Messages in this thread Patch in this message | | | Date | Tue, 19 Dec 2023 16:18:16 -0800 | Subject | [PATCH v7 05/23] locking/mutex: Rework task_struct::blocked_on | From | John Stultz <> |
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From: Peter Zijlstra <peterz@infradead.org>
Track the blocked-on relation for mutexes, to allow following this relation at schedule time.
task | blocked-on v mutex | owner v task
Also adds a blocked_on_state value so we can distinguqish when a task is blocked_on a mutex, but is either blocked, waking up, or runnable (such that it can try to aquire the lock its blocked on).
This avoids some of the subtle & racy games where the blocked_on state gets cleared, only to have it re-added by the mutex_lock_slowpath call when it tries to aquire the lock on wakeup
Also adds blocked_lock to the task_struct so we can safely serialize the blocked-on state.
Finally adds wrappers that are useful to provide correctness checks. Folded in from a patch by: Valentin Schneider <valentin.schneider@arm.com>
This all will be used for tracking blocked-task/mutex chains with the prox-execution patch in a similar fashion to how priority inheritence is done with rt_mutexes.
Cc: Joel Fernandes <joelaf@google.com> Cc: Qais Yousef <qyousef@google.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Valentin Schneider <vschneid@redhat.com> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Ben Segall <bsegall@google.com> Cc: Zimuzo Ezeozue <zezeozue@google.com> Cc: Youssef Esmat <youssefesmat@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Will Deacon <will@kernel.org> Cc: Waiman Long <longman@redhat.com> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Metin Kaya <Metin.Kaya@arm.com> Cc: Xuewen Yan <xuewen.yan94@gmail.com> Cc: K Prateek Nayak <kprateek.nayak@amd.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: kernel-team@android.com Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> [minor changes while rebasing] Signed-off-by: Juri Lelli <juri.lelli@redhat.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Connor O'Brien <connoro@google.com> [jstultz: Fix blocked_on tracking in __mutex_lock_common in error paths] Signed-off-by: John Stultz <jstultz@google.com> --- v2: * Fixed blocked_on tracking in error paths that was causing crashes v4: * Ensure we clear blocked_on when waking ww_mutexes to die or wound. This is critical so we don't get ciruclar blocked_on relationships that can't be resolved. v5: * Fix potential bug where the skip_wait path might clear blocked_on when that path never set it * Slight tweaks to where we set blocked_on to make it consistent, along with extra WARN_ON correctness checking * Minor comment changes v7: * Minor commit message change suggested by Metin Kaya * Fix WARN_ON conditionals in unlock path (as blocked_on might already be cleared), found while looking at issue Metin Kaya raised. * Minor tweaks to be consistent in what we do under the blocked_on lock, also tweaked variable name to avoid confusion with label, and comment typos, as suggested by Metin Kaya * Minor tweak for CONFIG_SCHED_PROXY_EXEC name change * Moved unused block of code to later in the series, as suggested by Metin Kaya * Switch to a tri-state to be able to distinguish from waking and runnable so we can later safely do return migration from ttwu * Folded together with related blocked_on changes --- include/linux/sched.h | 40 ++++++++++++++++++++++++++++++++---- init/init_task.c | 1 + kernel/fork.c | 4 ++-- kernel/locking/mutex-debug.c | 9 ++++---- kernel/locking/mutex.c | 35 +++++++++++++++++++++++++++---- kernel/locking/ww_mutex.h | 24 ++++++++++++++++++++-- kernel/sched/core.c | 6 ++++++ 7 files changed, 103 insertions(+), 16 deletions(-)
diff --git a/include/linux/sched.h b/include/linux/sched.h index 1e80c330f755..bfe8670f99a1 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -743,6 +743,12 @@ struct kmap_ctrl { #endif }; +enum blocked_on_state { + BO_RUNNABLE, + BO_BLOCKED, + BO_WAKING, +}; + struct task_struct { #ifdef CONFIG_THREAD_INFO_IN_TASK /* @@ -1149,10 +1155,9 @@ struct task_struct { struct rt_mutex_waiter *pi_blocked_on; #endif -#ifdef CONFIG_DEBUG_MUTEXES - /* Mutex deadlock detection: */ - struct mutex_waiter *blocked_on; -#endif + enum blocked_on_state blocked_on_state; + struct mutex *blocked_on; /* lock we're blocked on */ + raw_spinlock_t blocked_lock; #ifdef CONFIG_DEBUG_ATOMIC_SLEEP int non_block_count; @@ -2258,6 +2263,33 @@ static inline int rwlock_needbreak(rwlock_t *lock) #endif } +static inline void set_task_blocked_on(struct task_struct *p, struct mutex *m) +{ + lockdep_assert_held(&p->blocked_lock); + + /* + * Check we are clearing values to NULL or setting NULL + * to values to ensure we don't overwrite exisiting mutex + * values or clear already cleared values + */ + WARN_ON((!m && !p->blocked_on) || (m && p->blocked_on)); + + p->blocked_on = m; + p->blocked_on_state = m ? BO_BLOCKED : BO_RUNNABLE; +} + +static inline struct mutex *get_task_blocked_on(struct task_struct *p) +{ + lockdep_assert_held(&p->blocked_lock); + + return p->blocked_on; +} + +static inline struct mutex *get_task_blocked_on_once(struct task_struct *p) +{ + return READ_ONCE(p->blocked_on); +} + static __always_inline bool need_resched(void) { return unlikely(tif_need_resched()); diff --git a/init/init_task.c b/init/init_task.c index 5727d42149c3..0c31d7d7c7a9 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -131,6 +131,7 @@ struct task_struct init_task .journal_info = NULL, INIT_CPU_TIMERS(init_task) .pi_lock = __RAW_SPIN_LOCK_UNLOCKED(init_task.pi_lock), + .blocked_lock = __RAW_SPIN_LOCK_UNLOCKED(init_task.blocked_lock), .timer_slack_ns = 50000, /* 50 usec default slack */ .thread_pid = &init_struct_pid, .thread_node = LIST_HEAD_INIT(init_signals.thread_head), diff --git a/kernel/fork.c b/kernel/fork.c index 10917c3e1f03..b3ba3d22d8b2 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2358,6 +2358,7 @@ __latent_entropy struct task_struct *copy_process( ftrace_graph_init_task(p); rt_mutex_init_task(p); + raw_spin_lock_init(&p->blocked_lock); lockdep_assert_irqs_enabled(); #ifdef CONFIG_PROVE_LOCKING @@ -2456,9 +2457,8 @@ __latent_entropy struct task_struct *copy_process( lockdep_init_task(p); #endif -#ifdef CONFIG_DEBUG_MUTEXES + p->blocked_on_state = BO_RUNNABLE; p->blocked_on = NULL; /* not blocked yet */ -#endif #ifdef CONFIG_BCACHE p->sequential_io = 0; p->sequential_io_avg = 0; diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c index bc8abb8549d2..1eedf7c60c00 100644 --- a/kernel/locking/mutex-debug.c +++ b/kernel/locking/mutex-debug.c @@ -52,17 +52,18 @@ void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter, { lockdep_assert_held(&lock->wait_lock); - /* Mark the current thread as blocked on the lock: */ - task->blocked_on = waiter; + /* Current thread can't be already blocked (since it's executing!) */ + DEBUG_LOCKS_WARN_ON(get_task_blocked_on(task)); } void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *waiter, struct task_struct *task) { + struct mutex *blocked_on = get_task_blocked_on_once(task); + DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list)); DEBUG_LOCKS_WARN_ON(waiter->task != task); - DEBUG_LOCKS_WARN_ON(task->blocked_on != waiter); - task->blocked_on = NULL; + DEBUG_LOCKS_WARN_ON(blocked_on && blocked_on != lock); INIT_LIST_HEAD(&waiter->list); waiter->task = NULL; diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 543774506fdb..6084470773f6 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -592,6 +592,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas } raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); /* * After waiting to acquire the wait_lock, try again. */ @@ -622,6 +623,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas goto err_early_kill; } + set_task_blocked_on(current, lock); set_current_state(state); trace_contention_begin(lock, LCB_F_MUTEX); for (;;) { @@ -652,6 +654,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas goto err; } + raw_spin_unlock(¤t->blocked_lock); raw_spin_unlock_irqrestore(&lock->wait_lock, flags); /* Make sure we do wakeups before calling schedule */ if (!wake_q_empty(&wake_q)) { @@ -662,6 +665,13 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas first = __mutex_waiter_is_first(lock, &waiter); + raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); + + /* + * Re-set blocked_on_state as unlock path set it to WAKING/RUNNABLE + */ + current->blocked_on_state = BO_BLOCKED; set_current_state(state); /* * Here we order against unlock; we must either see it change @@ -672,16 +682,25 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas break; if (first) { + bool opt_acquired; + + /* + * mutex_optimistic_spin() can schedule, so we need to + * release these locks before calling it. + */ + raw_spin_unlock(¤t->blocked_lock); + raw_spin_unlock_irqrestore(&lock->wait_lock, flags); trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); - if (mutex_optimistic_spin(lock, ww_ctx, &waiter)) + opt_acquired = mutex_optimistic_spin(lock, ww_ctx, &waiter); + raw_spin_lock_irqsave(&lock->wait_lock, flags); + raw_spin_lock(¤t->blocked_lock); + if (opt_acquired) break; trace_contention_begin(lock, LCB_F_MUTEX); } - - raw_spin_lock_irqsave(&lock->wait_lock, flags); } - raw_spin_lock_irqsave(&lock->wait_lock, flags); acquired: + set_task_blocked_on(current, NULL); __set_current_state(TASK_RUNNING); if (ww_ctx) { @@ -706,16 +725,20 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas if (ww_ctx) ww_mutex_lock_acquired(ww, ww_ctx); + raw_spin_unlock(¤t->blocked_lock); raw_spin_unlock_irqrestore(&lock->wait_lock, flags); wake_up_q(&wake_q); preempt_enable(); return 0; err: + set_task_blocked_on(current, NULL); __set_current_state(TASK_RUNNING); __mutex_remove_waiter(lock, &waiter); err_early_kill: + WARN_ON(current->blocked_on); trace_contention_end(lock, ret); + raw_spin_unlock(¤t->blocked_lock); raw_spin_unlock_irqrestore(&lock->wait_lock, flags); debug_mutex_free_waiter(&waiter); mutex_release(&lock->dep_map, ip); @@ -925,8 +948,12 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne next = waiter->task; + raw_spin_lock(&next->blocked_lock); debug_mutex_wake_waiter(lock, waiter); + WARN_ON(next->blocked_on != lock); + next->blocked_on_state = BO_WAKING; wake_q_add(&wake_q, next); + raw_spin_unlock(&next->blocked_lock); } if (owner & MUTEX_FLAG_HANDOFF) diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h index 9facc0ddfdd3..8dd21ff5eee0 100644 --- a/kernel/locking/ww_mutex.h +++ b/kernel/locking/ww_mutex.h @@ -281,10 +281,21 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter, return false; if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)) { + /* nested as we should hold current->blocked_lock already */ + raw_spin_lock_nested(&waiter->task->blocked_lock, SINGLE_DEPTH_NESTING); #ifndef WW_RT debug_mutex_wake_waiter(lock, waiter); #endif + /* + * When waking up the task to die, be sure to set the + * blocked_on_state to WAKING. Otherwise we can see + * circular blocked_on relationships that can't + * resolve. + */ + WARN_ON(waiter->task->blocked_on != lock); + waiter->task->blocked_on_state = BO_WAKING; wake_q_add(wake_q, waiter->task); + raw_spin_unlock(&waiter->task->blocked_lock); } return true; @@ -331,9 +342,18 @@ static bool __ww_mutex_wound(struct MUTEX *lock, * it's wounded in __ww_mutex_check_kill() or has a * wakeup pending to re-read the wounded state. */ - if (owner != current) + if (owner != current) { + /* nested as we should hold current->blocked_lock already */ + raw_spin_lock_nested(&owner->blocked_lock, SINGLE_DEPTH_NESTING); + /* + * When waking up the task to wound, be sure to set the + * blocked_on_state flag. Otherwise we can see circular + * blocked_on relationships that can't resolve. + */ + owner->blocked_on_state = BO_WAKING; wake_q_add(wake_q, owner); - + raw_spin_unlock(&owner->blocked_lock); + } return true; } diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a708d225c28e..4e46189d545d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4195,6 +4195,7 @@ bool ttwu_state_match(struct task_struct *p, unsigned int state, int *success) int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) { guard(preempt)(); + unsigned long flags; int cpu, success = 0; if (p == current) { @@ -4341,6 +4342,11 @@ int try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) ttwu_queue(p, cpu, wake_flags); } + /* XXX can we do something better here for !CONFIG_SCHED_PROXY_EXEC case */ + raw_spin_lock_irqsave(&p->blocked_lock, flags); + if (p->blocked_on_state == BO_WAKING) + p->blocked_on_state = BO_RUNNABLE; + raw_spin_unlock_irqrestore(&p->blocked_lock, flags); out: if (success) ttwu_stat(p, task_cpu(p), wake_flags); -- 2.43.0.472.g3155946c3a-goog
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