notify any waiters.
    - *
    - * We silently return on any sign of list-walking problem.
    - */
    -static void compat_exit_robust_list(struct task_struct *curr)
    -{
    - struct compat_robust_list_head __user *head = curr->compat_robust_list;
    - struct robust_list __user *entry, *next_entry, *pending;
    - unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
    - unsigned int next_pi;
    - compat_uptr_t uentry, next_uentry, upending;
    - compat_long_t futex_offset;
    - int rc;
    -
    - if (!futex_cmpxchg_enabled)
    - return;
    -
    - /*
    - * Fetch the list head (which was registered earlier, via
    - * sys_set_robust_list()):
    - */
    - if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
    - return;
    - /*
    - * Fetch the relative futex offset:
    - */
    - if (get_user(futex_offset, &head->futex_offset))
    - return;
    - /*
    - * Fetch any possibly pending lock-add first, and handle it
    - * if it exists:
    - */
    - if (compat_fetch_robust_entry(&upending, &pending,
    - &head->list_op_pending, &pip))
    - return;
    -
    - next_entry = NULL; /* avoid warning with gcc */
    - while (entry != (struct robust_list __user *) &head->list) {
    - /*
    - * Fetch the next entry in the list before calling
    - * handle_futex_death:
    - */
    - rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
    - (compat_uptr_t __user *)&entry->next, &next_pi);
    - /*
    - * A pending lock might already be on the list, so
    - * dont process it twice:
    - */
    - if (entry != pending) {
    - void __user *uaddr = futex_uaddr(entry, futex_offset);
    -
    - if (handle_futex_death(uaddr, curr, pi,
    - HANDLE_DEATH_LIST))
    - return;
    - }
    - if (rc)
    - return;
    - uentry = next_uentry;
    - entry = next_entry;
    - pi = next_pi;
    - /*
    - * Avoid excessively long or circular lists:
    - */
    - if (!--limit)
    - break;
    -
    - cond_resched();
    - }
    - if (pending) {
    - void __user *uaddr = futex_uaddr(pending, futex_offset);
    -
    - handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
    - }
    -}
    -
    -COMPAT_SYSCALL_DEFINE2(set_robust_list,
    - struct compat_robust_list_head __user *, head,
    - compat_size_t, len)
    -{
    - if (!futex_cmpxchg_enabled)
    - return -ENOSYS;
    -
    - if (unlikely(len != sizeof(*head)))
    - return -EINVAL;
    -
    - current->compat_robust_list = head;
    -
    - return 0;
    -}
    -
    -COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
    - compat_uptr_t __user *, head_ptr,
    - compat_size_t __user *, len_ptr)
    -{
    - struct compat_robust_list_head __user *head;
    - unsigned long ret;
    - struct task_struct *p;
    -
    - if (!futex_cmpxchg_enabled)
    - return -ENOSYS;
    -
    - rcu_read_lock();
    -
    - ret = -ESRCH;
    - if (!pid)
    - p = current;
    - else {
    - p = find_task_by_vpid(pid);
    - if (!p)
    - goto err_unlock;
    - }
    -
    - ret = -EPERM;
    - if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
    - goto err_unlock;
    -
    - head = p->compat_robust_list;
    - rcu_read_unlock();
    -
    - if (put_user(sizeof(*head), len_ptr))
    - return -EFAULT;
    - return put_user(ptr_to_compat(head), head_ptr);
    -
    -err_unlock:
    - rcu_read_unlock();
    -
    - return ret;
    -}
    -#endif /* CONFIG_COMPAT */
    -
    -#ifdef CONFIG_COMPAT_32BIT_TIME
    -SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
    - const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
    - u32, val3)
    -{
    - int ret, cmd = op & FUTEX_CMD_MASK;
    - ktime_t t, *tp = NULL;
    - struct timespec64 ts;
    -
    - if (utime && futex_cmd_has_timeout(cmd)) {
    - if (get_old_timespec32(&ts, utime))
    - return -EFAULT;
    - ret = futex_init_timeout(cmd, op, &ts, &t);
    - if (ret)
    - return ret;
    - tp = &t;
    - }
    -
    - return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
    -}
    -#endif /* CONFIG_COMPAT_32BIT_TIME */
    -
    -static void __init futex_detect_cmpxchg(void)
    -{
    -#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
    - u32 curval;
    -
    - /*
    - * This will fail and we want it. Some arch implementations do
    - * runtime detection of the futex_atomic_cmpxchg_inatomic()
    - * functionality. We want to know that before we call in any
    - * of the complex code paths. Also we want to prevent
    - * registration of robust lists in that case. NULL is
    - * guaranteed to fault and we get -EFAULT on functional
    - * implementation, the non-functional ones will return
    - * -ENOSYS.
    - */
    - if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
    - futex_cmpxchg_enabled = 1;
    -#endif
    -}
    -
    -static int __init futex_init(void)
    -{
    - unsigned int futex_shift;
    - unsigned long i;
    -
    -#if CONFIG_BASE_SMALL
    - futex_hashsize = 16;
    -#else
    - futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
    -#endif
    -
    - futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
    - futex_hashsize, 0,
    - futex_hashsize < 256 ? HASH_SMALL : 0,
    - &futex_shift, NULL,
    - futex_hashsize, futex_hashsize);
    - futex_hashsize = 1UL << futex_shift;
    -
    - futex_detect_cmpxchg();
    -
    - for (i = 0; i < futex_hashsize; i++) {
    - atomic_set(&futex_queues[i].waiters, 0);
    - plist_head_init(&futex_queues[i].chain);
    - spin_lock_init(&futex_queues[i].lock);
    - }
    -
    - return 0;
    -}
    -core_initcall(futex_init);
    diff --git a/kernel/futex/Makefile b/kernel/futex/Makefile
    new file mode 100644
    index 0000000..b89ba3f
    --- /dev/null
    +++ b/kernel/futex/Makefile
    @@ -0,0 +1,3 @@
    +# SPDX-License-Identifier: GPL-2.0
    +
    +obj-y += core.o
    diff --git a/kernel/futex/core.c b/kernel/futex/core.c
    new file mode 100644
    index 0000000..f9bc9aa
    --- /dev/null
    +++ b/kernel/futex/core.c
    @@ -0,0 +1,4272 @@
    +// SPDX-License-Identifier: GPL-2.0-or-later
    +/*
    + * Fast Userspace Mutexes (which I call "Futexes!").
    + * (C) Rusty Russell, IBM 2002
    + *
    + * Generalized futexes, futex requeueing, misc fixes by Ingo Molnar
    + * (C) Copyright 2003 Red Hat Inc, All Rights Reserved
    + *
    + * Removed page pinning, fix privately mapped COW pages and other cleanups
    + * (C) Copyright 2003, 2004 Jamie Lokier
    + *
    + * Robust futex support started by Ingo Molnar
    + * (C) Copyright 2006 Red Hat Inc, All Rights Reserved
    + * Thanks to Thomas Gleixner for suggestions, analysis and fixes.
    + *
    + * PI-futex support started by Ingo Molnar and Thomas Gleixner
    + * Copyright (C) 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
    + * Copyright (C) 2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
    + *
    + * PRIVATE futexes by Eric Dumazet
    + * Copyright (C) 2007 Eric Dumazet <dada1@cosmosbay.com>
    + *
    + * Requeue-PI support by Darren Hart <dvhltc@us.ibm.com>
    + * Copyright (C) IBM Corporation, 2009
    + * Thanks to Thomas Gleixner for conceptual design and careful reviews.
    + *
    + * Thanks to Ben LaHaise for yelling "hashed waitqueues" loudly
    + * enough at me, Linus for the original (flawed) idea, Matthew
    + * Kirkwood for proof-of-concept implementation.
    + *
    + * "The futexes are also cursed."
    + * "But they come in a choice of three flavours!"
    + */
    +#include <linux/compat.h>
    +#include <linux/jhash.h>
    +#include <linux/pagemap.h>
    +#include <linux/syscalls.h>
    +#include <linux/freezer.h>
    +#include <linux/memblock.h>
    +#include <linux/fault-inject.h>
    +#include <linux/time_namespace.h>
    +
    +#include <asm/futex.h>
    +
    +#include "../locking/rtmutex_common.h"
    +
    +/*
    + * READ this before attempting to hack on futexes!
    + *
    + * Basic futex operation and ordering guarantees
    + * =============================================
    + *
    + * The waiter reads the futex value in user space and calls
    + * futex_wait(). This function computes the hash bucket and acquires
    + * the hash bucket lock. After that it reads the futex user space value
    + * again and verifies that the data has not changed. If it has not changed
    + * it enqueues itself into the hash bucket, releases the hash bucket lock
    + * and schedules.
    + *
    + * The waker side modifies the user space value of the futex and calls
    + * futex_wake(). This function computes the hash bucket and acquires the
    + * hash bucket lock. Then it looks for waiters on that futex in the hash
    + * bucket and wakes them.
    + *
    + * In futex wake up scenarios where no tasks are blocked on a futex, taking
    + * the hb spinlock can be avoided and simply return. In order for this
    + * optimization to work, ordering guarantees must exist so that the waiter
    + * being added to the list is acknowledged when the list is concurrently being
    + * checked by the waker, avoiding scenarios like the following:
    + *
    + * CPU 0 CPU 1
    + * val = *futex;
    + * sys_futex(WAIT, futex, val);
    + * futex_wait(futex, val);
    + * uval = *futex;
    + * *futex = newval;
    + * sys_futex(WAKE, futex);
    + * futex_wake(futex);
    + * if (queue_empty())
    + * return;
    + * if (uval == val)
    + * lock(hash_bucket(futex));
    + * queue();
    + * unlock(hash_bucket(futex));
    + * schedule();
    + *
    + * This would cause the waiter on CPU 0 to wait forever because it
    + * missed the transition of the user space value from val to newval
    + * and the waker did not find the waiter in the hash bucket queue.
    + *
    + * The correct serialization ensures that a waiter either observes
    + * the changed user space value before blocking or is woken by a
    + * concurrent waker:
    + *
    + * CPU 0 CPU 1
    + * val = *futex;
    + * sys_futex(WAIT, futex, val);
    + * futex_wait(futex, val);
    + *
    + * waiters++; (a)
    + * smp_mb(); (A) <-- paired with -.
    + * |
    + * lock(hash_bucket(futex)); |
    + * |
    + * uval = *futex; |
    + * | *futex = newval;
    + * | sys_futex(WAKE, futex);
    + * | futex_wake(futex);
    + * |
    + * `--------> smp_mb(); (B)
    + * if (uval == val)
    + * queue();
    + * unlock(hash_bucket(futex));
    + * schedule(); if (waiters)
    + * lock(hash_bucket(futex));
    + * else wake_waiters(futex);
    + * waiters--; (b) unlock(hash_bucket(futex));
    + *
    + * Where (A) orders the waiters increment and the futex value read through
    + * atomic operations (see hb_waiters_inc) and where (B) orders the write
    + * to futex and the waiters read (see hb_waiters_pending()).
    + *
    + * This yields the following case (where X:=waiters, Y:=futex):
    + *
    + * X = Y = 0
    + *
    + * w[X]=1 w[Y]=1
    + * MB MB
    + * r[Y]=y r[X]=x
    + *
    + * Which guarantees that x==0 && y==0 is impossible; which translates back into
    + * the guarantee that we cannot both miss the futex variable change and the
    + * enqueue.
    + *
    + * Note that a new waiter is accounted for in (a) even when it is possible that
    + * the wait call can return error, in which case we backtrack from it in (b).
    + * Refer to the comment in queue_lock().
    + *
    + * Similarly, in order to account for waiters being requeued on another
    + * address we always increment the waiters for the destination bucket before
    + * acquiring the lock. It then decrements them again after releasing it -
    + * the code that actually moves the futex(es) between hash buckets (requeue_futex)
    + * will do the additional required waiter count housekeeping. This is done for
    + * double_lock_hb() and double_unlock_hb(), respectively.
    + */
    +
    +#ifdef CONFIG_HAVE_FUTEX_CMPXCHG
    +#define futex_cmpxchg_enabled 1
    +#else
    +static int __read_mostly futex_cmpxchg_enabled;
    +#endif
    +
    +/*
    + * Futex flags used to encode options to functions and preserve them across
    + * restarts.
    + */
    +#ifdef CONFIG_MMU
    +# define FLAGS_SHARED 0x01
    +#else
    +/*
    + * NOMMU does not have per process address space. Let the compiler optimize
    + * code away.
    + */
    +# define FLAGS_SHARED 0x00
    +#endif
    +#define FLAGS_CLOCKRT 0x02
    +#define FLAGS_HAS_TIMEOUT 0x04
    +
    +/*
    + * Priority Inheritance state:
    + */
    +struct futex_pi_state {
    + /*
    + * list of 'owned' pi_state instances - these have to be
    + * cleaned up in do_exit() if the task exits prematurely:
    + */
    + struct list_head list;
    +
    + /*
    + * The PI object:
    + */
    + struct rt_mutex_base pi_mutex;
    +
    + struct task_struct *owner;
    + refcount_t refcount;
    +
    + union futex_key key;
    +} __randomize_layout;
    +
    +/**
    + * struct futex_q - The hashed futex queue entry, one per waiting task
    + * @list: priority-sorted list of tasks waiting on this futex
    + * @task: the task waiting on the futex
    + * @lock_ptr: the hash bucket lock
    + * @key: the key the futex is hashed on
    + * @pi_state: optional priority inheritance state
    + * @rt_waiter: rt_waiter storage for use with requeue_pi
    + * @requeue_pi_key: the requeue_pi target futex key
    + * @bitset: bitset for the optional bitmasked wakeup
    + * @requeue_state: State field for futex_requeue_pi()
    + * @requeue_wait: RCU wait for futex_requeue_pi() (RT only)
    + *
    + * We use this hashed waitqueue, instead of a normal wait_queue_entry_t, so
    + * we can wake only the relevant ones (hashed queues may be shared).
    + *
    + * A futex_q has a woken state, just like tasks have TASK_RUNNING.
    + * It is considered woken when plist_node_empty(&q->list) || q->lock_ptr == 0.
    + * The order of wakeup is always to make the first condition true, then
    + * the second.
    + *
    + * PI futexes are typically woken before they are removed from the hash list via
    + * the rt_mutex code. See unqueue_me_pi().
    + */
    +struct futex_q {
    + struct plist_node list;
    +
    + struct task_struct *task;
    + spinlock_t *lock_ptr;
    + union futex_key key;
    + struct futex_pi_state *pi_state;
    + struct rt_mutex_waiter *rt_waiter;
    + union futex_key *requeue_pi_key;
    + u32 bitset;
    + atomic_t requeue_state;
    +#ifdef CONFIG_PREEMPT_RT
    + struct rcuwait requeue_wait;
    +#endif
    +} __randomize_layout;
    +
    +/*
    + * On PREEMPT_RT, the hash bucket lock is a 'sleeping' spinlock with an
    + * underlying rtmutex. The task which is about to be requeued could have
    + * just woken up (timeout, signal). After the wake up the task has to
    + * acquire hash bucket lock, which is held by the requeue code. As a task
    + * can only be blocked on _ONE_ rtmutex at a time, the proxy lock blocking
    + * and the hash bucket lock blocking would collide and corrupt state.
    + *
    + * On !PREEMPT_RT this is not a problem and everything could be serialized
    + * on hash bucket lock, but aside of having the benefit of common code,
    + * this allows to avoid doing the requeue when the task is already on the
    + * way out and taking the hash bucket lock of the original uaddr1 when the
    + * requeue has been completed.
    + *
    + * The following state transitions are valid:
    + *
    + * On the waiter side:
    + * Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_IGNORE
    + * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_WAIT
    + *
    + * On the requeue side:
    + * Q_REQUEUE_PI_NONE -> Q_REQUEUE_PI_INPROGRESS
    + * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_DONE/LOCKED
    + * Q_REQUEUE_PI_IN_PROGRESS -> Q_REQUEUE_PI_NONE (requeue failed)
    + * Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_DONE/LOCKED
    + * Q_REQUEUE_PI_WAIT -> Q_REQUEUE_PI_IGNORE (requeue failed)
    + *
    + * The requeue side ignores a waiter with state Q_REQUEUE_PI_IGNORE as this
    + * signals that the waiter is already on the way out. It also means that
    + * the waiter is still on the 'wait' futex, i.e. uaddr1.
    + *
    + * The waiter side signals early wakeup to the requeue side either through
    + * setting state to Q_REQUEUE_PI_IGNORE or to Q_REQUEUE_PI_WAIT depending
    + * on the current state. In case of Q_REQUEUE_PI_IGNORE it can immediately
    + * proceed to take the hash bucket lock of uaddr1. If it set state to WAIT,
    + * which means the wakeup is interleaving with a requeue in progress it has
    + * to wait for the requeue side to change the state. Either to DONE/LOCKED
    + * or to IGNORE. DONE/LOCKED means the waiter q is now on the uaddr2 futex
    + * and either blocked (DONE) or has acquired it (LOCKED). IGNORE is set by
    + * the requeue side when the requeue attempt failed via deadlock detection
    + * and therefore the waiter q is still on the uaddr1 futex.
    + */
    +enum {
    + Q_REQUEUE_PI_NONE = 0,
    + Q_REQUEUE_PI_IGNORE,
    + Q_REQUEUE_PI_IN_PROGRESS,
    + Q_REQUEUE_PI_WAIT,
    + Q_REQUEUE_PI_DONE,
    + Q_REQUEUE_PI_LOCKED,
    +};
    +
    +static const struct futex_q futex_q_init = {
    + /* list gets initialized in queue_me()*/
    + .key = FUTEX_KEY_INIT,
    + .bitset = FUTEX_BITSET_MATCH_ANY,
    + .requeue_state = ATOMIC_INIT(Q_REQUEUE_PI_NONE),
    +};
    +
    +/*
    + * Hash buckets are shared by all the futex_keys that hash to the same
    + * location. Each key may have multiple futex_q structures, one for each task
    + * waiting on a futex.
    + */
    +struct futex_hash_bucket {
    + atomic_t waiters;
    + spinlock_t lock;
    + struct plist_head chain;
    +} ____cacheline_aligned_in_smp;
    +
    +/*
    + * The base of the bucket array and its size are always used together
    + * (after initialization only in hash_futex()), so ensure that they
    + * reside in the same cacheline.
    + */
    +static struct {
    + struct futex_hash_bucket *queues;
    + unsigned long hashsize;
    +} __futex_data __read_mostly __aligned(2*sizeof(long));
    +#define futex_queues (__futex_data.queues)
    +#define futex_hashsize (__futex_data.hashsize)
    +
    +
    +/*
    + * Fault injections for futexes.
    + */
    +#ifdef CONFIG_FAIL_FUTEX
    +
    +static struct {
    + struct fault_attr attr;
    +
    + bool ignore_private;
    +} fail_futex = {
    + .attr = FAULT_ATTR_INITIALIZER,
    + .ignore_private = false,
    +};
    +
    +static int __init setup_fail_futex(char *str)
    +{
    + return setup_fault_attr(&fail_futex.attr, str);
    +}
    +__setup("fail_futex=", setup_fail_futex);
    +
    +static bool should_fail_futex(bool fshared)
    +{
    + if (fail_futex.ignore_private && !fshared)
    + return false;
    +
    + return should_fail(&fail_futex.attr, 1);
    +}
    +
    +#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
    +
    +static int __init fail_futex_debugfs(void)
    +{
    + umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
    + struct dentry *dir;
    +
    + dir = fault_create_debugfs_attr("fail_futex", NULL,
    + &fail_futex.attr);
    + if (IS_ERR(dir))
    + return PTR_ERR(dir);
    +
    + debugfs_create_bool("ignore-private", mode, dir,
    + &fail_futex.ignore_private);
    + return 0;
    +}
    +
    +late_initcall(fail_futex_debugfs);
    +
    +#endif /* CONFIG_FAULT_INJECTION_DEBUG_FS */
    +
    +#else
    +static inline bool should_fail_futex(bool fshared)
    +{
    + return false;
    +}
    +#endif /* CONFIG_FAIL_FUTEX */
    +
    +#ifdef CONFIG_COMPAT
    +static void compat_exit_robust_list(struct task_struct *curr);
    +#endif
    +
    +/*
    + * Reflects a new waiter being added to the waitqueue.
    + */
    +static inline void hb_waiters_inc(struct futex_hash_bucket *hb)
    +{
    +#ifdef CONFIG_SMP
    + atomic_inc(&hb->waiters);
    + /*
    + * Full barrier (A), see the ordering comment above.
    + */
    + smp_mb__after_atomic();
    +#endif
    +}
    +
    +/*
    + * Reflects a waiter being removed from the waitqueue by wakeup
    + * paths.
    + */
    +static inline void hb_waiters_dec(struct futex_hash_bucket *hb)
    +{
    +#ifdef CONFIG_SMP
    + atomic_dec(&hb->waiters);
    +#endif
    +}
    +
    +static inline int hb_waiters_pending(struct futex_hash_bucket *hb)
    +{
    +#ifdef CONFIG_SMP
    + /*
    + * Full barrier (B), see the ordering comment above.
    + */
    + smp_mb();
    + return atomic_read(&hb->waiters);
    +#else
    + return 1;
    +#endif
    +}
    +
    +/**
    + * hash_futex - Return the hash bucket in the global hash
    + * @key: Pointer to the futex key for which the hash is calculated
    + *
    + * We hash on the keys returned from get_futex_key (see below) and return the
    + * corresponding hash bucket in the global hash.
    + */
    +static struct futex_hash_bucket *hash_futex(union futex_key *key)
    +{
    + u32 hash = jhash2((u32 *)key, offsetof(typeof(*key), both.offset) / 4,
    + key->both.offset);
    +
    + return &futex_queues[hash & (futex_hashsize - 1)];
    +}
    +
    +
    +/**
    + * match_futex - Check whether two futex keys are equal
    + * @key1: Pointer to key1
    + * @key2: Pointer to key2
    + *
    + * Return 1 if two futex_keys are equal, 0 otherwise.
    + */
    +static inline int match_futex(union futex_key *key1, union futex_key *key2)
    +{
    + return (key1 && key2
    + && key1->both.word == key2->both.word
    + && key1->both.ptr == key2->both.ptr
    + && key1->both.offset == key2->both.offset);
    +}
    +
    +enum futex_access {
    + FUTEX_READ,
    + FUTEX_WRITE
    +};
    +
    +/**
    + * futex_setup_timer - set up the sleeping hrtimer.
    + * @time: ptr to the given timeout value
    + * @timeout: the hrtimer_sleeper structure to be set up
    + * @flags: futex flags
    + * @range_ns: optional range in ns
    + *
    + * Return: Initialized hrtimer_sleeper structure or NULL if no timeout
    + * value given
    + */
    +static inline struct hrtimer_sleeper *
    +futex_setup_timer(ktime_t *time, struct hrtimer_sleeper *timeout,
    + int flags, u64 range_ns)
    +{
    + if (!time)
    + return NULL;
    +
    + hrtimer_init_sleeper_on_stack(timeout, (flags & FLAGS_CLOCKRT) ?
    + CLOCK_REALTIME : CLOCK_MONOTONIC,
    + HRTIMER_MODE_ABS);
    + /*
    + * If range_ns is 0, calling hrtimer_set_expires_range_ns() is
    + * effectively the same as calling hrtimer_set_expires().
    + */
    + hrtimer_set_expires_range_ns(&timeout->timer, *time, range_ns);
    +
    + return timeout;
    +}
    +
    +/*
    + * Generate a machine wide unique identifier for this inode.
    + *
    + * This relies on u64 not wrapping in the life-time of the machine; which with
    + * 1ns resolution means almost 585 years.
    + *
    + * This further relies on the fact that a well formed program will not unmap
    + * the file while it has a (shared) futex waiting on it. This mapping will have
    + * a file reference which pins the mount and inode.
    + *
    + * If for some reason an inode gets evicted and read back in again, it will get
    + * a new sequence number and will _NOT_ match, even though it is the exact same
    + * file.
    + *
    + * It is important that match_futex() will never have a false-positive, esp.
    + * for PI futexes that can mess up the state. The above argues that false-negatives
    + * are only possible for malformed programs.
    + */
    +static u64 get_inode_sequence_number(struct inode *inode)
    +{
    + static atomic64_t i_seq;
    + u64 old;
    +
    + /* Does the inode already have a sequence number? */
    + old = atomic64_read(&inode->i_sequence);
    + if (likely(old))
    + return old;
    +
    + for (;;) {
    + u64 new = atomic64_add_return(1, &i_seq);
    + if (WARN_ON_ONCE(!new))
    + continue;
    +
    + old = atomic64_cmpxchg_relaxed(&inode->i_sequence, 0, new);
    + if (old)
    + return old;
    + return new;
    + }
    +}
    +
    +/**
    + * get_futex_key() - Get parameters which are the keys for a futex
    + * @uaddr: virtual address of the futex
    + * @fshared: false for a PROCESS_PRIVATE futex, true for PROCESS_SHARED
    + * @key: address where result is stored.
    + * @rw: mapping needs to be read/write (values: FUTEX_READ,
    + * FUTEX_WRITE)
    + *
    + * Return: a negative error code or 0
    + *
    + * The key words are stored in @key on success.
    + *
    + * For shared mappings (when @fshared), the key is:
    + *
    + * ( inode->i_sequence, page->index, offset_within_page )
    + *
    + * [ also see get_inode_sequence_number() ]
    + *
    + * For private mappings (or when !@fshared), the key is:
    + *
    + * ( current->mm, address, 0 )
    + *
    + * This allows (cross process, where applicable) identification of the futex
    + * without keeping the page pinned for the duration of the FUTEX_WAIT.
    + *
    + * lock_page() might sleep, the caller should not hold a spinlock.
    + */
    +static int get_futex_key(u32 __user *uaddr, bool fshared, union futex_key *key,
    + enum futex_access rw)
    +{
    + unsigned long address = (unsigned long)uaddr;
    + struct mm_struct *mm = current->mm;
    + struct page *page, *tail;
    + struct address_space *mapping;
    + int err, ro = 0;
    +
    + /*
    + * The futex address must be "naturally" aligned.
    + */
    + key->both.offset = address % PAGE_SIZE;
    + if (unlikely((address % sizeof(u32)) != 0))
    + return -EINVAL;
    + address -= key->both.offset;
    +
    + if (unlikely(!access_ok(uaddr, sizeof(u32))))
    + return -EFAULT;
    +
    + if (unlikely(should_fail_futex(fshared)))
    + return -EFAULT;
    +
    + /*
    + * PROCESS_PRIVATE futexes are fast.
    + * As the mm cannot disappear under us and the 'key' only needs
    + * virtual address, we dont even have to find the underlying vma.
    + * Note : We do have to check 'uaddr' is a valid user address,
    + * but access_ok() should be faster than find_vma()
    + */
    + if (!fshared) {
    + key->private.mm = mm;
    + key->private.address = address;
    + return 0;
    + }
    +
    +again:
    + /* Ignore any VERIFY_READ mapping (futex common case) */
    + if (unlikely(should_fail_futex(true)))
    + return -EFAULT;
    +
    + err = get_user_pages_fast(address, 1, FOLL_WRITE, &page);
    + /*
    + * If write access is not required (eg. FUTEX_WAIT), try
    + * and get read-only access.
    + */
    + if (err == -EFAULT && rw == FUTEX_READ) {
    + err = get_user_pages_fast(address, 1, 0, &page);
    + ro = 1;
    + }
    + if (err < 0)
    + return err;
    + else
    + err = 0;
    +
    + /*
    + * The treatment of mapping from this point on is critical. The page
    + * lock protects many things but in this context the page lock
    + * stabilizes mapping, prevents inode freeing in the shared
    + * file-backed region case and guards against movement to swap cache.
    + *
    + * Strictly speaking the page lock is not needed in all cases being
    + * considered here and page lock forces unnecessarily serialization
    + * From this point on, mapping will be re-verified if necessary and
    + * page lock will be acquired only if it is unavoidable
    + *
    + * Mapping checks require the head page for any compound page so the
    + * head page and mapping is looked up now. For anonymous pages, it
    + * does not matter if the page splits in the future as the key is
    + * based on the address. For filesystem-backed pages, the tail is
    + * required as the index of the page determines the key. For
    + * base pages, there is no tail page and tail == page.
    + */
    + tail = page;
    + page = compound_head(page);
    + mapping = READ_ONCE(page->mapping);
    +
    + /*
    + * If page->mapping is NULL, then it cannot be a PageAnon
    + * page; but it might be the ZERO_PAGE or in the gate area or
    + * in a special mapping (all cases which we are happy to fail);
    + * or it may have been a good file page when get_user_pages_fast
    + * found it, but truncated or holepunched or subjected to
    + * invalidate_complete_page2 before we got the page lock (also
    + * cases which we are happy to fail). And we hold a reference,
    + * so refcount care in invalidate_complete_page's remove_mapping
    + * prevents drop_caches from setting mapping to NULL beneath us.
    + *
    + * The case we do have to guard against is when memory pressure made
    + * shmem_writepage move it from filecache to swapcache beneath us:
    + * an unlikely race, but we do need to retry for page->mapping.
    + */
    + if (unlikely(!mapping)) {
    + int shmem_swizzled;
    +
    + /*
    + * Page lock is required to identify which special case above
    + * applies. If this is really a shmem page then the page lock
    + * will prevent unexpected transitions.
    + */
    + lock_page(page);
    + shmem_swizzled = PageSwapCache(page) || page->mapping;
    + unlock_page(page);
    + put_page(page);
    +
    + if (shmem_swizzled)
    + goto again;
    +
    + return -EFAULT;
    + }
    +
    + /*
    + * Private mappings are handled in a simple way.
    + *
    + * If the futex key is stored on an anonymous page, then the associated
    + * object is the mm which is implicitly pinned by the calling process.
    + *
    + * NOTE: When userspace waits on a MAP_SHARED mapping, even if
    + * it's a read-only handle, it's expected that futexes attach to
    + * the object not the particular process.
    + */
    + if (PageAnon(page)) {
    + /*
    + * A RO anonymous page will never change and thus doesn't make
    + * sense for futex operations.
    + */
    + if (unlikely(should_fail_futex(true)) || ro) {
    + err = -EFAULT;
    + goto out;
    + }
    +
    + key->both.offset |= FUT_OFF_MMSHARED; /* ref taken on mm */
    + key->private.mm = mm;
    + key->private.address = address;
    +
    + } else {
    + struct inode *inode;
    +
    + /*
    + * The associated futex object in this case is the inode and
    + * the page->mapping must be traversed. Ordinarily this should
    + * be stabilised under page lock but it's not strictly
    + * necessary in this case as we just want to pin the inode, not
    + * update the radix tree or anything like that.
    + *
    + * The RCU read lock is taken as the inode is finally freed
    + * under RCU. If the mapping still matches expectations then the
    + * mapping->host can be safely accessed as being a valid inode.
    + */
    + rcu_read_lock();
    +
    + if (READ_ONCE(page->mapping) != mapping) {
    + rcu_read_unlock();
    + put_page(page);
    +
    + goto again;
    + }
    +
    + inode = READ_ONCE(mapping->host);
    + if (!inode) {
    + rcu_read_unlock();
    + put_page(page);
    +
    + goto again;
    + }
    +
    + key->both.offset |= FUT_OFF_INODE; /* inode-based key */
    + key->shared.i_seq = get_inode_sequence_number(inode);
    + key->shared.pgoff = page_to_pgoff(tail);
    + rcu_read_unlock();
    + }
    +
    +out:
    + put_page(page);
    + return err;
    +}
    +
    +/**
    + * fault_in_user_writeable() - Fault in user address and verify RW access
    + * @uaddr: pointer to faulting user space address
    + *
    + * Slow path to fixup the fault we just took in the atomic write
    + * access to @uaddr.
    + *
    + * We have no generic implementation of a non-destructive write to the
    + * user address. We know that we faulted in the atomic pagefault
    + * disabled section so we can as well avoid the #PF overhead by
    + * calling get_user_pages() right away.
    + */
    +static int fault_in_user_writeable(u32 __user *uaddr)
    +{
    + struct mm_struct *mm = current->mm;
    + int ret;
    +
    + mmap_read_lock(mm);
    + ret = fixup_user_fault(mm, (unsigned long)uaddr,
    + FAULT_FLAG_WRITE, NULL);
    + mmap_read_unlock(mm);
    +
    + return ret < 0 ? ret : 0;
    +}
    +
    +/**
    + * futex_top_waiter() - Return the highest priority waiter on a futex
    + * @hb: the hash bucket the futex_q's reside in
    + * @key: the futex key (to distinguish it from other futex futex_q's)
    + *
    + * Must be called with the hb lock held.
    + */
    +static struct futex_q *futex_top_waiter(struct futex_hash_bucket *hb,
    + union futex_key *key)
    +{
    + struct futex_q *this;
    +
    + plist_for_each_entry(this, &hb->chain, list) {
    + if (match_futex(&this->key, key))
    + return this;
    + }
    + return NULL;
    +}
    +
    +static int cmpxchg_futex_value_locked(u32 *curval, u32 __user *uaddr,
    + u32 uval, u32 newval)
    +{
    + int ret;
    +
    + pagefault_disable();
    + ret = futex_atomic_cmpxchg_inatomic(curval, uaddr, uval, newval);
    + pagefault_enable();
    +
    + return ret;
    +}
    +
    +static int get_futex_value_locked(u32 *dest, u32 __user *from)
    +{
    + int ret;
    +
    + pagefault_disable();
    + ret = __get_user(*dest, from);
    + pagefault_enable();
    +
    + return ret ? -EFAULT : 0;
    +}
    +
    +
    +/*
    + * PI code:
    + */
    +static int refill_pi_state_cache(void)
    +{
    + struct futex_pi_state *pi_state;
    +
    + if (likely(current->pi_state_cache))
    + return 0;
    +
    + pi_state = kzalloc(sizeof(*pi_state), GFP_KERNEL);
    +
    + if (!pi_state)
    + return -ENOMEM;
    +
    + INIT_LIST_HEAD(&pi_state->list);
    + /* pi_mutex gets initialized later */
    + pi_state->owner = NULL;
    + refcount_set(&pi_state->refcount, 1);
    + pi_state->key = FUTEX_KEY_INIT;
    +
    + current->pi_state_cache = pi_state;
    +
    + return 0;
    +}
    +
    +static struct futex_pi_state *alloc_pi_state(void)
    +{
    + struct futex_pi_state *pi_state = current->pi_state_cache;
    +
    + WARN_ON(!pi_state);
    + current->pi_state_cache = NULL;
    +
    + return pi_state;
    +}
    +
    +static void pi_state_update_owner(struct futex_pi_state *pi_state,
    + struct task_struct *new_owner)
    +{
    + struct task_struct *old_owner = pi_state->owner;
    +
    + lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
    +
    + if (old_owner) {
    + raw_spin_lock(&old_owner->pi_lock);
    + WARN_ON(list_empty(&pi_state->list));
    + list_del_init(&pi_state->list);
    + raw_spin_unlock(&old_owner->pi_lock);
    + }
    +
    + if (new_owner) {
    + raw_spin_lock(&new_owner->pi_lock);
    + WARN_ON(!list_empty(&pi_state->list));
    + list_add(&pi_state->list, &new_owner->pi_state_list);
    + pi_state->owner = new_owner;
    + raw_spin_unlock(&new_owner->pi_lock);
    + }
    +}
    +
    +static void get_pi_state(struct futex_pi_state *pi_state)
    +{
    + WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
    +}
    +
    +/*
    + * Drops a reference to the pi_state object and frees or caches it
    + * when the last reference is gone.
    + */
    +static void put_pi_state(struct futex_pi_state *pi_state)
    +{
    + if (!pi_state)
    + return;
    +
    + if (!refcount_dec_and_test(&pi_state->refcount))
    + return;
    +
    + /*
    + * If pi_state->owner is NULL, the owner is most probably dying
    + * and has cleaned up the pi_state already
    + */
    + if (pi_state->owner) {
    + unsigned long flags;
    +
    + raw_spin_lock_irqsave(&pi_state->pi_mutex.wait_lock, flags);
    + pi_state_update_owner(pi_state, NULL);
    + rt_mutex_proxy_unlock(&pi_state->pi_mutex);
    + raw_spin_unlock_irqrestore(&pi_state->pi_mutex.wait_lock, flags);
    + }
    +
    + if (current->pi_state_cache) {
    + kfree(pi_state);
    + } else {
    + /*
    + * pi_state->list is already empty.
    + * clear pi_state->owner.
    + * refcount is at 0 - put it back to 1.
    + */
    + pi_state->owner = NULL;
    + refcount_set(&pi_state->refcount, 1);
    + current->pi_state_cache = pi_state;
    + }
    +}
    +
    +#ifdef CONFIG_FUTEX_PI
    +
    +/*
    + * This task is holding PI mutexes at exit time => bad.
    + * Kernel cleans up PI-state, but userspace is likely hosed.
    + * (Robust-futex cleanup is separate and might save the day for userspace.)
    + */
    +static void exit_pi_state_list(struct task_struct *curr)
    +{
    + struct list_head *next, *head = &curr->pi_state_list;
    + struct futex_pi_state *pi_state;
    + struct futex_hash_bucket *hb;
    + union futex_key key = FUTEX_KEY_INIT;
    +
    + if (!futex_cmpxchg_enabled)
    + return;
    + /*
    + * We are a ZOMBIE and nobody can enqueue itself on
    + * pi_state_list anymore, but we have to be careful
    + * versus waiters unqueueing themselves:
    + */
    + raw_spin_lock_irq(&curr->pi_lock);
    + while (!list_empty(head)) {
    + next = head->next;
    + pi_state = list_entry(next, struct futex_pi_state, list);
    + key = pi_state->key;
    + hb = hash_futex(&key);
    +
    + /*
    + * We can race against put_pi_state() removing itself from the
    + * list (a waiter going away). put_pi_state() will first
    + * decrement the reference count and then modify the list, so
    + * its possible to see the list entry but fail this reference
    + * acquire.
    + *
    + * In that case; drop the locks to let put_pi_state() make
    + * progress and retry the loop.
    + */
    + if (!refcount_inc_not_zero(&pi_state->refcount)) {
    + raw_spin_unlock_irq(&curr->pi_lock);
    + cpu_relax();
    + raw_spin_lock_irq(&curr->pi_lock);
    + continue;
    + }
    + raw_spin_unlock_irq(&curr->pi_lock);
    +
    + spin_lock(&hb->lock);
    + raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    + raw_spin_lock(&curr->pi_lock);
    + /*
    + * We dropped the pi-lock, so re-check whether this
    + * task still owns the PI-state:
    + */
    + if (head->next != next) {
    + /* retain curr->pi_lock for the loop invariant */
    + raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
    + spin_unlock(&hb->lock);
    + put_pi_state(pi_state);
    + continue;
    + }
    +
    + WARN_ON(pi_state->owner != curr);
    + WARN_ON(list_empty(&pi_state->list));
    + list_del_init(&pi_state->list);
    + pi_state->owner = NULL;
    +
    + raw_spin_unlock(&curr->pi_lock);
    + raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    + spin_unlock(&hb->lock);
    +
    + rt_mutex_futex_unlock(&pi_state->pi_mutex);
    + put_pi_state(pi_state);
    +
    + raw_spin_lock_irq(&curr->pi_lock);
    + }
    + raw_spin_unlock_irq(&curr->pi_lock);
    +}
    +#else
    +static inline void exit_pi_state_list(struct task_struct *curr) { }
    +#endif
    +
    +/*
    + * We need to check the following states:
    + *
    + * Waiter | pi_state | pi->owner | uTID | uODIED | ?
    + *
    + * [1] NULL | --- | --- | 0 | 0/1 | Valid
    + * [2] NULL | --- | --- | >0 | 0/1 | Valid
    + *
    + * [3] Found | NULL | -- | Any | 0/1 | Invalid
    + *
    + * [4] Found | Found | NULL | 0 | 1 | Valid
    + * [5] Found | Found | NULL | >0 | 1 | Invalid
    + *
    + * [6] Found | Found | task | 0 | 1 | Valid
    + *
    + * [7] Found | Found | NULL | Any | 0 | Invalid
    + *
    + * [8] Found | Found | task | ==taskTID | 0/1 | Valid
    + * [9] Found | Found | task | 0 | 0 | Invalid
    + * [10] Found | Found | task | !=taskTID | 0/1 | Invalid
    + *
    + * [1] Indicates that the kernel can acquire the futex atomically. We
    + * came here due to a stale FUTEX_WAITERS/FUTEX_OWNER_DIED bit.
    + *
    + * [2] Valid, if TID does not belong to a kernel thread. If no matching
    + * thread is found then it indicates that the owner TID has died.
    + *
    + * [3] Invalid. The waiter is queued on a non PI futex
    + *
    + * [4] Valid state after exit_robust_list(), which sets the user space
    + * value to FUTEX_WAITERS | FUTEX_OWNER_DIED.
    + *
    + * [5] The user space value got manipulated between exit_robust_list()
    + * and exit_pi_state_list()
    + *
    + * [6] Valid state after exit_pi_state_list() which sets the new owner in
    + * the pi_state but cannot access the user space value.
    + *
    + * [7] pi_state->owner can only be NULL when the OWNER_DIED bit is set.
    + *
    + * [8] Owner and user space value match
    + *
    + * [9] There is no transient state which sets the user space TID to 0
    + * except exit_robust_list(), but this is indicated by the
    + * FUTEX_OWNER_DIED bit. See [4]
    + *
    + * [10] There is no transient state which leaves owner and user space
    + * TID out of sync. Except one error case where the kernel is denied
    + * write access to the user address, see fixup_pi_state_owner().
    + *
    + *
    + * Serialization and lifetime rules:
    + *
    + * hb->lock:
    + *
    + * hb -> futex_q, relation
    + * futex_q -> pi_state, relation
    + *
    + * (cannot be raw because hb can contain arbitrary amount
    + * of futex_q's)
    + *
    + * pi_mutex->wait_lock:
    + *
    + * {uval, pi_state}
    + *
    + * (and pi_mutex 'obviously')
    + *
    + * p->pi_lock:
    + *
    + * p->pi_state_list -> pi_state->list, relation
    + * pi_mutex->owner -> pi_state->owner, relation
    + *
    + * pi_state->refcount:
    + *
    + * pi_state lifetime
    + *
    + *
    + * Lock order:
    + *
    + * hb->lock
    + * pi_mutex->wait_lock
    + * p->pi_lock
    + *
    + */
    +
    +/*
    + * Validate that the existing waiter has a pi_state and sanity check
    + * the pi_state against the user space value. If correct, attach to
    + * it.
    + */
    +static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
    + struct futex_pi_state *pi_state,
    + struct futex_pi_state **ps)
    +{
    + pid_t pid = uval & FUTEX_TID_MASK;
    + u32 uval2;
    + int ret;
    +
    + /*
    + * Userspace might have messed up non-PI and PI futexes [3]
    + */
    + if (unlikely(!pi_state))
    + return -EINVAL;
    +
    + /*
    + * We get here with hb->lock held, and having found a
    + * futex_top_waiter(). This means that futex_lock_pi() of said futex_q
    + * has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
    + * which in turn means that futex_lock_pi() still has a reference on
    + * our pi_state.
    + *
    + * The waiter holding a reference on @pi_state also protects against
    + * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
    + * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
    + * free pi_state before we can take a reference ourselves.
    + */
    + WARN_ON(!refcount_read(&pi_state->refcount));
    +
    + /*
    + * Now that we have a pi_state, we can acquire wait_lock
    + * and do the state validation.
    + */
    + raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    +
    + /*
    + * Since {uval, pi_state} is serialized by wait_lock, and our current
    + * uval was read without holding it, it can have changed. Verify it
    + * still is what we expect it to be, otherwise retry the entire
    + * operation.
    + */
    + if (get_futex_value_locked(&uval2, uaddr))
    + goto out_efault;
    +
    + if (uval != uval2)
    + goto out_eagain;
    +
    + /*
    + * Handle the owner died case:
    + */
    + if (uval & FUTEX_OWNER_DIED) {
    + /*
    + * exit_pi_state_list sets owner to NULL and wakes the
    + * topmost waiter. The task which acquires the
    + * pi_state->rt_mutex will fixup owner.
    + */
    + if (!pi_state->owner) {
    + /*
    + * No pi state owner, but the user space TID
    + * is not 0. Inconsistent state. [5]
    + */
    + if (pid)
    + goto out_einval;
    + /*
    + * Take a ref on the state and return success. [4]
    + */
    + goto out_attach;
    + }
    +
    + /*
    + * If TID is 0, then either the dying owner has not
    + * yet executed exit_pi_state_list() or some waiter
    + * acquired the rtmutex in the pi state, but did not
    + * yet fixup the TID in user space.
    + *
    + * Take a ref on the state and return success. [6]
    + */
    + if (!pid)
    + goto out_attach;
    + } else {
    + /*
    + * If the owner died bit is not set, then the pi_state
    + * must have an owner. [7]
    + */
    + if (!pi_state->owner)
    + goto out_einval;
    + }
    +
    + /*
    + * Bail out if user space manipulated the futex value. If pi
    + * state exists then the owner TID must be the same as the
    + * user space TID. [9/10]
    + */
    + if (pid != task_pid_vnr(pi_state->owner))
    + goto out_einval;
    +
    +out_attach:
    + get_pi_state(pi_state);
    + raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    + *ps = pi_state;
    + return 0;
    +
    +out_einval:
    + ret = -EINVAL;
    + goto out_error;
    +
    +out_eagain:
    + ret = -EAGAIN;
    + goto out_error;
    +
    +out_efault:
    + ret = -EFAULT;
    + goto out_error;
    +
    +out_error:
    + raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    + return ret;
    +}
    +
    +/**
    + * wait_for_owner_exiting - Block until the owner has exited
    + * @ret: owner's current futex lock status
    + * @exiting: Pointer to the exiting task
    + *
    + * Caller must hold a refcount on @exiting.
    + */
    +static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
    +{
    + if (ret != -EBUSY) {
    + WARN_ON_ONCE(exiting);
    + return;
    + }
    +
    + if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
    + return;
    +
    + mutex_lock(&exiting->futex_exit_mutex);
    + /*
    + * No point in doing state checking here. If the waiter got here
    + * while the task was in exec()->exec_futex_release() then it can
    + * have any FUTEX_STATE_* value when the waiter has acquired the
    + * mutex. OK, if running, EXITING or DEAD if it reached exit()
    + * already. Highly unlikely and not a problem. Just one more round
    + * through the futex maze.
    + */
    + mutex_unlock(&exiting->futex_exit_mutex);
    +
    + put_task_struct(exiting);
    +}
    +
    +static int handle_exit_race(u32 __user *uaddr, u32 uval,
    + struct task_struct *tsk)
    +{
    + u32 uval2;
    +
    + /*
    + * If the futex exit state is not yet FUTEX_STATE_DEAD, tell the
    + * caller that the alleged owner is busy.
    + */
    + if (tsk && tsk->futex_state != FUTEX_STATE_DEAD)
    + return -EBUSY;
    +
    + /*
    + * Reread the user space value to handle the following situation:
    + *
    + * CPU0 CPU1
    + *
    + * sys_exit() sys_futex()
    + * do_exit() futex_lock_pi()
    + * futex_lock_pi_atomic()
    + * exit_signals(tsk) No waiters:
    + * tsk->flags |= PF_EXITING; *uaddr == 0x00000PID
    + * mm_release(tsk) Set waiter bit
    + * exit_robust_list(tsk) { *uaddr = 0x80000PID;
    + * Set owner died attach_to_pi_owner() {
    + * *uaddr = 0xC0000000; tsk = get_task(PID);
    + * } if (!tsk->flags & PF_EXITING) {
    + * ... attach();
    + * tsk->futex_state = } else {
    + * FUTEX_STATE_DEAD; if (tsk->futex_state !=
    + * FUTEX_STATE_DEAD)
    + * return -EAGAIN;
    + * return -ESRCH; <--- FAIL
    + * }
    + *
    + * Returning ESRCH unconditionally is wrong here because the
    + * user space value has been changed by the exiting task.
    + *
    + * The same logic applies to the case where the exiting task is
    + * already gone.
    + */
    + if (get_futex_value_locked(&uval2, uaddr))
    + return -EFAULT;
    +
    + /* If the user space value has changed, try again. */
    + if (uval2 != uval)
    + return -EAGAIN;
    +
    + /*
    + * The exiting task did not have a robust list, the robust list was
    + * corrupted or the user space value in *uaddr is simply bogus.
    + * Give up and tell user space.
    + */
    + return -ESRCH;
    +}
    +
    +static void __attach_to_pi_owner(struct task_struct *p, union futex_key *key,
    + struct futex_pi_state **ps)
    +{
    + /*
    + * No existing pi state. First waiter. [2]
    + *
    + * This creates pi_state, we have hb->lock held, this means nothing can
    + * observe this state, wait_lock is irrelevant.
    + */
    + struct futex_pi_state *pi_state = alloc_pi_state();
    +
    + /*
    + * Initialize the pi_mutex in locked state and make @p
    + * the owner of it:
    + */
    + rt_mutex_init_proxy_locked(&pi_state->pi_mutex, p);
    +
    + /* Store the key for possible exit cleanups: */
    + pi_state->key = *key;
    +
    + WARN_ON(!list_empty(&pi_state->list));
    + list_add(&pi_state->list, &p->pi_state_list);
    + /*
    + * Assignment without holding pi_state->pi_mutex.wait_lock is safe
    + * because there is no concurrency as the object is not published yet.
    + */
    + pi_state->owner = p;
    +
    + *ps = pi_state;
    +}
    +/*
    + * Lookup the task for the TID provided from user space and attach to
    + * it after doing proper sanity checks.
    + */
    +static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
    + struct futex_pi_state **ps,
    + struct task_struct **exiting)
    +{
    + pid_t pid = uval & FUTEX_TID_MASK;
    + struct task_struct *p;
    +
    + /*
    + * We are the first waiter - try to look up the real owner and attach
    + * the new pi_state to it, but bail out when TID = 0 [1]
    + *
    + * The !pid check is paranoid. None of the call sites should end up
    + * with pid == 0, but better safe than sorry. Let the caller retry
    + */
    + if (!pid)
    + return -EAGAIN;
    + p = find_get_task_by_vpid(pid);
    + if (!p)
    + return handle_exit_race(uaddr, uval, NULL);
    +
    + if (unlikely(p->flags & PF_KTHREAD)) {
    + put_task_struct(p);
    + return -EPERM;
    + }
    +
    + /*
    + * We need to look at the task state to figure out, whether the
    + * task is exiting. To protect against the change of the task state
    + * in futex_exit_release(), we do this protected by p->pi_lock:
    + */
    + raw_spin_lock_irq(&p->pi_lock);
    + if (unlikely(p->futex_state != FUTEX_STATE_OK)) {
    + /*
    + * The task is on the way out. When the futex state is
    + * FUTEX_STATE_DEAD, we know that the task has finished
    + * the cleanup:
    + */
    + int ret = handle_exit_race(uaddr, uval, p);
    +
    + raw_spin_unlock_irq(&p->pi_lock);
    + /*
    + * If the owner task is between FUTEX_STATE_EXITING and
    + * FUTEX_STATE_DEAD then store the task pointer and keep
    + * the reference on the task struct. The calling code will
    + * drop all locks, wait for the task to reach
    + * FUTEX_STATE_DEAD and then drop the refcount. This is
    + * required to prevent a live lock when the current task
    + * preempted the exiting task between the two states.
    + */
    + if (ret == -EBUSY)
    + *exiting = p;
    + else
    + put_task_struct(p);
    + return ret;
    + }
    +
    + __attach_to_pi_owner(p, key, ps);
    + raw_spin_unlock_irq(&p->pi_lock);
    +
    + put_task_struct(p);
    +
    + return 0;
    +}
    +
    +static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
    +{
    + int err;
    + u32 curval;
    +
    + if (unlikely(should_fail_futex(true)))
    + return -EFAULT;
    +
    + err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
    + if (unlikely(err))
    + return err;
    +
    + /* If user space value changed, let the caller retry */
    + return curval != uval ? -EAGAIN : 0;
    +}
    +
    +/**
    + * futex_lock_pi_atomic() - Atomic work required to acquire a pi aware futex
    + * @uaddr: the pi futex user address
    + * @hb: the pi futex hash bucket
    + * @key: the futex key associated with uaddr and hb
    + * @ps: the pi_state pointer where we store the result of the
    + * lookup
    + * @task: the task to perform the atomic lock work for. This will
    + * be "current" except in the case of requeue pi.
    + * @exiting: Pointer to store the task pointer of the owner task
    + * which is in the middle of exiting
    + * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
    + *
    + * Return:
    + * - 0 - ready to wait;
    + * - 1 - acquired the lock;
    + * - <0 - error
    + *
    + * The hb->lock must be held by the caller.
    + *
    + * @exiting is only set when the return value is -EBUSY. If so, this holds
    + * a refcount on the exiting task on return and the caller needs to drop it
    + * after waiting for the exit to complete.
    + */
    +static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
    + union futex_key *key,
    + struct futex_pi_state **ps,
    + struct task_struct *task,
    + struct task_struct **exiting,
    + int set_waiters)
    +{
    + u32 uval, newval, vpid = task_pid_vnr(task);
    + struct futex_q *top_waiter;
    + int ret;
    +
    + /*
    + * Read the user space value first so we can validate a few
    + * things before proceeding further.
    + */
    + if (get_futex_value_locked(&uval, uaddr))
    + return -EFAULT;
    +
    + if (unlikely(should_fail_futex(true)))
    + return -EFAULT;
    +
    + /*
    + * Detect deadlocks.
    + */
    + if ((unlikely((uval & FUTEX_TID_MASK) == vpid)))
    + return -EDEADLK;
    +
    + if ((unlikely(should_fail_futex(true))))
    + return -EDEADLK;
    +
    + /*
    + * Lookup existing state first. If it exists, try to attach to
    + * its pi_state.
    + */
    + top_waiter = futex_top_waiter(hb, key);
    + if (top_waiter)
    + return attach_to_pi_state(uaddr, uval, top_waiter->pi_state, ps);
    +
    + /*
    + * No waiter and user TID is 0. We are here because the
    + * waiters or the owner died bit is set or called from
    + * requeue_cmp_pi or for whatever reason something took the
    + * syscall.
    + */
    + if (!(uval & FUTEX_TID_MASK)) {
    + /*
    + * We take over the futex. No other waiters and the user space
    + * TID is 0. We preserve the owner died bit.
    + */
    + newval = uval & FUTEX_OWNER_DIED;
    + newval |= vpid;
    +
    + /* The futex requeue_pi code can enforce the waiters bit */
    + if (set_waiters)
    + newval |= FUTEX_WAITERS;
    +
    + ret = lock_pi_update_atomic(uaddr, uval, newval);
    + if (ret)
    + return ret;
    +
    + /*
    + * If the waiter bit was requested the caller also needs PI
    + * state attached to the new owner of the user space futex.
    + *
    + * @task is guaranteed to be alive and it cannot be exiting
    + * because it is either sleeping or waiting in
    + * futex_requeue_pi_wakeup_sync().
    + *
    + * No need to do the full attach_to_pi_owner() exercise
    + * because @task is known and valid.
    + */
    + if (set_waiters) {
    + raw_spin_lock_irq(&task->pi_lock);
    + __attach_to_pi_owner(task, key, ps);
    + raw_spin_unlock_irq(&task->pi_lock);
    + }
    + return 1;
    + }
    +
    + /*
    + * First waiter. Set the waiters bit before attaching ourself to
    + * the owner. If owner tries to unlock, it will be forced into
    + * the kernel and blocked on hb->lock.
    + */
    + newval = uval | FUTEX_WAITERS;
    + ret = lock_pi_update_atomic(uaddr, uval, newval);
    + if (ret)
    + return ret;
    + /*
    + * If the update of the user space value succeeded, we try to
    + * attach to the owner. If that fails, no harm done, we only
    + * set the FUTEX_WAITERS bit in the user space variable.
    + */
    + return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
    +}
    +
    +/**
    + * __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
    + * @q: The futex_q to unqueue
    + *
    + * The q->lock_ptr must not be NULL and must be held by the caller.
    + */
    +static void __unqueue_futex(struct futex_q *q)
    +{
    + struct futex_hash_bucket *hb;
    +
    + if (WARN_ON_SMP(!q->lock_ptr) || WARN_ON(plist_node_empty(&q->list)))
    + return;
    + lockdep_assert_held(q->lock_ptr);
    +
    + hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
    + plist_del(&q->list, &hb->chain);
    + hb_waiters_dec(hb);
    +}
    +
    +/*
    + * The hash bucket lock must be held when this is called.
    + * Afterwards, the futex_q must not be accessed. Callers
    + * must ensure to later call wake_up_q() for the actual
    + * wakeups to occur.
    + */
    +static void mark_wake_futex(struct wake_q_head *wake_q, struct futex_q *q)
    +{
    + struct task_struct *p = q->task;
    +
    + if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
    + return;
    +
    + get_task_struct(p);
    + __unqueue_futex(q);
    + /*
    + * The waiting task can free the futex_q as soon as q->lock_ptr = NULL
    + * is written, without taking any locks. This is possible in the event
    + * of a spurious wakeup, for example. A memory barrier is required here
    + * to prevent the following store to lock_ptr from getting ahead of the
    + * plist_del in __unqueue_futex().
    + */
    + smp_store_release(&q->lock_ptr, NULL);
    +
    + /*
    + * Queue the task for later wakeup for after we've released
    + * the hb->lock.
    + */
    + wake_q_add_safe(wake_q, p);
    +}
    +
    +/*
    + * Caller must hold a reference on @pi_state.
    + */
    +static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
    +{
    + struct rt_mutex_waiter *top_waiter;
    + struct task_struct *new_owner;
    + bool postunlock = false;
    + DEFINE_RT_WAKE_Q(wqh);
    + u32 curval, newval;
    + int ret = 0;
    +
    + top_waiter = rt_mutex_top_waiter(&pi_state->pi_mutex);
    + if (WARN_ON_ONCE(!top_waiter)) {
    + /*
    + * As per the comment in futex_unlock_pi() this should not happen.
    + *
    + * When this happens, give up our locks and try again, giving
    + * the futex_lock_pi() instance time to complete, either by
    + * waiting on the rtmutex or removing itself from the futex
    + * queue.
    + */
    + ret = -EAGAIN;
    + goto out_unlock;
    + }
    +
    + new_owner = top_waiter->task;
    +
    + /*
    + * We pass it to the next owner. The WAITERS bit is always kept
    + * enabled while there is PI state around. We cleanup the owner
    + * died bit, because we are the owner.
    + */
    + newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
    +
    + if (unlikely(should_fail_futex(true))) {
    + ret = -EFAULT;
    + goto out_unlock;
    + }
    +
    + ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
    + if (!ret && (curval != uval)) {
    + /*
    + * If a unconditional UNLOCK_PI operation (user space did not
    + * try the TID->0 transition) raced with a waiter setting the
    + * FUTEX_WAITERS flag between get_user() and locking the hash
    + * bucket lock, retry the operation.
    + */
    + if ((FUTEX_TID_MASK & curval) == uval)
    + ret = -EAGAIN;
    + else
    + ret = -EINVAL;
    + }
    +
    + if (!ret) {
    + /*
    + * This is a point of no return; once we modified the uval
    + * there is no going back and subsequent operations must
    + * not fail.
    + */
    + pi_state_update_owner(pi_state, new_owner);
    + postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wqh);
    + }
    +
    +out_unlock:
    + raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    +
    + if (postunlock)
    + rt_mutex_postunlock(&wqh);
    +
    + return ret;
    +}
    +
    +/*
    + * Express the locking dependencies for lockdep:
    + */
    +static inline void
    +double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
    +{
    + if (hb1 <= hb2) {
    + spin_lock(&hb1->lock);
    + if (hb1 < hb2)
    + spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
    + } else { /* hb1 > hb2 */
    + spin_lock(&hb2->lock);
    + spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
    + }
    +}
    +
    +static inline void
    +double_unlock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
    +{
    + spin_unlock(&hb1->lock);
    + if (hb1 != hb2)
    + spin_unlock(&hb2->lock);
    +}
    +
    +/*
    + * Wake up waiters matching bitset queued on this futex (uaddr).
    + */
    +static int
    +futex_wake(u32 __user *uaddr, unsigned int flags, int nr_wake, u32 bitset)
    +{
    + struct futex_hash_bucket *hb;
    + struct futex_q *this, *next;
    + union futex_key key = FUTEX_KEY_INIT;
    + int ret;
    + DEFINE_WAKE_Q(wake_q);
    +
    + if (!bitset)
    + return -EINVAL;
    +
    + ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_READ);
    + if (unlikely(ret != 0))
    + return ret;
    +
    + hb = hash_futex(&key);
    +
    + /* Make sure we really have tasks to wakeup */
    + if (!hb_waiters_pending(hb))
    + return ret;
    +
    + spin_lock(&hb->lock);
    +
    + plist_for_each_entry_safe(this, next, &hb->chain, list) {
    + if (match_futex (&this->key, &key)) {
    + if (this->pi_state || this->rt_waiter) {
    + ret = -EINVAL;
    + break;
    + }
    +
    + /* Check if one of the bits is set in both bitsets */
    + if (!(this->bitset & bitset))
    + continue;
    +
    + mark_wake_futex(&wake_q, this);
    + if (++ret >= nr_wake)
    + break;
    + }
    + }
    +
    + spin_unlock(&hb->lock);
    + wake_up_q(&wake_q);
    + return ret;
    +}
    +
    +static int futex_atomic_op_inuser(unsigned int encoded_op, u32 __user *uaddr)
    +{
    + unsigned int op = (encoded_op & 0x70000000) >> 28;
    + unsigned int cmp = (encoded_op & 0x0f000000) >> 24;
    + int oparg = sign_extend32((encoded_op & 0x00fff000) >> 12, 11);
    + int cmparg = sign_extend32(encoded_op & 0x00000fff, 11);
    + int oldval, ret;
    +
    + if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28)) {
    + if (oparg < 0 || oparg > 31) {
    + char comm[sizeof(current->comm)];
    + /*
    + * kill this print and return -EINVAL when userspace
    + * is sane again
    + */
    + pr_info_ratelimited("futex_wake_op: %s tries to shift op by %d; fix this program\n",
    + get_task_comm(comm, current), oparg);
    + oparg &= 31;
    + }
    + oparg = 1 << oparg;
    + }
    +
    + pagefault_disable();
    + ret = arch_futex_atomic_op_inuser(op, oparg, &oldval, uaddr);
    + pagefault_enable();
    + if (ret)
    + return ret;
    +
    + switch (cmp) {
    + case FUTEX_OP_CMP_EQ:
    + return oldval == cmparg;
    + case FUTEX_OP_CMP_NE:
    + return oldval != cmparg;
    + case FUTEX_OP_CMP_LT:
    + return oldval < cmparg;
    + case FUTEX_OP_CMP_GE:
    + return oldval >= cmparg;
    + case FUTEX_OP_CMP_LE:
    + return oldval <= cmparg;
    + case FUTEX_OP_CMP_GT:
    + return oldval > cmparg;
    + default:
    + return -ENOSYS;
    + }
    +}
    +
    +/*
    + * Wake up all waiters hashed on the physical page that is mapped
    + * to this virtual address:
    + */
    +static int
    +futex_wake_op(u32 __user *uaddr1, unsigned int flags, u32 __user *uaddr2,
    + int nr_wake, int nr_wake2, int op)
    +{
    + union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
    + struct futex_hash_bucket *hb1, *hb2;
    + struct futex_q *this, *next;
    + int ret, op_ret;
    + DEFINE_WAKE_Q(wake_q);
    +
    +retry:
    + ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
    + if (unlikely(ret != 0))
    + return ret;
    + ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
    + if (unlikely(ret != 0))
    + return ret;
    +
    + hb1 = hash_futex(&key1);
    + hb2 = hash_futex(&key2);
    +
    +retry_private:
    + double_lock_hb(hb1, hb2);
    + op_ret = futex_atomic_op_inuser(op, uaddr2);
    + if (unlikely(op_ret < 0)) {
    + double_unlock_hb(hb1, hb2);
    +
    + if (!IS_ENABLED(CONFIG_MMU) ||
    + unlikely(op_ret != -EFAULT && op_ret != -EAGAIN)) {
    + /*
    + * we don't get EFAULT from MMU faults if we don't have
    + * an MMU, but we might get them from range checking
    + */
    + ret = op_ret;
    + return ret;
    + }
    +
    + if (op_ret == -EFAULT) {
    + ret = fault_in_user_writeable(uaddr2);
    + if (ret)
    + return ret;
    + }
    +
    + cond_resched();
    + if (!(flags & FLAGS_SHARED))
    + goto retry_private;
    + goto retry;
    + }
    +
    + plist_for_each_entry_safe(this, next, &hb1->chain, list) {
    + if (match_futex (&this->key, &key1)) {
    + if (this->pi_state || this->rt_waiter) {
    + ret = -EINVAL;
    + goto out_unlock;
    + }
    + mark_wake_futex(&wake_q, this);
    + if (++ret >= nr_wake)
    + break;
    + }
    + }
    +
    + if (op_ret > 0) {
    + op_ret = 0;
    + plist_for_each_entry_safe(this, next, &hb2->chain, list) {
    + if (match_futex (&this->key, &key2)) {
    + if (this->pi_state || this->rt_waiter) {
    + ret = -EINVAL;
    + goto out_unlock;
    + }
    + mark_wake_futex(&wake_q, this);
    + if (++op_ret >= nr_wake2)
    + break;
    + }
    + }
    + ret += op_ret;
    + }
    +
    +out_unlock:
    + double_unlock_hb(hb1, hb2);
    + wake_up_q(&wake_q);
    + return ret;
    +}
    +
    +/**
    + * requeue_futex() - Requeue a futex_q from one hb to another
    + * @q: the futex_q to requeue
    + * @hb1: the source hash_bucket
    + * @hb2: the target hash_bucket
    + * @key2: the new key for the requeued futex_q
    + */
    +static inline
    +void requeue_futex(struct futex_q *q, struct futex_hash_bucket *hb1,
    + struct futex_hash_bucket *hb2, union futex_key *key2)
    +{
    +
    + /*
    + * If key1 and key2 hash to the same bucket, no need to
    + * requeue.
    + */
    + if (likely(&hb1->chain != &hb2->chain)) {
    + plist_del(&q->list, &hb1->chain);
    + hb_waiters_dec(hb1);
    + hb_waiters_inc(hb2);
    + plist_add(&q->list, &hb2->chain);
    + q->lock_ptr = &hb2->lock;
    + }
    + q->key = *key2;
    +}
    +
    +static inline bool futex_requeue_pi_prepare(struct futex_q *q,
    + struct futex_pi_state *pi_state)
    +{
    + int old, new;
    +
    + /*
    + * Set state to Q_REQUEUE_PI_IN_PROGRESS unless an early wakeup has
    + * already set Q_REQUEUE_PI_IGNORE to signal that requeue should
    + * ignore the waiter.
    + */
    + old = atomic_read_acquire(&q->requeue_state);
    + do {
    + if (old == Q_REQUEUE_PI_IGNORE)
    + return false;
    +
    + /*
    + * futex_proxy_trylock_atomic() might have set it to
    + * IN_PROGRESS and a interleaved early wake to WAIT.
    + *
    + * It was considered to have an extra state for that
    + * trylock, but that would just add more conditionals
    + * all over the place for a dubious value.
    + */
    + if (old != Q_REQUEUE_PI_NONE)
    + break;
    +
    + new = Q_REQUEUE_PI_IN_PROGRESS;
    + } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
    +
    + q->pi_state = pi_state;
    + return true;
    +}
    +
    +static inline void futex_requeue_pi_complete(struct futex_q *q, int locked)
    +{
    + int old, new;
    +
    + old = atomic_read_acquire(&q->requeue_state);
    + do {
    + if (old == Q_REQUEUE_PI_IGNORE)
    + return;
    +
    + if (locked >= 0) {
    + /* Requeue succeeded. Set DONE or LOCKED */
    + WARN_ON_ONCE(old != Q_REQUEUE_PI_IN_PROGRESS &&
    + old != Q_REQUEUE_PI_WAIT);
    + new = Q_REQUEUE_PI_DONE + locked;
    + } else if (old == Q_REQUEUE_PI_IN_PROGRESS) {
    + /* Deadlock, no early wakeup interleave */
    + new = Q_REQUEUE_PI_NONE;
    + } else {
    + /* Deadlock, early wakeup interleave. */
    + WARN_ON_ONCE(old != Q_REQUEUE_PI_WAIT);
    + new = Q_REQUEUE_PI_IGNORE;
    + }
    + } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
    +
    +#ifdef CONFIG_PREEMPT_RT
    + /* If the waiter interleaved with the requeue let it know */
    + if (unlikely(old == Q_REQUEUE_PI_WAIT))
    + rcuwait_wake_up(&q->requeue_wait);
    +#endif
    +}
    +
    +static inline int futex_requeue_pi_wakeup_sync(struct futex_q *q)
    +{
    + int old, new;
    +
    + old = atomic_read_acquire(&q->requeue_state);
    + do {
    + /* Is requeue done already? */
    + if (old >= Q_REQUEUE_PI_DONE)
    + return old;
    +
    + /*
    + * If not done, then tell the requeue code to either ignore
    + * the waiter or to wake it up once the requeue is done.
    + */
    + new = Q_REQUEUE_PI_WAIT;
    + if (old == Q_REQUEUE_PI_NONE)
    + new = Q_REQUEUE_PI_IGNORE;
    + } while (!atomic_try_cmpxchg(&q->requeue_state, &old, new));
    +
    + /* If the requeue was in progress, wait for it to complete */
    + if (old == Q_REQUEUE_PI_IN_PROGRESS) {
    +#ifdef CONFIG_PREEMPT_RT
    + rcuwait_wait_event(&q->requeue_wait,
    + atomic_read(&q->requeue_state) != Q_REQUEUE_PI_WAIT,
    + TASK_UNINTERRUPTIBLE);
    +#else
    + (void)atomic_cond_read_relaxed(&q->requeue_state, VAL != Q_REQUEUE_PI_WAIT);
    +#endif
    + }
    +
    + /*
    + * Requeue is now either prohibited or complete. Reread state
    + * because during the wait above it might have changed. Nothing
    + * will modify q->requeue_state after this point.
    + */
    + return atomic_read(&q->requeue_state);
    +}
    +
    +/**
    + * requeue_pi_wake_futex() - Wake a task that acquired the lock during requeue
    + * @q: the futex_q
    + * @key: the key of the requeue target futex
    + * @hb: the hash_bucket of the requeue target futex
    + *
    + * During futex_requeue, with requeue_pi=1, it is possible to acquire the
    + * target futex if it is uncontended or via a lock steal.
    + *
    + * 1) Set @q::key to the requeue target futex key so the waiter can detect
    + * the wakeup on the right futex.
    + *
    + * 2) Dequeue @q from the hash bucket.
    + *
    + * 3) Set @q::rt_waiter to NULL so the woken up task can detect atomic lock
    + * acquisition.
    + *
    + * 4) Set the q->lock_ptr to the requeue target hb->lock for the case that
    + * the waiter has to fixup the pi state.
    + *
    + * 5) Complete the requeue state so the waiter can make progress. After
    + * this point the waiter task can return from the syscall immediately in
    + * case that the pi state does not have to be fixed up.
    + *
    + * 6) Wake the waiter task.
    + *
    + * Must be called with both q->lock_ptr and hb->lock held.
    + */
    +static inline
    +void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
    + struct futex_hash_bucket *hb)
    +{
    + q->key = *key;
    +
    + __unqueue_futex(q);
    +
    + WARN_ON(!q->rt_waiter);
    + q->rt_waiter = NULL;
    +
    + q->lock_ptr = &hb->lock;
    +
    + /* Signal locked state to the waiter */
    + futex_requeue_pi_complete(q, 1);
    + wake_up_state(q->task, TASK_NORMAL);
    +}
    +
    +/**
    + * futex_proxy_trylock_atomic() - Attempt an atomic lock for the top waiter
    + * @pifutex: the user address of the to futex
    + * @hb1: the from futex hash bucket, must be locked by the caller
    + * @hb2: the to futex hash bucket, must be locked by the caller
    + * @key1: the from futex key
    + * @key2: the to futex key
    + * @ps: address to store the pi_state pointer
    + * @exiting: Pointer to store the task pointer of the owner task
    + * which is in the middle of exiting
    + * @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
    + *
    + * Try and get the lock on behalf of the top waiter if we can do it atomically.
    + * Wake the top waiter if we succeed. If the caller specified set_waiters,
    + * then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
    + * hb1 and hb2 must be held by the caller.
    + *
    + * @exiting is only set when the return value is -EBUSY. If so, this holds
    + * a refcount on the exiting task on return and the caller needs to drop it
    + * after waiting for the exit to complete.
    + *
    + * Return:
    + * - 0 - failed to acquire the lock atomically;
    + * - >0 - acquired the lock, return value is vpid of the top_waiter
    + * - <0 - error
    + */
    +static int
    +futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
    + struct futex_hash_bucket *hb2, union futex_key *key1,
    + union futex_key *key2, struct futex_pi_state **ps,
    + struct task_struct **exiting, int set_waiters)
    +{
    + struct futex_q *top_waiter = NULL;
    + u32 curval;
    + int ret;
    +
    + if (get_futex_value_locked(&curval, pifutex))
    + return -EFAULT;
    +
    + if (unlikely(should_fail_futex(true)))
    + return -EFAULT;
    +
    + /*
    + * Find the top_waiter and determine if there are additional waiters.
    + * If the caller intends to requeue more than 1 waiter to pifutex,
    + * force futex_lock_pi_atomic() to set the FUTEX_WAITERS bit now,
    + * as we have means to handle the possible fault. If not, don't set
    + * the bit unnecessarily as it will force the subsequent unlock to enter
    + * the kernel.
    + */
    + top_waiter = futex_top_waiter(hb1, key1);
    +
    + /* There are no waiters, nothing for us to do. */
    + if (!top_waiter)
    + return 0;
    +
    + /*
    + * Ensure that this is a waiter sitting in futex_wait_requeue_pi()
    + * and waiting on the 'waitqueue' futex which is always !PI.
    + */
    + if (!top_waiter->rt_waiter || top_waiter->pi_state)
    + return -EINVAL;
    +
    + /* Ensure we requeue to the expected futex. */
    + if (!match_futex(top_waiter->requeue_pi_key, key2))
    + return -EINVAL;
    +
    + /* Ensure that this does not race against an early wakeup */
    + if (!futex_requeue_pi_prepare(top_waiter, NULL))
    + return -EAGAIN;
    +
    + /*
    + * Try to take the lock for top_waiter and set the FUTEX_WAITERS bit
    + * in the contended case or if @set_waiters is true.
    + *
    + * In the contended case PI state is attached to the lock owner. If
    + * the user space lock can be acquired then PI state is attached to
    + * the new owner (@top_waiter->task) when @set_waiters is true.
    + */
    + ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
    + exiting, set_waiters);
    + if (ret == 1) {
    + /*
    + * Lock was acquired in user space and PI state was
    + * attached to @top_waiter->task. That means state is fully
    + * consistent and the waiter can return to user space
    + * immediately after the wakeup.
    + */
    + requeue_pi_wake_futex(top_waiter, key2, hb2);
    + } else if (ret < 0) {
    + /* Rewind top_waiter::requeue_state */
    + futex_requeue_pi_complete(top_waiter, ret);
    + } else {
    + /*
    + * futex_lock_pi_atomic() did not acquire the user space
    + * futex, but managed to establish the proxy lock and pi
    + * state. top_waiter::requeue_state cannot be fixed up here
    + * because the waiter is not enqueued on the rtmutex
    + * yet. This is handled at the callsite depending on the
    + * result of rt_mutex_start_proxy_lock() which is
    + * guaranteed to be reached with this function returning 0.
    + */
    + }
    + return ret;
    +}
    +
    +/**
    + * futex_requeue() - Requeue waiters from uaddr1 to uaddr2
    + * @uaddr1: source futex user address
    + * @flags: futex flags (FLAGS_SHARED, etc.)
    + * @uaddr2: target futex user address
    + * @nr_wake: number of waiters to wake (must be 1 for requeue_pi)
    + * @nr_requeue: number of waiters to requeue (0-INT_MAX)
    + * @cmpval: @uaddr1 expected value (or %NULL)
    + * @requeue_pi: if we are attempting to requeue from a non-pi futex to a
    + * pi futex (pi to pi requeue is not supported)
    + *
    + * Requeue waiters on uaddr1 to uaddr2. In the requeue_pi case, try to acquire
    + * uaddr2 atomically on behalf of the top waiter.
    + *
    + * Return:
    + * - >=0 - on success, the number of tasks requeued or woken;
    + * - <0 - on error
    + */
    +static int futex_requeue(u32 __user *uaddr1, unsigned int flags,
    + u32 __user *uaddr2, int nr_wake, int nr_requeue,
    + u32 *cmpval, int requeue_pi)
    +{
    + union futex_key key1 = FUTEX_KEY_INIT, key2 = FUTEX_KEY_INIT;
    + int task_count = 0, ret;
    + struct futex_pi_state *pi_state = NULL;
    + struct futex_hash_bucket *hb1, *hb2;
    + struct futex_q *this, *next;
    + DEFINE_WAKE_Q(wake_q);
    +
    + if (nr_wake < 0 || nr_requeue < 0)
    + return -EINVAL;
    +
    + /*
    + * When PI not supported: return -ENOSYS if requeue_pi is true,
    + * consequently the compiler knows requeue_pi is always false past
    + * this point which will optimize away all the conditional code
    + * further down.
    + */
    + if (!IS_ENABLED(CONFIG_FUTEX_PI) && requeue_pi)
    + return -ENOSYS;
    +
    + if (requeue_pi) {
    + /*
    + * Requeue PI only works on two distinct uaddrs. This
    + * check is only valid for private futexes. See below.
    + */
    + if (uaddr1 == uaddr2)
    + return -EINVAL;
    +
    + /*
    + * futex_requeue() allows the caller to define the number
    + * of waiters to wake up via the @nr_wake argument. With
    + * REQUEUE_PI, waking up more than one waiter is creating
    + * more problems than it solves. Waking up a waiter makes
    + * only sense if the PI futex @uaddr2 is uncontended as
    + * this allows the requeue code to acquire the futex
    + * @uaddr2 before waking the waiter. The waiter can then
    + * return to user space without further action. A secondary
    + * wakeup would just make the futex_wait_requeue_pi()
    + * handling more complex, because that code would have to
    + * look up pi_state and do more or less all the handling
    + * which the requeue code has to do for the to be requeued
    + * waiters. So restrict the number of waiters to wake to
    + * one, and only wake it up when the PI futex is
    + * uncontended. Otherwise requeue it and let the unlock of
    + * the PI futex handle the wakeup.
    + *
    + * All REQUEUE_PI users, e.g. pthread_cond_signal() and
    + * pthread_cond_broadcast() must use nr_wake=1.
    + */
    + if (nr_wake != 1)
    + return -EINVAL;
    +
    + /*
    + * requeue_pi requires a pi_state, try to allocate it now
    + * without any locks in case it fails.
    + */
    + if (refill_pi_state_cache())
    + return -ENOMEM;
    + }
    +
    +retry:
    + ret = get_futex_key(uaddr1, flags & FLAGS_SHARED, &key1, FUTEX_READ);
    + if (unlikely(ret != 0))
    + return ret;
    + ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2,
    + requeue_pi ? FUTEX_WRITE : FUTEX_READ);
    + if (unlikely(ret != 0))
    + return ret;
    +
    + /*
    + * The check above which compares uaddrs is not sufficient for
    + * shared futexes. We need to compare the keys:
    + */
    + if (requeue_pi && match_futex(&key1, &key2))
    + return -EINVAL;
    +
    + hb1 = hash_futex(&key1);
    + hb2 = hash_futex(&key2);
    +
    +retry_private:
    + hb_waiters_inc(hb2);
    + double_lock_hb(hb1, hb2);
    +
    + if (likely(cmpval != NULL)) {
    + u32 curval;
    +
    + ret = get_futex_value_locked(&curval, uaddr1);
    +
    + if (unlikely(ret)) {
    + double_unlock_hb(hb1, hb2);
    + hb_waiters_dec(hb2);
    +
    + ret = get_user(curval, uaddr1);
    + if (ret)
    + return ret;
    +
    + if (!(flags & FLAGS_SHARED))
    + goto retry_private;
    +
    + goto retry;
    + }
    + if (curval != *cmpval) {
    + ret = -EAGAIN;
    + goto out_unlock;
    + }
    + }
    +
    + if (requeue_pi) {
    + struct task_struct *exiting = NULL;
    +
    + /*
    + * Attempt to acquire uaddr2 and wake the top waiter. If we
    + * intend to requeue waiters, force setting the FUTEX_WAITERS
    + * bit. We force this here where we are able to easily handle
    + * faults rather in the requeue loop below.
    + *
    + * Updates topwaiter::requeue_state if a top waiter exists.
    + */
    + ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
    + &key2, &pi_state,
    + &exiting, nr_requeue);
    +
    + /*
    + * At this point the top_waiter has either taken uaddr2 or
    + * is waiting on it. In both cases pi_state has been
    + * established and an initial refcount on it. In case of an
    + * error there's nothing.
    + *
    + * The top waiter's requeue_state is up to date:
    + *
    + * - If the lock was acquired atomically (ret == 1), then
    + * the state is Q_REQUEUE_PI_LOCKED.
    + *
    + * The top waiter has been dequeued and woken up and can
    + * return to user space immediately. The kernel/user
    + * space state is consistent. In case that there must be
    + * more waiters requeued the WAITERS bit in the user
    + * space futex is set so the top waiter task has to go
    + * into the syscall slowpath to unlock the futex. This
    + * will block until this requeue operation has been
    + * completed and the hash bucket locks have been
    + * dropped.
    + *
    + * - If the trylock failed with an error (ret < 0) then
    + * the state is either Q_REQUEUE_PI_NONE, i.e. "nothing
    + * happened", or Q_REQUEUE_PI_IGNORE when there was an
    + * interleaved early wakeup.
    + *
    + * - If the trylock did not succeed (ret == 0) then the
    + * state is either Q_REQUEUE_PI_IN_PROGRESS or
    + * Q_REQUEUE_PI_WAIT if an early wakeup interleaved.
    + * This will be cleaned up in the loop below, which
    + * cannot fail because futex_proxy_trylock_atomic() did
    + * the same sanity checks for requeue_pi as the loop
    + * below does.
    + */
    + switch (ret) {
    + case 0:
    + /* We hold a reference on the pi state. */
    + break;
    +
    + case 1:
    + /*
    + * futex_proxy_trylock_atomic() acquired the user space
    + * futex. Adjust task_count.
    + */
    + task_count++;
    + ret = 0;
    + break;
    +
    + /*
    + * If the above failed, then pi_state is NULL and
    + * waiter::requeue_state is correct.
    + */
    + case -EFAULT:
    + double_unlock_hb(hb1, hb2);
    + hb_waiters_dec(hb2);
    + ret = fault_in_user_writeable(uaddr2);
    + if (!ret)
    + goto retry;
    + return ret;
    + case -EBUSY:
    + case -EAGAIN:
    + /*
    + * Two reasons for this:
    + * - EBUSY: Owner is exiting and we just wait for the
    + * exit to complete.
    + * - EAGAIN: The user space value changed.
    + */
    + double_unlock_hb(hb1, hb2);
    + hb_waiters_dec(hb2);
    + /*
    + * Handle the case where the owner is in the middle of
    + * exiting. Wait for the exit to complete otherwise
    + * this task might loop forever, aka. live lock.
    + */
    + wait_for_owner_exiting(ret, exiting);
    + cond_resched();
    + goto retry;
    + default:
    + goto out_unlock;
    + }
    + }
    +
    + plist_for_each_entry_safe(this, next, &hb1->chain, list) {
    + if (task_count - nr_wake >= nr_requeue)
    + break;
    +
    + if (!match_futex(&this->key, &key1))
    + continue;
    +
    + /*
    + * FUTEX_WAIT_REQUEUE_PI and FUTEX_CMP_REQUEUE_PI should always
    + * be paired with each other and no other futex ops.
    + *
    + * We should never be requeueing a futex_q with a pi_state,
    + * which is awaiting a futex_unlock_pi().
    + */
    + if ((requeue_pi && !this->rt_waiter) ||
    + (!requeue_pi && this->rt_waiter) ||
    + this->pi_state) {
    + ret = -EINVAL;
    + break;
    + }
    +
    + /* Plain futexes just wake or requeue and are done */
    + if (!requeue_pi) {
    + if (++task_count <= nr_wake)
    + mark_wake_futex(&wake_q, this);
    + else
    + requeue_futex(this, hb1, hb2, &key2);
    + continue;
    + }
    +
    + /* Ensure we requeue to the expected futex for requeue_pi. */
    + if (!match_futex(this->requeue_pi_key, &key2)) {
    + ret = -EINVAL;
    + break;
    + }
    +
    + /*
    + * Requeue nr_requeue waiters and possibly one more in the case
    + * of requeue_pi if we couldn't acquire the lock atomically.
    + *
    + * Prepare the waiter to take the rt_mutex. Take a refcount
    + * on the pi_state and store the pointer in the futex_q
    + * object of the waiter.
    + */
    + get_pi_state(pi_state);
    +
    + /* Don't requeue when the waiter is already on the way out. */
    + if (!futex_requeue_pi_prepare(this, pi_state)) {
    + /*
    + * Early woken waiter signaled that it is on the
    + * way out. Drop the pi_state reference and try the
    + * next waiter. @this->pi_state is still NULL.
    + */
    + put_pi_state(pi_state);
    + continue;
    + }
    +
    + ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
    + this->rt_waiter,
    + this->task);
    +
    + if (ret == 1) {
    + /*
    + * We got the lock. We do neither drop the refcount
    + * on pi_state nor clear this->pi_state because the
    + * waiter needs the pi_state for cleaning up the
    + * user space value. It will drop the refcount
    + * after doing so. this::requeue_state is updated
    + * in the wakeup as well.
    + */
    + requeue_pi_wake_futex(this, &key2, hb2);
    + task_count++;
    + } else if (!ret) {
    + /* Waiter is queued, move it to hb2 */
    + requeue_futex(this, hb1, hb2, &key2);
    + futex_requeue_pi_complete(this, 0);
    + task_count++;
    + } else {
    + /*
    + * rt_mutex_start_proxy_lock() detected a potential
    + * deadlock when we tried to queue that waiter.
    + * Drop the pi_state reference which we took above
    + * and remove the pointer to the state from the
    + * waiters futex_q object.
    + */
    + this->pi_state = NULL;
    + put_pi_state(pi_state);
    + futex_requeue_pi_complete(this, ret);
    + /*
    + * We stop queueing more waiters and let user space
    + * deal with the mess.
    + */
    + break;
    + }
    + }
    +
    + /*
    + * We took an extra initial reference to the pi_state in
    + * futex_proxy_trylock_atomic(). We need to drop it here again.
    + */
    + put_pi_state(pi_state);
    +
    +out_unlock:
    + double_unlock_hb(hb1, hb2);
    + wake_up_q(&wake_q);
    + hb_waiters_dec(hb2);
    + return ret ? ret : task_count;
    +}
    +
    +/* The key must be already stored in q->key. */
    +static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
    + __acquires(&hb->lock)
    +{
    + struct futex_hash_bucket *hb;
    +
    + hb = hash_futex(&q->key);
    +
    + /*
    + * Increment the counter before taking the lock so that
    + * a potential waker won't miss a to-be-slept task that is
    + * waiting for the spinlock. This is safe as all queue_lock()
    + * users end up calling queue_me(). Similarly, for housekeeping,
    + * decrement the counter at queue_unlock() when some error has
    + * occurred and we don't end up adding the task to the list.
    + */
    + hb_waiters_inc(hb); /* implies smp_mb(); (A) */
    +
    + q->lock_ptr = &hb->lock;
    +
    + spin_lock(&hb->lock);
    + return hb;
    +}
    +
    +static inline void
    +queue_unlock(struct futex_hash_bucket *hb)
    + __releases(&hb->lock)
    +{
    + spin_unlock(&hb->lock);
    + hb_waiters_dec(hb);
    +}
    +
    +static inline void __queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
    +{
    + int prio;
    +
    + /*
    + * The priority used to register this element is
    + * - either the real thread-priority for the real-time threads
    + * (i.e. threads with a priority lower than MAX_RT_PRIO)
    + * - or MAX_RT_PRIO for non-RT threads.
    + * Thus, all RT-threads are woken first in priority order, and
    + * the others are woken last, in FIFO order.
    + */
    + prio = min(current->normal_prio, MAX_RT_PRIO);
    +
    + plist_node_init(&q->list, prio);
    + plist_add(&q->list, &hb->chain);
    + q->task = current;
    +}
    +
    +/**
    + * queue_me() - Enqueue the futex_q on the futex_hash_bucket
    + * @q: The futex_q to enqueue
    + * @hb: The destination hash bucket
    + *
    + * The hb->lock must be held by the caller, and is released here. A call to
    + * queue_me() is typically paired with exactly one call to unqueue_me(). The
    + * exceptions involve the PI related operations, which may use unqueue_me_pi()
    + * or nothing if the unqueue is done as part of the wake process and the unqueue
    + * state is implicit in the state of woken task (see futex_wait_requeue_pi() for
    + * an example).
    + */
    +static inline void queue_me(struct futex_q *q, struct futex_hash_bucket *hb)
    + __releases(&hb->lock)
    +{
    + __queue_me(q, hb);
    + spin_unlock(&hb->lock);
    +}
    +
    +/**
    + * unqueue_me() - Remove the futex_q from its futex_hash_bucket
    + * @q: The futex_q to unqueue
    + *
    + * The q->lock_ptr must not be held by the caller. A call to unqueue_me() must
    + * be paired with exactly one earlier call to queue_me().
    + *
    + * Return:
    + * - 1 - if the futex_q was still queued (and we removed unqueued it);
    + * - 0 - if the futex_q was already removed by the waking thread
    + */
    +static int unqueue_me(struct futex_q *q)
    +{
    + spinlock_t *lock_ptr;
    + int ret = 0;
    +
    + /* In the common case we don't take the spinlock, which is nice. */
    +retry:
    + /*
    + * q->lock_ptr can change between this read and the following spin_lock.
    + * Use READ_ONCE to forbid the compiler from reloading q->lock_ptr and
    + * optimizing lock_ptr out of the logic below.
    + */
    + lock_ptr = READ_ONCE(q->lock_ptr);
    + if (lock_ptr != NULL) {
    + spin_lock(lock_ptr);
    + /*
    + * q->lock_ptr can change between reading it and
    + * spin_lock(), causing us to take the wrong lock. This
    + * corrects the race condition.
    + *
    + * Reasoning goes like this: if we have the wrong lock,
    + * q->lock_ptr must have changed (maybe several times)
    + * between reading it and the spin_lock(). It can
    + * change again after the spin_lock() but only if it was
    + * already changed before the spin_lock(). It cannot,
    + * however, change back to the original value. Therefore
    + * we can detect whether we acquired the correct lock.
    + */
    + if (unlikely(lock_ptr != q->lock_ptr)) {
    + spin_unlock(lock_ptr);
    + goto retry;
    + }
    + __unqueue_futex(q);
    +
    + BUG_ON(q->pi_state);
    +
    + spin_unlock(lock_ptr);
    + ret = 1;
    + }
    +
    + return ret;
    +}
    +
    +/*
    + * PI futexes can not be requeued and must remove themselves from the
    + * hash bucket. The hash bucket lock (i.e. lock_ptr) is held.
    + */
    +static void unqueue_me_pi(struct futex_q *q)
    +{
    + __unqueue_futex(q);
    +
    + BUG_ON(!q->pi_state);
    + put_pi_state(q->pi_state);
    + q->pi_state = NULL;
    +}
    +
    +static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
    + struct task_struct *argowner)
    +{
    + struct futex_pi_state *pi_state = q->pi_state;
    + struct task_struct *oldowner, *newowner;
    + u32 uval, curval, newval, newtid;
    + int err = 0;
    +
    + oldowner = pi_state->owner;
    +
    + /*
    + * We are here because either:
    + *
    + * - we stole the lock and pi_state->owner needs updating to reflect
    + * that (@argowner == current),
    + *
    + * or:
    + *
    + * - someone stole our lock and we need to fix things to point to the
    + * new owner (@argowner == NULL).
    + *
    + * Either way, we have to replace the TID in the user space variable.
    + * This must be atomic as we have to preserve the owner died bit here.
    + *
    + * Note: We write the user space value _before_ changing the pi_state
    + * because we can fault here. Imagine swapped out pages or a fork
    + * that marked all the anonymous memory readonly for cow.
    + *
    + * Modifying pi_state _before_ the user space value would leave the
    + * pi_state in an inconsistent state when we fault here, because we
    + * need to drop the locks to handle the fault. This might be observed
    + * in the PID checks when attaching to PI state .
    + */
    +retry:
    + if (!argowner) {
    + if (oldowner != current) {
    + /*
    + * We raced against a concurrent self; things are
    + * already fixed up. Nothing to do.
    + */
    + return 0;
    + }
    +
    + if (__rt_mutex_futex_trylock(&pi_state->pi_mutex)) {
    + /* We got the lock. pi_state is correct. Tell caller. */
    + return 1;
    + }
    +
    + /*
    + * The trylock just failed, so either there is an owner or
    + * there is a higher priority waiter than this one.
    + */
    + newowner = rt_mutex_owner(&pi_state->pi_mutex);
    + /*
    + * If the higher priority waiter has not yet taken over the
    + * rtmutex then newowner is NULL. We can't return here with
    + * that state because it's inconsistent vs. the user space
    + * state. So drop the locks and try again. It's a valid
    + * situation and not any different from the other retry
    + * conditions.
    + */
    + if (unlikely(!newowner)) {
    + err = -EAGAIN;
    + goto handle_err;
    + }
    + } else {
    + WARN_ON_ONCE(argowner != current);
    + if (oldowner == current) {
    + /*
    + * We raced against a concurrent self; things are
    + * already fixed up. Nothing to do.
    + */
    + return 1;
    + }
    + newowner = argowner;
    + }
    +
    + newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
    + /* Owner died? */
    + if (!pi_state->owner)
    + newtid |= FUTEX_OWNER_DIED;
    +
    + err = get_futex_value_locked(&uval, uaddr);
    + if (err)
    + goto handle_err;
    +
    + for (;;) {
    + newval = (uval & FUTEX_OWNER_DIED) | newtid;
    +
    + err = cmpxchg_futex_value_locked(&curval, uaddr, uval, newval);
    + if (err)
    + goto handle_err;
    +
    + if (curval == uval)
    + break;
    + uval = curval;
    + }
    +
    + /*
    + * We fixed up user space. Now we need to fix the pi_state
    + * itself.
    + */
    + pi_state_update_owner(pi_state, newowner);
    +
    + return argowner == current;
    +
    + /*
    + * In order to reschedule or handle a page fault, we need to drop the
    + * locks here. In the case of a fault, this gives the other task
    + * (either the highest priority waiter itself or the task which stole
    + * the rtmutex) the chance to try the fixup of the pi_state. So once we
    + * are back from handling the fault we need to check the pi_state after
    + * reacquiring the locks and before trying to do another fixup. When
    + * the fixup has been done already we simply return.
    + *
    + * Note: we hold both hb->lock and pi_mutex->wait_lock. We can safely
    + * drop hb->lock since the caller owns the hb -> futex_q relation.
    + * Dropping the pi_mutex->wait_lock requires the state revalidate.
    + */
    +handle_err:
    + raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    + spin_unlock(q->lock_ptr);
    +
    + switch (err) {
    + case -EFAULT:
    + err = fault_in_user_writeable(uaddr);
    + break;
    +
    + case -EAGAIN:
    + cond_resched();
    + err = 0;
    + break;
    +
    + default:
    + WARN_ON_ONCE(1);
    + break;
    + }
    +
    + spin_lock(q->lock_ptr);
    + raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    +
    + /*
    + * Check if someone else fixed it for us:
    + */
    + if (pi_state->owner != oldowner)
    + return argowner == current;
    +
    + /* Retry if err was -EAGAIN or the fault in succeeded */
    + if (!err)
    + goto retry;
    +
    + /*
    + * fault_in_user_writeable() failed so user state is immutable. At
    + * best we can make the kernel state consistent but user state will
    + * be most likely hosed and any subsequent unlock operation will be
    + * rejected due to PI futex rule [10].
    + *
    + * Ensure that the rtmutex owner is also the pi_state owner despite
    + * the user space value claiming something different. There is no
    + * point in unlocking the rtmutex if current is the owner as it
    + * would need to wait until the next waiter has taken the rtmutex
    + * to guarantee consistent state. Keep it simple. Userspace asked
    + * for this wreckaged state.
    + *
    + * The rtmutex has an owner - either current or some other
    + * task. See the EAGAIN loop above.
    + */
    + pi_state_update_owner(pi_state, rt_mutex_owner(&pi_state->pi_mutex));
    +
    + return err;
    +}
    +
    +static int fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
    + struct task_struct *argowner)
    +{
    + struct futex_pi_state *pi_state = q->pi_state;
    + int ret;
    +
    + lockdep_assert_held(q->lock_ptr);
    +
    + raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    + ret = __fixup_pi_state_owner(uaddr, q, argowner);
    + raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
    + return ret;
    +}
    +
    +static long futex_wait_restart(struct restart_block *restart);
    +
    +/**
    + * fixup_owner() - Post lock pi_state and corner case management
    + * @uaddr: user address of the futex
    + * @q: futex_q (contains pi_state and access to the rt_mutex)
    + * @locked: if the attempt to take the rt_mutex succeeded (1) or not (0)
    + *
    + * After attempting to lock an rt_mutex, this function is called to cleanup
    + * the pi_state owner as well as handle race conditions that may allow us to
    + * acquire the lock. Must be called with the hb lock held.
    + *
    + * Return:
    + * - 1 - success, lock taken;
    + * - 0 - success, lock not taken;
    + * - <0 - on error (-EFAULT)
    + */
    +static int fixup_owner(u32 __user *uaddr, struct futex_q *q, int locked)
    +{
    + if (locked) {
    + /*
    + * Got the lock. We might not be the anticipated owner if we
    + * did a lock-steal - fix up the PI-state in that case:
    + *
    + * Speculative pi_state->owner read (we don't hold wait_lock);
    + * since we own the lock pi_state->owner == current is the
    + * stable state, anything else needs more attention.
    + */
    + if (q->pi_state->owner != current)
    + return fixup_pi_state_owner(uaddr, q, current);
    + return 1;
    + }
    +
    + /*
    + * If we didn't get the lock; check if anybody stole it from us. In
    + * that case, we need to fix up the uval to point to them instead of
    + * us, otherwise bad things happen. [10]
    + *
    + * Another speculative read; pi_state->owner == current is unstable
    + * but needs our attention.
    + */
    + if (q->pi_state->owner == current)
    + return fixup_pi_state_owner(uaddr, q, NULL);
    +
    + /*
    + * Paranoia check. If we did not take the lock, then we should not be
    + * the owner of the rt_mutex. Warn and establish consistent state.
    + */
    + if (WARN_ON_ONCE(rt_mutex_owner(&q->pi_state->pi_mutex) == current))
    + return fixup_pi_state_owner(uaddr, q, current);
    +
    + return 0;
    +}
    +
    +/**
    + * futex_wait_queue_me() - queue_me() and wait for wakeup, timeout, or signal
    + * @hb: the futex hash bucket, must be locked by the caller
    + * @q: the futex_q to queue up on
    + * @timeout: the prepared hrtimer_sleeper, or null for no timeout
    + */
    +static void futex_wait_queue_me(struct futex_hash_bucket *hb, struct futex_q *q,
    + struct hrtimer_sleeper *timeout)
    +{
    + /*
    + * The task state is guaranteed to be set before another task can
    + * wake it. set_current_state() is implemented using smp_store_mb() and
    + * queue_me() calls spin_unlock() upon completion, both serializing
    + * access to the hash list and forcing another memory barrier.
    + */
    + set_current_state(TASK_INTERRUPTIBLE);
    + queue_me(q, hb);
    +
    + /* Arm the timer */
    + if (timeout)
    + hrtimer_sleeper_start_expires(timeout, HRTIMER_MODE_ABS);
    +
    + /*
    + * If we have been removed from the hash list, then another task
    + * has tried to wake us, and we can skip the call to schedule().
    + */
    + if (likely(!plist_node_empty(&q->list))) {
    + /*
    + * If the timer has already expired, current will already be
    + * flagged for rescheduling. Only call schedule if there
    + * is no timeout, or if it has yet to expire.
    + */
    + if (!timeout || timeout->task)
    + freezable_schedule();
    + }
    + __set_current_state(TASK_RUNNING);
    +}
    +
    +/**
    + * futex_wait_setup() - Prepare to wait on a futex
    + * @uaddr: the futex userspace address
    + * @val: the expected value
    + * @flags: futex flags (FLAGS_SHARED, etc.)
    + * @q: the associated futex_q
    + * @hb: storage for hash_bucket pointer to be returned to caller
    + *
    + * Setup the futex_q and locate the hash_bucket. Get the futex value and
    + * compare it with the expected value. Handle atomic faults internally.
    + * Return with the hb lock held on success, and unlocked on failure.
    + *
    + * Return:
    + * - 0 - uaddr contains val and hb has been locked;
    + * - <1 - -EFAULT or -EWOULDBLOCK (uaddr does not contain val) and hb is unlocked
    + */
    +static int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
    + struct futex_q *q, struct futex_hash_bucket **hb)
    +{
    + u32 uval;
    + int ret;
    +
    + /*
    + * Access the page AFTER the hash-bucket is locked.
    + * Order is important:
    + *
    + * Userspace waiter: val = var; if (cond(val)) futex_wait(&var, val);
    + * Userspace waker: if (cond(var)) { var = new; futex_wake(&var); }
    + *
    + * The basic logical guarantee of a futex is that it blocks ONLY
    + * if cond(var) is known to be true at the time of blocking, for
    + * any cond. If we locked the hash-bucket after testing *uaddr, that
    + * would open a race condition where we could block indefinitely with
    + * cond(var) false, which would violate the guarantee.
    + *
    + * On the other hand, we insert q and release the hash-bucket only
    + * after testing *uaddr. This guarantees that futex_wait() will NOT
    + * absorb a wakeup if *uaddr does not match the desired values
    + * while the syscall executes.
    + */
    +retry:
    + ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q->key, FUTEX_READ);
    + if (unlikely(ret != 0))
    + return ret;
    +
    +retry_private:
    + *hb = queue_lock(q);
    +
    + ret = get_futex_value_locked(&uval, uaddr);
    +
    + if (ret) {
    + queue_unlock(*hb);
    +
    + ret = get_user(uval, uaddr);
    + if (ret)
    + return ret;
    +
    + if (!(flags & FLAGS_SHARED))
    + goto retry_private;
    +
    + goto retry;
    + }
    +
    + if (uval != val) {
    + queue_unlock(*hb);
    + ret = -EWOULDBLOCK;
    + }
    +
    + return ret;
    +}
    +
    +static int futex_wait(u32 __user *uaddr, unsigned int flags, u32 val,
    + ktime_t *abs_time, u32 bitset)
    +{
    + struct hrtimer_sleeper timeout, *to;
    + struct restart_block *restart;
    + struct futex_hash_bucket *hb;
    + struct futex_q q = futex_q_init;
    + int ret;
    +
    + if (!bitset)
    + return -EINVAL;
    + q.bitset = bitset;
    +
    + to = futex_setup_timer(abs_time, &timeout, flags,
    + current->timer_slack_ns);
    +retry:
    + /*
    + * Prepare to wait on uaddr. On success, it holds hb->lock and q
    + * is initialized.
    + */
    + ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
    + if (ret)
    + goto out;
    +
    + /* queue_me and wait for wakeup, timeout, or a signal. */
    + futex_wait_queue_me(hb, &q, to);
    +
    + /* If we were woken (and unqueued), we succeeded, whatever. */
    + ret = 0;
    + if (!unqueue_me(&q))
    + goto out;
    + ret = -ETIMEDOUT;
    + if (to && !to->task)
    + goto out;
    +
    + /*
    + * We expect signal_pending(current), but we might be the
    + * victim of a spurious wakeup as well.
    + */
    + if (!signal_pending(current))
    + goto retry;
    +
    + ret = -ERESTARTSYS;
    + if (!abs_time)
    + goto out;
    +
    + restart = &current->restart_block;
    + restart->futex.uaddr = uaddr;
    + restart->futex.val = val;
    + restart->futex.time = *abs_time;
    + restart->futex.bitset = bitset;
    + restart->futex.flags = flags | FLAGS_HAS_TIMEOUT;
    +
    + ret = set_restart_fn(restart, futex_wait_restart);
    +
    +out:
    + if (to) {
    + hrtimer_cancel(&to->timer);
    + destroy_hrtimer_on_stack(&to->timer);
    + }
    + return ret;
    +}
    +
    +
    +static long futex_wait_restart(struct restart_block *restart)
    +{
    + u32 __user *uaddr = restart->futex.uaddr;
    + ktime_t t, *tp = NULL;
    +
    + if (restart->futex.flags & FLAGS_HAS_TIMEOUT) {
    + t = restart->futex.time;
    + tp = &t;
    + }
    + restart->fn = do_no_restart_syscall;
    +
    + return (long)futex_wait(uaddr, restart->futex.flags,
    + restart->futex.val, tp, restart->futex.bitset);
    +}
    +
    +
    +/*
    + * Userspace tried a 0 -> TID atomic transition of the futex value
    + * and failed. The kernel side here does the whole locking operation:
    + * if there are waiters then it will block as a consequence of relying
    + * on rt-mutexes, it does PI, etc. (Due to races the kernel might see
    + * a 0 value of the futex too.).
    + *
    + * Also serves as futex trylock_pi()'ing, and due semantics.
    + */
    +static int futex_lock_pi(u32 __user *uaddr, unsigned int flags,
    + ktime_t *time, int trylock)
    +{
    + struct hrtimer_sleeper timeout, *to;
    + struct task_struct *exiting = NULL;
    + struct rt_mutex_waiter rt_waiter;
    + struct futex_hash_bucket *hb;
    + struct futex_q q = futex_q_init;
    + int res, ret;
    +
    + if (!IS_ENABLED(CONFIG_FUTEX_PI))
    + return -ENOSYS;
    +
    + if (refill_pi_state_cache())
    + return -ENOMEM;
    +
    + to = futex_setup_timer(time, &timeout, flags, 0);
    +
    +retry:
    + ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &q.key, FUTEX_WRITE);
    + if (unlikely(ret != 0))
    + goto out;
    +
    +retry_private:
    + hb = queue_lock(&q);
    +
    + ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
    + &exiting, 0);
    + if (unlikely(ret)) {
    + /*
    + * Atomic work succeeded and we got the lock,
    + * or failed. Either way, we do _not_ block.
    + */
    + switch (ret) {
    + case 1:
    + /* We got the lock. */
    + ret = 0;
    + goto out_unlock_put_key;
    + case -EFAULT:
    + goto uaddr_faulted;
    + case -EBUSY:
    + case -EAGAIN:
    + /*
    + * Two reasons for this:
    + * - EBUSY: Task is exiting and we just wait for the
    + * exit to complete.
    + * - EAGAIN: The user space value changed.
    + */
    + queue_unlock(hb);
    + /*
    + * Handle the case where the owner is in the middle of
    + * exiting. Wait for the exit to complete otherwise
    + * this task might loop forever, aka. live lock.
    + */
    + wait_for_owner_exiting(ret, exiting);
    + cond_resched();
    + goto retry;
    + default:
    + goto out_unlock_put_key;
    + }
    + }
    +
    + WARN_ON(!q.pi_state);
    +
    + /*
    + * Only actually queue now that the atomic ops are done:
    + */
    + __queue_me(&q, hb);
    +
    + if (trylock) {
    + ret = rt_mutex_futex_trylock(&q.pi_state->pi_mutex);
    + /* Fixup the trylock return value: */
    + ret = ret ? 0 : -EWOULDBLOCK;
    + goto no_block;
    + }
    +
    + rt_mutex_init_waiter(&rt_waiter);
    +
    + /*
    + * On PREEMPT_RT_FULL, when hb->lock becomes an rt_mutex, we must not
    + * hold it while doing rt_mutex_start_proxy(), because then it will
    + * include hb->lock in the blocking chain, even through we'll not in
    + * fact hold it while blocking. This will lead it to report -EDEADLK
    + * and BUG when futex_unlock_pi() interleaves with this.
    + *
    + * Therefore acquire wait_lock while holding hb->lock, but drop the
    + * latter before calling __rt_mutex_start_proxy_lock(). This
    + * interleaves with futex_unlock_pi() -- which does a similar lock
    + * handoff -- such that the latter can observe the futex_q::pi_state
    + * before __rt_mutex_start_proxy_lock() is done.
    + */
    + raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
    + spin_unlock(q.lock_ptr);
    + /*
    + * __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
    + * such that futex_unlock_pi() is guaranteed to observe the waiter when
    + * it sees the futex_q::pi_state.
    + */
    + ret = __rt_mutex_start_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter, current);
    + raw_spin_unlock_irq(&q.pi_state->pi_mutex.wait_lock);
    +
    + if (ret) {
    + if (ret == 1)
    + ret = 0;
    + goto cleanup;
    + }
    +
    + if (unlikely(to))
    + hrtimer_sleeper_start_expires(to, HRTIMER_MODE_ABS);
    +
    + ret = rt_mutex_wait_proxy_lock(&q.pi_state->pi_mutex, to, &rt_waiter);
    +
    +cleanup:
    + spin_lock(q.lock_ptr);
    + /*
    + * If we failed to acquire the lock (deadlock/signal/timeout), we must
    + * first acquire the hb->lock before removing the lock from the
    + * rt_mutex waitqueue, such that we can keep the hb and rt_mutex wait
    + * lists consistent.
    + *
    + * In particular; it is important that futex_unlock_pi() can not
    + * observe this inconsistency.
    + */
    + if (ret && !rt_mutex_cleanup_proxy_lock(&q.pi_state->pi_mutex, &rt_waiter))
    + ret = 0;
    +
    +no_block:
    + /*
    + * Fixup the pi_state owner and possibly acquire the lock if we
    + * haven't already.
    + */
    + res = fixup_owner(uaddr, &q, !ret);
    + /*
    + * If fixup_owner() returned an error, propagate that. If it acquired
    + * the lock, clear our -ETIMEDOUT or -EINTR.
    + */
    + if (res)
    + ret = (res < 0) ? res : 0;
    +
    + unqueue_me_pi(&q);
    + spin_unlock(q.lock_ptr);
    + goto out;
    +
    +out_unlock_put_key:
    + queue_unlock(hb);
    +
    +out:
    + if (to) {
    + hrtimer_cancel(&to->timer);
    + destroy_hrtimer_on_stack(&to->timer);
    + }
    + return ret != -EINTR ? ret : -ERESTARTNOINTR;
    +
    +uaddr_faulted:
    + queue_unlock(hb);
    +
    + ret = fault_in_user_writeable(uaddr);
    + if (ret)
    + goto out;
    +
    + if (!(flags & FLAGS_SHARED))
    + goto retry_private;
    +
    + goto retry;
    +}
    +
    +/*
    + * Userspace attempted a TID -> 0 atomic transition, and failed.
    + * This is the in-kernel slowpath: we look up the PI state (if any),
    + * and do the rt-mutex unlock.
    + */
    +static int futex_unlock_pi(u32 __user *uaddr, unsigned int flags)
    +{
    + u32 curval, uval, vpid = task_pid_vnr(current);
    + union futex_key key = FUTEX_KEY_INIT;
    + struct futex_hash_bucket *hb;
    + struct futex_q *top_waiter;
    + int ret;
    +
    + if (!IS_ENABLED(CONFIG_FUTEX_PI))
    + return -ENOSYS;
    +
    +retry:
    + if (get_user(uval, uaddr))
    + return -EFAULT;
    + /*
    + * We release only a lock we actually own:
    + */
    + if ((uval & FUTEX_TID_MASK) != vpid)
    + return -EPERM;
    +
    + ret = get_futex_key(uaddr, flags & FLAGS_SHARED, &key, FUTEX_WRITE);
    + if (ret)
    + return ret;
    +
    + hb = hash_futex(&key);
    + spin_lock(&hb->lock);
    +
    + /*
    + * Check waiters first. We do not trust user space values at
    + * all and we at least want to know if user space fiddled
    + * with the futex value instead of blindly unlocking.
    + */
    + top_waiter = futex_top_waiter(hb, &key);
    + if (top_waiter) {
    + struct futex_pi_state *pi_state = top_waiter->pi_state;
    +
    + ret = -EINVAL;
    + if (!pi_state)
    + goto out_unlock;
    +
    + /*
    + * If current does not own the pi_state then the futex is
    + * inconsistent and user space fiddled with the futex value.
    + */
    + if (pi_state->owner != current)
    + goto out_unlock;
    +
    + get_pi_state(pi_state);
    + /*
    + * By taking wait_lock while still holding hb->lock, we ensure
    + * there is no point where we hold neither; and therefore
    + * wake_futex_pi() must observe a state consistent with what we
    + * observed.
    + *
    + * In particular; this forces __rt_mutex_start_proxy() to
    + * complete such that we're guaranteed to observe the
    + * rt_waiter. Also see the WARN in wake_futex_pi().
    + */
    + raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
    + spin_unlock(&hb->lock);
    +
    + /* drops pi_state->pi_mutex.wait_lock */
    + ret = wake_futex_pi(uaddr, uval, pi_state);
    +
    + put_pi_state(pi_state);
    +
    + /*
    + * Success, we're done! No tricky corner cases.
    + */
    + if (!ret)
    + return ret;
    + /*
    + * The atomic access to the futex value generated a
    + * pagefault, so retry the user-access and the wakeup:
    + */
    + if (ret == -EFAULT)
    + goto pi_faulted;
    + /*
    + * A unconditional UNLOCK_PI op raced against a waiter
    + * setting the FUTEX_WAITERS bit. Try again.
    + */
    + if (ret == -EAGAIN)
    + goto pi_retry;
    + /*
    + * wake_futex_pi has detected invalid state. Tell user
    + * space.
    + */
    + return ret;
    + }
    +
    + /*
    + * We have no kernel internal state, i.e. no waiters in the
    + * kernel. Waiters which are about to queue themselves are stuck
    + * on hb->lock. So we can safely ignore them. We do neither
    + * preserve the WAITERS bit not the OWNER_DIED one. We are the
    + * owner.
    + */
    + if ((ret = cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))) {
    + spin_unlock(&hb->lock);
    + switch (ret) {
    + case -EFAULT:
    + goto pi_faulted;
    +
    + case -EAGAIN:
    + goto pi_retry;
    +
    + default:
    + WARN_ON_ONCE(1);
    + return ret;
    + }
    + }
    +
    + /*
    + * If uval has changed, let user space handle it.
    + */
    + ret = (curval == uval) ? 0 : -EAGAIN;
    +
    +out_unlock:
    + spin_unlock(&hb->lock);
    + return ret;
    +
    +pi_retry:
    + cond_resched();
    + goto retry;
    +
    +pi_faulted:
    +
    + ret = fault_in_user_writeable(uaddr);
    + if (!ret)
    + goto retry;
    +
    + return ret;
    +}
    +
    +/**
    + * handle_early_requeue_pi_wakeup() - Handle early wakeup on the initial futex
    + * @hb: the hash_bucket futex_q was original enqueued on
    + * @q: the futex_q woken while waiting to be requeued
    + * @timeout: the timeout associated with the wait (NULL if none)
    + *
    + * Determine the cause for the early wakeup.
    + *
    + * Return:
    + * -EWOULDBLOCK or -ETIMEDOUT or -ERESTARTNOINTR
    + */
    +static inline
    +int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
    + struct futex_q *q,
    + struct hrtimer_sleeper *timeout)
    +{
    + int ret;
    +
    + /*
    + * With the hb lock held, we avoid races while we process the wakeup.
    + * We only need to hold hb (and not hb2) to ensure atomicity as the
    + * wakeup code can't change q.key from uaddr to uaddr2 if we hold hb.
    + * It can't be requeued from uaddr2 to something else since we don't
    + * support a PI aware source futex for requeue.
    + */
    + WARN_ON_ONCE(&hb->lock != q->lock_ptr);
    +
    + /*
    + * We were woken prior to requeue by a timeout or a signal.
    + * Unqueue the futex_q and determine which it was.
    + */
    + plist_del(&q->list, &hb->chain);
    + hb_waiters_dec(hb);
    +
    + /* Handle spurious wakeups gracefully */
    + ret = -EWOULDBLOCK;
    + if (timeout && !timeout->task)
    + ret = -ETIMEDOUT;
    + else if (signal_pending(current))
    + ret = -ERESTARTNOINTR;
    + return ret;
    +}
    +
    +/**
    + * futex_wait_requeue_pi() - Wait on uaddr and take uaddr2
    + * @uaddr: the futex we initially wait on (non-pi)
    + * @flags: futex flags (FLAGS_SHARED, FLAGS_CLOCKRT, etc.), they must be
    + * the same type, no requeueing from private to shared, etc.
    + * @val: the expected value of uaddr
    + * @abs_time: absolute timeout
    + * @bitset: 32 bit wakeup bitset set by userspace, defaults to all
    + * @uaddr2: the pi futex we will take prior to returning to user-space
    + *
    + * The caller will wait on uaddr and will be requeued by futex_requeue() to
    + * uaddr2 which must be PI aware and unique from uaddr. Normal wakeup will wake
    + * on uaddr2 and complete the acquisition of the rt_mutex prior to returning to
    + * userspace. This ensures the rt_mutex maintains an owner when it has waiters;
    + * without one, the pi logic would not know which task to boost/deboost, if
    + * there was a need to.
    + *
    + * We call schedule in futex_wait_queue_me() when we enqueue and return there
    + * via the following--
    + * 1) wakeup on uaddr2 after an atomic lock acquisition by futex_requeue()
    + * 2) wakeup on uaddr2 after a requeue
    + * 3) signal
    + * 4) timeout
    + *
    + * If 3, cleanup and return -ERESTARTNOINTR.
    + *
    + * If 2, we may then block on trying to take the rt_mutex and return via:
    + * 5) successful lock
    + * 6) signal
    + * 7) timeout
    + * 8) other lock acquisition failure
    + *
    + * If 6, return -EWOULDBLOCK (restarting the syscall would do the same).
    + *
    + * If 4 or 7, we cleanup and return with -ETIMEDOUT.
    + *
    + * Return:
    + * - 0 - On success;
    + * - <0 - On error
    + */
    +static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
    + u32 val, ktime_t *abs_time, u32 bitset,
    + u32 __user *uaddr2)
    +{
    + struct hrtimer_sleeper timeout, *to;
    + struct rt_mutex_waiter rt_waiter;
    + struct futex_hash_bucket *hb;
    + union futex_key key2 = FUTEX_KEY_INIT;
    + struct futex_q q = futex_q_init;
    + struct rt_mutex_base *pi_mutex;
    + int res, ret;
    +
    + if (!IS_ENABLED(CONFIG_FUTEX_PI))
    + return -ENOSYS;
    +
    + if (uaddr == uaddr2)
    + return -EINVAL;
    +
    + if (!bitset)
    + return -EINVAL;
    +
    + to = futex_setup_timer(abs_time, &timeout, flags,
    + current->timer_slack_ns);
    +
    + /*
    + * The waiter is allocated on our stack, manipulated by the requeue
    + * code while we sleep on uaddr.
    + */
    + rt_mutex_init_waiter(&rt_waiter);
    +
    + ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, FUTEX_WRITE);
    + if (unlikely(ret != 0))
    + goto out;
    +
    + q.bitset = bitset;
    + q.rt_waiter = &rt_waiter;
    + q.requeue_pi_key = &key2;
    +
    + /*
    + * Prepare to wait on uaddr. On success, it holds hb->lock and q
    + * is initialized.
    + */
    + ret = futex_wait_setup(uaddr, val, flags, &q, &hb);
    + if (ret)
    + goto out;
    +
    + /*
    + * The check above which compares uaddrs is not sufficient for
    + * shared futexes. We need to compare the keys:
    + */
    + if (match_futex(&q.key, &key2)) {
    + queue_unlock(hb);
    + ret = -EINVAL;
    + goto out;
    + }
    +
    + /* Queue the futex_q, drop the hb lock, wait for wakeup. */
    + futex_wait_queue_me(hb, &q, to);
    +
    + switch (futex_requeue_pi_wakeup_sync(&q)) {
    + case Q_REQUEUE_PI_IGNORE:
    + /* The waiter is still on uaddr1 */
    + spin_lock(&hb->lock);
    + ret = handle_early_requeue_pi_wakeup(hb, &q, to);
    + spin_unlock(&hb->lock);
    + break;
    +
    + case Q_REQUEUE_PI_LOCKED:
    + /* The requeue acquired the lock */
    + if (q.pi_state && (q.pi_state->owner != current)) {
    + spin_lock(q.lock_ptr);
    + ret = fixup_owner(uaddr2, &q, true);
    + /*
    + * Drop the reference to the pi state which the
    + * requeue_pi() code acquired for us.
    + */
    + put_pi_state(q.pi_state);
    + spin_unlock(q.lock_ptr);
    + /*
    + * Adjust the return value. It's either -EFAULT or
    + * success (1) but the caller expects 0 for success.
    + */
    + ret = ret < 0 ? ret : 0;
    + }
    + break;
    +
    + case Q_REQUEUE_PI_DONE:
    + /* Requeue completed. Current is 'pi_blocked_on' the rtmutex */
    + pi_mutex = &q.pi_state->pi_mutex;
    + ret = rt_mutex_wait_proxy_lock(pi_mutex, to, &rt_waiter);
    +
    + /* Current is not longer pi_blocked_on */
    + spin_lock(q.lock_ptr);
    + if (ret && !rt_mutex_cleanup_proxy_lock(pi_mutex, &rt_waiter))
    + ret = 0;
    +
    + debug_rt_mutex_free_waiter(&rt_waiter);
    + /*
    + * Fixup the pi_state owner and possibly acquire the lock if we
    + * haven't already.
    + */
    + res = fixup_owner(uaddr2, &q, !ret);
    + /*
    + * If fixup_owner() returned an error, propagate that. If it
    + * acquired the lock, clear -ETIMEDOUT or -EINTR.
    + */
    + if (res)
    + ret = (res < 0) ? res : 0;
    +
    + unqueue_me_pi(&q);
    + spin_unlock(q.lock_ptr);
    +
    + if (ret == -EINTR) {
    + /*
    + * We've already been requeued, but cannot restart
    + * by calling futex_lock_pi() directly. We could
    + * restart this syscall, but it would detect that
    + * the user space "val" changed and return
    + * -EWOULDBLOCK. Save the overhead of the restart
    + * and return -EWOULDBLOCK directly.
    + */
    + ret = -EWOULDBLOCK;
    + }
    + break;
    + default:
    + BUG();
    + }
    +
    +out:
    + if (to) {
    + hrtimer_cancel(&to->timer);
    + destroy_hrtimer_on_stack(&to->timer);
    + }
    + return ret;
    +}
    +
    +/*
    + * Support for robust futexes: the kernel cleans up held futexes at
    + * thread exit time.
    + *
    + * Implementation: user-space maintains a per-thread list of locks it
    + * is holding. Upon do_exit(), the kernel carefully walks this list,
    + * and marks all locks that are owned by this thread with the
    + * FUTEX_OWNER_DIED bit, and wakes up a waiter (if any). The list is
    + * always manipulated with the lock held, so the list is private and
    + * per-thread. Userspace also maintains a per-thread 'list_op_pending'
    + * field, to allow the kernel to clean up if the thread dies after
    + * acquiring the lock, but just before it could have added itself to
    + * the list. There can only be one such pending lock.
    + */
    +
    +/**
    + * sys_set_robust_list() - Set the robust-futex list head of a task
    + * @head: pointer to the list-head
    + * @len: length of the list-head, as userspace expects
    + */
    +SYSCALL_DEFINE2(set_robust_list, struct robust_list_head __user *, head,
    + size_t, len)
    +{
    + if (!futex_cmpxchg_enabled)
    + return -ENOSYS;
    + /*
    + * The kernel knows only one size for now:
    + */
    + if (unlikely(len != sizeof(*head)))
    + return -EINVAL;
    +
    + current->robust_list = head;
    +
    + return 0;
    +}
    +
    +/**
    + * sys_get_robust_list() - Get the robust-futex list head of a task
    + * @pid: pid of the process [zero for current task]
    + * @head_ptr: pointer to a list-head pointer, the kernel fills it in
    + * @len_ptr: pointer to a length field, the kernel fills in the header size
    + */
    +SYSCALL_DEFINE3(get_robust_list, int, pid,
    + struct robust_list_head __user * __user *, head_ptr,
    + size_t __user *, len_ptr)
    +{
    + struct robust_list_head __user *head;
    + unsigned long ret;
    + struct task_struct *p;
    +
    + if (!futex_cmpxchg_enabled)
    + return -ENOSYS;
    +
    + rcu_read_lock();
    +
    + ret = -ESRCH;
    + if (!pid)
    + p = current;
    + else {
    + p = find_task_by_vpid(pid);
    + if (!p)
    + goto err_unlock;
    + }
    +
    + ret = -EPERM;
    + if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
    + goto err_unlock;
    +
    + head = p->robust_list;
    + rcu_read_unlock();
    +
    + if (put_user(sizeof(*head), len_ptr))
    + return -EFAULT;
    + return put_user(head, head_ptr);
    +
    +err_unlock:
    + rcu_read_unlock();
    +
    + return ret;
    +}
    +
    +/* Constants for the pending_op argument of handle_futex_death */
    +#define HANDLE_DEATH_PENDING true
    +#define HANDLE_DEATH_LIST false
    +
    +/*
    + * Process a futex-list entry, check whether it's owned by the
    + * dying task, and do notification if so:
    + */
    +static int handle_futex_death(u32 __user *uaddr, struct task_struct *curr,
    + bool pi, bool pending_op)
    +{
    + u32 uval, nval, mval;
    + int err;
    +
    + /* Futex address must be 32bit aligned */
    + if ((((unsigned long)uaddr) % sizeof(*uaddr)) != 0)
    + return -1;
    +
    +retry:
    + if (get_user(uval, uaddr))
    + return -1;
    +
    + /*
    + * Special case for regular (non PI) futexes. The unlock path in
    + * user space has two race scenarios:
    + *
    + * 1. The unlock path releases the user space futex value and
    + * before it can execute the futex() syscall to wake up
    + * waiters it is killed.
    + *
    + * 2. A woken up waiter is killed before it can acquire the
    + * futex in user space.
    + *
    + * In both cases the TID validation below prevents a wakeup of
    + * potential waiters which can cause these waiters to block
    + * forever.
    + *
    + * In both cases the following conditions are met:
    + *
    + * 1) task->robust_list->list_op_pending != NULL
    + * @pending_op == true
    + * 2) User space futex value == 0
    + * 3) Regular futex: @pi == false
    + *
    + * If these conditions are met, it is safe to attempt waking up a
    + * potential waiter without touching the user space futex value and
    + * trying to set the OWNER_DIED bit. The user space futex value is
    + * uncontended and the rest of the user space mutex state is
    + * consistent, so a woken waiter will just take over the
    + * uncontended futex. Setting the OWNER_DIED bit would create
    + * inconsistent state and malfunction of the user space owner died
    + * handling.
    + */
    + if (pending_op && !pi && !uval) {
    + futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
    + return 0;
    + }
    +
    + if ((uval & FUTEX_TID_MASK) != task_pid_vnr(curr))
    + return 0;
    +
    + /*
    + * Ok, this dying thread is truly holding a futex
    + * of interest. Set the OWNER_DIED bit atomically
    + * via cmpxchg, and if the value had FUTEX_WAITERS
    + * set, wake up a waiter (if any). (We have to do a
    + * futex_wake() even if OWNER_DIED is already set -
    + * to handle the rare but possible case of recursive
    + * thread-death.) The rest of the cleanup is done in
    + * userspace.
    + */
    + mval = (uval & FUTEX_WAITERS) | FUTEX_OWNER_DIED;
    +
    + /*
    + * We are not holding a lock here, but we want to have
    + * the pagefault_disable/enable() protection because
    + * we want to handle the fault gracefully. If the
    + * access fails we try to fault in the futex with R/W
    + * verification via get_user_pages. get_user() above
    + * does not guarantee R/W access. If that fails we
    + * give up and leave the futex locked.
    + */
    + if ((err = cmpxchg_futex_value_locked(&nval, uaddr, uval, mval))) {
    + switch (err) {
    + case -EFAULT:
    + if (fault_in_user_writeable(uaddr))
    + return -1;
    + goto retry;
    +
    + case -EAGAIN:
    + cond_resched();
    + goto retry;
    +
    + default:
    + WARN_ON_ONCE(1);
    + return err;
    + }
    + }
    +
    + if (nval != uval)
    + goto retry;
    +
    + /*
    + * Wake robust non-PI futexes here. The wakeup of
    + * PI futexes happens in exit_pi_state():
    + */
    + if (!pi && (uval & FUTEX_WAITERS))
    + futex_wake(uaddr, 1, 1, FUTEX_BITSET_MATCH_ANY);
    +
    + return 0;
    +}
    +
    +/*
    + * Fetch a robust-list pointer. Bit 0 signals PI futexes:
    + */
    +static inline int fetch_robust_entry(struct robust_list __user **entry,
    + struct robust_list __user * __user *head,
    + unsigned int *pi)
    +{
    + unsigned long uentry;
    +
    + if (get_user(uentry, (unsigned long __user *)head))
    + return -EFAULT;
    +
    + *entry = (void __user *)(uentry & ~1UL);
    + *pi = uentry & 1;
    +
    + return 0;
    +}
    +
    +/*
    + * Walk curr->robust_list (very carefully, it's a userspace list!)
    + * and mark any locks found there dead, and notify any waiters.
    + *
    + * We silently return on any sign of list-walking problem.
    + */
    +static void exit_robust_list(struct task_struct *curr)
    +{
    + struct robust_list_head __user *head = curr->robust_list;
    + struct robust_list __user *entry, *next_entry, *pending;
    + unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
    + unsigned int next_pi;
    + unsigned long futex_offset;
    + int rc;
    +
    + if (!futex_cmpxchg_enabled)
    + return;
    +
    + /*
    + * Fetch the list head (which was registered earlier, via
    + * sys_set_robust_list()):
    + */
    + if (fetch_robust_entry(&entry, &head->list.next, &pi))
    + return;
    + /*
    + * Fetch the relative futex offset:
    + */
    + if (get_user(futex_offset, &head->futex_offset))
    + return;
    + /*
    + * Fetch any possibly pending lock-add first, and handle it
    + * if it exists:
    + */
    + if (fetch_robust_entry(&pending, &head->list_op_pending, &pip))
    + return;
    +
    + next_entry = NULL; /* avoid warning with gcc */
    + while (entry != &head->list) {
    + /*
    + * Fetch the next entry in the list before calling
    + * handle_futex_death:
    + */
    + rc = fetch_robust_entry(&next_entry, &entry->next, &next_pi);
    + /*
    + * A pending lock might already be on the list, so
    + * don't process it twice:
    + */
    + if (entry != pending) {
    + if (handle_futex_death((void __user *)entry + futex_offset,
    + curr, pi, HANDLE_DEATH_LIST))
    + return;
    + }
    + if (rc)
    + return;
    + entry = next_entry;
    + pi = next_pi;
    + /*
    + * Avoid excessively long or circular lists:
    + */
    + if (!--limit)
    + break;
    +
    + cond_resched();
    + }
    +
    + if (pending) {
    + handle_futex_death((void __user *)pending + futex_offset,
    + curr, pip, HANDLE_DEATH_PENDING);
    + }
    +}
    +
    +static void futex_cleanup(struct task_struct *tsk)
    +{
    + if (unlikely(tsk->robust_list)) {
    + exit_robust_list(tsk);
    + tsk->robust_list = NULL;
    + }
    +
    +#ifdef CONFIG_COMPAT
    + if (unlikely(tsk->compat_robust_list)) {
    + compat_exit_robust_list(tsk);
    + tsk->compat_robust_list = NULL;
    + }
    +#endif
    +
    + if (unlikely(!list_empty(&tsk->pi_state_list)))
    + exit_pi_state_list(tsk);
    +}
    +
    +/**
    + * futex_exit_recursive - Set the tasks futex state to FUTEX_STATE_DEAD
    + * @tsk: task to set the state on
    + *
    + * Set the futex exit state of the task lockless. The futex waiter code
    + * observes that state when a task is exiting and loops until the task has
    + * actually finished the futex cleanup. The worst case for this is that the
    + * waiter runs through the wait loop until the state becomes visible.
    + *
    + * This is called from the recursive fault handling path in do_exit().
    + *
    + * This is best effort. Either the futex exit code has run already or
    + * not. If the OWNER_DIED bit has been set on the futex then the waiter can
    + * take it over. If not, the problem is pushed back to user space. If the
    + * futex exit code did not run yet, then an already queued waiter might
    + * block forever, but there is nothing which can be done about that.
    + */
    +void futex_exit_recursive(struct task_struct *tsk)
    +{
    + /* If the state is FUTEX_STATE_EXITING then futex_exit_mutex is held */
    + if (tsk->futex_state == FUTEX_STATE_EXITING)
    + mutex_unlock(&tsk->futex_exit_mutex);
    + tsk->futex_state = FUTEX_STATE_DEAD;
    +}
    +
    +static void futex_cleanup_begin(struct task_struct *tsk)
    +{
    + /*
    + * Prevent various race issues against a concurrent incoming waiter
    + * including live locks by forcing the waiter to block on
    + * tsk->futex_exit_mutex when it observes FUTEX_STATE_EXITING in
    + * attach_to_pi_owner().
    + */
    + mutex_lock(&tsk->futex_exit_mutex);
    +
    + /*
    + * Switch the state to FUTEX_STATE_EXITING under tsk->pi_lock.
    + *
    + * This ensures that all subsequent checks of tsk->futex_state in
    + * attach_to_pi_owner() must observe FUTEX_STATE_EXITING with
    + * tsk->pi_lock held.
    + *
    + * It guarantees also that a pi_state which was queued right before
    + * the state change under tsk->pi_lock by a concurrent waiter must
    + * be observed in exit_pi_state_list().
    + */
    + raw_spin_lock_irq(&tsk->pi_lock);
    + tsk->futex_state = FUTEX_STATE_EXITING;
    + raw_spin_unlock_irq(&tsk->pi_lock);
    +}
    +
    +static void futex_cleanup_end(struct task_struct *tsk, int state)
    +{
    + /*
    + * Lockless store. The only side effect is that an observer might
    + * take another loop until it becomes visible.
    + */
    + tsk->futex_state = state;
    + /*
    + * Drop the exit protection. This unblocks waiters which observed
    + * FUTEX_STATE_EXITING to reevaluate the state.
    + */
    + mutex_unlock(&tsk->futex_exit_mutex);
    +}
    +
    +void futex_exec_release(struct task_struct *tsk)
    +{
    + /*
    + * The state handling is done for consistency, but in the case of
    + * exec() there is no way to prevent further damage as the PID stays
    + * the same. But for the unlikely and arguably buggy case that a
    + * futex is held on exec(), this provides at least as much state
    + * consistency protection which is possible.
    + */
    + futex_cleanup_begin(tsk);
    + futex_cleanup(tsk);
    + /*
    + * Reset the state to FUTEX_STATE_OK. The task is alive and about
    + * exec a new binary.
    + */
    + futex_cleanup_end(tsk, FUTEX_STATE_OK);
    +}
    +
    +void futex_exit_release(struct task_struct *tsk)
    +{
    + futex_cleanup_begin(tsk);
    + futex_cleanup(tsk);
    + futex_cleanup_end(tsk, FUTEX_STATE_DEAD);
    +}
    +
    +long do_futex(u32 __user *uaddr, int op, u32 val, ktime_t *timeout,
    + u32 __user *uaddr2, u32 val2, u32 val3)
    +{
    + int cmd = op & FUTEX_CMD_MASK;
    + unsigned int flags = 0;
    +
    + if (!(op & FUTEX_PRIVATE_FLAG))
    + flags |= FLAGS_SHARED;
    +
    + if (op & FUTEX_CLOCK_REALTIME) {
    + flags |= FLAGS_CLOCKRT;
    + if (cmd != FUTEX_WAIT_BITSET && cmd != FUTEX_WAIT_REQUEUE_PI &&
    + cmd != FUTEX_LOCK_PI2)
    + return -ENOSYS;
    + }
    +
    + switch (cmd) {
    + case FUTEX_LOCK_PI:
    + case FUTEX_LOCK_PI2:
    + case FUTEX_UNLOCK_PI:
    + case FUTEX_TRYLOCK_PI:
    + case FUTEX_WAIT_REQUEUE_PI:
    + case FUTEX_CMP_REQUEUE_PI:
    + if (!futex_cmpxchg_enabled)
    + return -ENOSYS;
    + }
    +
    + switch (cmd) {
    + case FUTEX_WAIT:
    + val3 = FUTEX_BITSET_MATCH_ANY;
    + fallthrough;
    + case FUTEX_WAIT_BITSET:
    + return futex_wait(uaddr, flags, val, timeout, val3);
    + case FUTEX_WAKE:
    + val3 = FUTEX_BITSET_MATCH_ANY;
    + fallthrough;
    + case FUTEX_WAKE_BITSET:
    + return futex_wake(uaddr, flags, val, val3);
    + case FUTEX_REQUEUE:
    + return futex_requeue(uaddr, flags, uaddr2, val, val2, NULL, 0);
    + case FUTEX_CMP_REQUEUE:
    + return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 0);
    + case FUTEX_WAKE_OP:
    + return futex_wake_op(uaddr, flags, uaddr2, val, val2, val3);
    + case FUTEX_LOCK_PI:
    + flags |= FLAGS_CLOCKRT;
    + fallthrough;
    + case FUTEX_LOCK_PI2:
    + return futex_lock_pi(uaddr, flags, timeout, 0);
    + case FUTEX_UNLOCK_PI:
    + return futex_unlock_pi(uaddr, flags);
    + case FUTEX_TRYLOCK_PI:
    + return futex_lock_pi(uaddr, flags, NULL, 1);
    + case FUTEX_WAIT_REQUEUE_PI:
    + val3 = FUTEX_BITSET_MATCH_ANY;
    + return futex_wait_requeue_pi(uaddr, flags, val, timeout, val3,
    + uaddr2);
    + case FUTEX_CMP_REQUEUE_PI:
    + return futex_requeue(uaddr, flags, uaddr2, val, val2, &val3, 1);
    + }
    + return -ENOSYS;
    +}
    +
    +static __always_inline bool futex_cmd_has_timeout(u32 cmd)
    +{
    + switch (cmd) {
    + case FUTEX_WAIT:
    + case FUTEX_LOCK_PI:
    + case FUTEX_LOCK_PI2:
    + case FUTEX_WAIT_BITSET:
    + case FUTEX_WAIT_REQUEUE_PI:
    + return true;
    + }
    + return false;
    +}
    +
    +static __always_inline int
    +futex_init_timeout(u32 cmd, u32 op, struct timespec64 *ts, ktime_t *t)
    +{
    + if (!timespec64_valid(ts))
    + return -EINVAL;
    +
    + *t = timespec64_to_ktime(*ts);
    + if (cmd == FUTEX_WAIT)
    + *t = ktime_add_safe(ktime_get(), *t);
    + else if (cmd != FUTEX_LOCK_PI && !(op & FUTEX_CLOCK_REALTIME))
    + *t = timens_ktime_to_host(CLOCK_MONOTONIC, *t);
    + return 0;
    +}
    +
    +SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val,
    + const struct __kernel_timespec __user *, utime,
    + u32 __user *, uaddr2, u32, val3)
    +{
    + int ret, cmd = op & FUTEX_CMD_MASK;
    + ktime_t t, *tp = NULL;
    + struct timespec64 ts;
    +
    + if (utime && futex_cmd_has_timeout(cmd)) {
    + if (unlikely(should_fail_futex(!(op & FUTEX_PRIVATE_FLAG))))
    + return -EFAULT;
    + if (get_timespec64(&ts, utime))
    + return -EFAULT;
    + ret = futex_init_timeout(cmd, op, &ts, &t);
    + if (ret)
    + return ret;
    + tp = &t;
    + }
    +
    + return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
    +}
    +
    +#ifdef CONFIG_COMPAT
    +/*
    + * Fetch a robust-list pointer. Bit 0 signals PI futexes:
    + */
    +static inline int
    +compat_fetch_robust_entry(compat_uptr_t *uentry, struct robust_list __user **entry,
    + compat_uptr_t __user *head, unsigned int *pi)
    +{
    + if (get_user(*uentry, head))
    + return -EFAULT;
    +
    + *entry = compat_ptr((*uentry) & ~1);
    + *pi = (unsigned int)(*uentry) & 1;
    +
    + return 0;
    +}
    +
    +static void __user *futex_uaddr(struct robust_list __user *entry,
    + compat_long_t futex_offset)
    +{
    + compat_uptr_t base = ptr_to_compat(entry);
    + void __user *uaddr = compat_ptr(base + futex_offset);
    +
    + return uaddr;
    +}
    +
    +/*
    + * Walk curr->robust_list (very carefully, it's a userspace list!)
    + * and mark any locks found there dead, and notify any waiters.
    + *
    + * We silently return on any sign of list-walking problem.
    + */
    +static void compat_exit_robust_list(struct task_struct *curr)
    +{
    + struct compat_robust_list_head __user *head = curr->compat_robust_list;
    + struct robust_list __user *entry, *next_entry, *pending;
    + unsigned int limit = ROBUST_LIST_LIMIT, pi, pip;
    + unsigned int next_pi;
    + compat_uptr_t uentry, next_uentry, upending;
    + compat_long_t futex_offset;
    + int rc;
    +
    + if (!futex_cmpxchg_enabled)
    + return;
    +
    + /*
    + * Fetch the list head (which was registered earlier, via
    + * sys_set_robust_list()):
    + */
    + if (compat_fetch_robust_entry(&uentry, &entry, &head->list.next, &pi))
    + return;
    + /*
    + * Fetch the relative futex offset:
    + */
    + if (get_user(futex_offset, &head->futex_offset))
    + return;
    + /*
    + * Fetch any possibly pending lock-add first, and handle it
    + * if it exists:
    + */
    + if (compat_fetch_robust_entry(&upending, &pending,
    + &head->list_op_pending, &pip))
    + return;
    +
    + next_entry = NULL; /* avoid warning with gcc */
    + while (entry != (struct robust_list __user *) &head->list) {
    + /*
    + * Fetch the next entry in the list before calling
    + * handle_futex_death:
    + */
    + rc = compat_fetch_robust_entry(&next_uentry, &next_entry,
    + (compat_uptr_t __user *)&entry->next, &next_pi);
    + /*
    + * A pending lock might already be on the list, so
    + * dont process it twice:
    + */
    + if (entry != pending) {
    + void __user *uaddr = futex_uaddr(entry, futex_offset);
    +
    + if (handle_futex_death(uaddr, curr, pi,
    + HANDLE_DEATH_LIST))
    + return;
    + }
    + if (rc)
    + return;
    + uentry = next_uentry;
    + entry = next_entry;
    + pi = next_pi;
    + /*
    + * Avoid excessively long or circular lists:
    + */
    + if (!--limit)
    + break;
    +
    + cond_resched();
    + }
    + if (pending) {
    + void __user *uaddr = futex_uaddr(pending, futex_offset);
    +
    + handle_futex_death(uaddr, curr, pip, HANDLE_DEATH_PENDING);
    + }
    +}
    +
    +COMPAT_SYSCALL_DEFINE2(set_robust_list,
    + struct compat_robust_list_head __user *, head,
    + compat_size_t, len)
    +{
    + if (!futex_cmpxchg_enabled)
    + return -ENOSYS;
    +
    + if (unlikely(len != sizeof(*head)))
    + return -EINVAL;
    +
    + current->compat_robust_list = head;
    +
    + return 0;
    +}
    +
    +COMPAT_SYSCALL_DEFINE3(get_robust_list, int, pid,
    + compat_uptr_t __user *, head_ptr,
    + compat_size_t __user *, len_ptr)
    +{
    + struct compat_robust_list_head __user *head;
    + unsigned long ret;
    + struct task_struct *p;
    +
    + if (!futex_cmpxchg_enabled)
    + return -ENOSYS;
    +
    + rcu_read_lock();
    +
    + ret = -ESRCH;
    + if (!pid)
    + p = current;
    + else {
    + p = find_task_by_vpid(pid);
    + if (!p)
    + goto err_unlock;
    + }
    +
    + ret = -EPERM;
    + if (!ptrace_may_access(p, PTRACE_MODE_READ_REALCREDS))
    + goto err_unlock;
    +
    + head = p->compat_robust_list;
    + rcu_read_unlock();
    +
    + if (put_user(sizeof(*head), len_ptr))
    + return -EFAULT;
    + return put_user(ptr_to_compat(head), head_ptr);
    +
    +err_unlock:
    + rcu_read_unlock();
    +
    + return ret;
    +}
    +#endif /* CONFIG_COMPAT */
    +
    +#ifdef CONFIG_COMPAT_32BIT_TIME
    +SYSCALL_DEFINE6(futex_time32, u32 __user *, uaddr, int, op, u32, val,
    + const struct old_timespec32 __user *, utime, u32 __user *, uaddr2,
    + u32, val3)
    +{
    + int ret, cmd = op & FUTEX_CMD_MASK;
    + ktime_t t, *tp = NULL;
    + struct timespec64 ts;
    +
    + if (utime && futex_cmd_has_timeout(cmd)) {
    + if (get_old_timespec32(&ts, utime))
    + return -EFAULT;
    + ret = futex_init_timeout(cmd, op, &ts, &t);
    + if (ret)
    + return ret;
    + tp = &t;
    + }
    +
    + return do_futex(uaddr, op, val, tp, uaddr2, (unsigned long)utime, val3);
    +}
    +#endif /* CONFIG_COMPAT_32BIT_TIME */
    +
    +static void __init futex_detect_cmpxchg(void)
    +{
    +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
    + u32 curval;
    +
    + /*
    + * This will fail and we want it. Some arch implementations do
    + * runtime detection of the futex_atomic_cmpxchg_inatomic()
    + * functionality. We want to know that before we call in any
    + * of the complex code paths. Also we want to prevent
    + * registration of robust lists in that case. NULL is
    + * guaranteed to fault and we get -EFAULT on functional
    + * implementation, the non-functional ones will return
    + * -ENOSYS.
    + */
    + if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT)
    + futex_cmpxchg_enabled = 1;
    +#endif
    +}
    +
    +static int __init futex_init(void)
    +{
    + unsigned int futex_shift;
    + unsigned long i;
    +
    +#if CONFIG_BASE_SMALL
    + futex_hashsize = 16;
    +#else
    + futex_hashsize = roundup_pow_of_two(256 * num_possible_cpus());
    +#endif
    +
    + futex_queues = alloc_large_system_hash("futex", sizeof(*futex_queues),
    + futex_hashsize, 0,
    + futex_hashsize < 256 ? HASH_SMALL : 0,
    + &futex_shift, NULL,
    + futex_hashsize, futex_hashsize);
    + futex_hashsize = 1UL << futex_shift;
    +
    + futex_detect_cmpxchg();
    +
    + for (i = 0; i < futex_hashsize; i++) {
    + atomic_set(&futex_queues[i].waiters, 0);
    + plist_head_init(&futex_queues[i].chain);
    + spin_lock_init(&futex_queues[i].lock);
    + }
    +
    + return 0;
    +}
    +core_initcall(futex_init);
    \
     
     \ /
      Last update: 2021-10-09 12:09    [W:5.987 / U:0.056 seconds]
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