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SubjectRe: [PATCH v2] mm/oom_kill: wake futex waiters before annihilating victim shared mutex
> I am afraid we can't call futex_exit_release() under rcu_read_lock()
> because it might sleep.

Ah that's too bad. Is there an equivalent atomic call suitable for this purpose?

>
> BUG: sleeping function called from invalid context at kernel/locking/mutex.c:577
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1509, name: lsbug
> preempt_count: 1, expected: 0
> 3 locks held by lsbug/1509:
> #0: ffff00004de99c98 (&mm->mmap_lock){++++}-{3:3}, at: do_page_fault
> #1: ffff800010fd8308 (oom_lock){+.+.}-{3:3}, at: __alloc_pages_slowpath.constprop.0
> __alloc_pages_may_oom at /usr/src/linux-next/mm/page_alloc.c:4278
> (inlined by) __alloc_pages_slowpath at /usr/src/linux-next/mm/page_alloc.c:5058
> #2: ffff000867b3b0c0 (&p->alloc_lock){+.+.}-{2:2}, at: find_lock_task_mm
> find_lock_task_mm at /usr/src/linux-next/mm/oom_kill.c:145
> CPU: 5 PID: 1509 Comm: lsbug Not tainted 5.16.0-rc5-next-20211214+ #172
> Hardware name: MiTAC RAPTOR EV-883832-X3-0001/RAPTOR, BIOS 1.6 06/28/2020
> Call trace:
> dump_backtrace
> show_stack
> dump_stack_lvl
> dump_stack
> __might_resched
> __might_sleep
> __mutex_lock
> mutex_lock_nested
> futex_cleanup_begin
> futex_cleanup_begin at /usr/src/linux-next/kernel/futex/core.c:1071
> futex_exit_release
> __oom_kill_process
> oom_kill_process
> out_of_memory
> __alloc_pages_slowpath.constprop.0
> __alloc_pages
> alloc_pages_vma
> alloc_zeroed_user_highpage_movable
> do_anonymous_page
> __handle_mm_fault
> handle_mm_fault
> do_page_fault
> do_translation_fault
> do_mem_abort
> el0_da
> el0t_64_sync_handler
> el0t_64_sync
> =============================
> [ BUG: Invalid wait context ]
> 5.16.0-rc5-next-20211214+ #172 Tainted: G W
> -----------------------------
> lsbug/1509 is trying to lock:
> ffff000867b3ba98 (&tsk->futex_exit_mutex){+.+.}-{3:3}, at: futex_cleanup_begin
> other info that might help us debug this:
> context-{4:4}
> 3 locks held by lsbug/1509:
> #0: ffff00004de99c98 (&mm->mmap_lock){++++}-{3:3}, at: do_page_fault
> #1: ffff800010fd8308 (oom_lock){+.+.}-{3:3}, at: __alloc_pages_slowpath.constprop.0
> #2: ffff000867b3b0c0 (&p->alloc_lock){+.+.}-{2:2}, at: find_lock_task_mm
> stack backtrace:
> CPU: 5 PID: 1509 Comm: lsbug Tainted: G W 5.16.0-rc5-next-20211214+ #172
> Hardware name: MiTAC RAPTOR EV-883832-X3-0001/RAPTOR, BIOS 1.6 06/28/2020
> Call trace:
> dump_backtrace
> show_stack
> dump_stack_lvl
> dump_stack
> __lock_acquire
> lock_acquire
> __mutex_lock
> mutex_lock_nested
> futex_cleanup_begin
> futex_exit_release
> __oom_kill_process
> oom_kill_process
> out_of_memory
> __alloc_pages_slowpath.constprop.0
> __alloc_pages
> alloc_pages_vma
> alloc_zeroed_user_highpage_movable
> do_anonymous_page
> __handle_mm_fault
> handle_mm_fault
> do_page_fault
> do_translation_fault
> do_mem_abort
> el0_da
> el0t_64_sync_handler
> el0t_64_sync
>
> > ---
> > mm/oom_kill.c | 12 ++++++++++++
> > 1 file changed, 12 insertions(+)
> >
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 1ddabefcfb5a..884a5f15fd06 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -44,6 +44,7 @@
> > #include <linux/kthread.h>
> > #include <linux/init.h>
> > #include <linux/mmu_notifier.h>
> > +#include <linux/futex.h>
> >
> > #include <asm/tlb.h>
> > #include "internal.h"
> > @@ -885,6 +886,11 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
> > count_vm_event(OOM_KILL);
> > memcg_memory_event_mm(mm, MEMCG_OOM_KILL);
> >
> > + /*
> > + * We call futex_exit_release() on the victim task to ensure any waiters on any
> > + * process-shared futexes held by the victim task are woken up.
> > + */
> > + futex_exit_release(victim);
> > /*
> > * We should send SIGKILL before granting access to memory reserves
> > * in order to prevent the OOM victim from depleting the memory
> > @@ -930,6 +936,12 @@ static void __oom_kill_process(struct task_struct *victim, const char *message)
> > */
> > if (unlikely(p->flags & PF_KTHREAD))
> > continue;
> > + /*
> > + * We call futex_exit_release() on any task p sharing the
> > + * victim->mm to ensure any waiters on any
> > + * process-shared futexes held by task p are woken up.
> > + */
> > + futex_exit_release(p);
> > do_send_sig_info(SIGKILL, SEND_SIG_PRIV, p, PIDTYPE_TGID);
> > }
> > rcu_read_unlock();
> > --
> > 2.27.0
> >
>

Best,
Joel Savitz

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