From: Valentin Schneider Date: Sat, 12 Jul 2025 03:33:44 +0000 (+0000) Subject: locking/mutex: Add p->blocked_on wrappers for correctness checks X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=a4f0b6fef4b08e9928449206390133e48ac185a7;p=thirdparty%2Fkernel%2Fstable.git locking/mutex: Add p->blocked_on wrappers for correctness checks This lets us assert mutex::wait_lock is held whenever we access p->blocked_on, as well as warn us for unexpected state changes. [fix conflicts, call in more places] [jstultz: tweaked commit subject, reworked a good bit] Signed-off-by: Valentin Schneider Signed-off-by: Connor O'Brien Signed-off-by: John Stultz Signed-off-by: Peter Zijlstra (Intel) Tested-by: K Prateek Nayak Link: https://lkml.kernel.org/r/20250712033407.2383110-4-jstultz@google.com --- diff --git a/include/linux/sched.h b/include/linux/sched.h index 33ad240ec900..5b4e1cd52e27 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -34,6 +34,7 @@ #include #include #include +#include #include #include #include @@ -2129,6 +2130,67 @@ extern int __cond_resched_rwlock_write(rwlock_t *lock); __cond_resched_rwlock_write(lock); \ }) +#ifndef CONFIG_PREEMPT_RT +static inline struct mutex *__get_task_blocked_on(struct task_struct *p) +{ + struct mutex *m = p->blocked_on; + + if (m) + lockdep_assert_held_once(&m->wait_lock); + return m; +} + +static inline void __set_task_blocked_on(struct task_struct *p, struct mutex *m) +{ + WARN_ON_ONCE(!m); + /* The task should only be setting itself as blocked */ + WARN_ON_ONCE(p != current); + /* Currently we serialize blocked_on under the mutex::wait_lock */ + lockdep_assert_held_once(&m->wait_lock); + /* + * Check ensure we don't overwrite existing mutex value + * with a different mutex. Note, setting it to the same + * lock repeatedly is ok. + */ + WARN_ON_ONCE(p->blocked_on && p->blocked_on != m); + p->blocked_on = m; +} + +static inline void set_task_blocked_on(struct task_struct *p, struct mutex *m) +{ + guard(raw_spinlock_irqsave)(&m->wait_lock); + __set_task_blocked_on(p, m); +} + +static inline void __clear_task_blocked_on(struct task_struct *p, struct mutex *m) +{ + WARN_ON_ONCE(!m); + /* Currently we serialize blocked_on under the mutex::wait_lock */ + lockdep_assert_held_once(&m->wait_lock); + /* + * There may be cases where we re-clear already cleared + * blocked_on relationships, but make sure we are not + * clearing the relationship with a different lock. + */ + WARN_ON_ONCE(m && p->blocked_on && p->blocked_on != m); + p->blocked_on = NULL; +} + +static inline void clear_task_blocked_on(struct task_struct *p, struct mutex *m) +{ + guard(raw_spinlock_irqsave)(&m->wait_lock); + __clear_task_blocked_on(p, m); +} +#else +static inline void __clear_task_blocked_on(struct task_struct *p, struct rt_mutex *m) +{ +} + +static inline void clear_task_blocked_on(struct task_struct *p, struct rt_mutex *m) +{ +} +#endif /* !CONFIG_PREEMPT_RT */ + static __always_inline bool need_resched(void) { return unlikely(tif_need_resched()); @@ -2168,8 +2230,6 @@ extern bool sched_task_on_rq(struct task_struct *p); extern unsigned long get_wchan(struct task_struct *p); extern struct task_struct *cpu_curr_snapshot(int cpu); -#include - /* * In order to reduce various lock holder preemption latencies provide an * interface to see if a vCPU is currently running or not. diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c index 758b7a6792b0..949103fd8e9b 100644 --- a/kernel/locking/mutex-debug.c +++ b/kernel/locking/mutex-debug.c @@ -54,13 +54,13 @@ void debug_mutex_add_waiter(struct mutex *lock, struct mutex_waiter *waiter, lockdep_assert_held(&lock->wait_lock); /* Current thread can't be already blocked (since it's executing!) */ - DEBUG_LOCKS_WARN_ON(task->blocked_on); + 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 = READ_ONCE(task->blocked_on); + struct mutex *blocked_on = __get_task_blocked_on(task); DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list)); DEBUG_LOCKS_WARN_ON(waiter->task != task); diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index e2f59863a866..80d778fedd60 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -644,8 +644,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas goto err_early_kill; } - WARN_ON(current->blocked_on); - current->blocked_on = lock; + __set_task_blocked_on(current, lock); set_current_state(state); trace_contention_begin(lock, LCB_F_MUTEX); for (;;) { @@ -685,9 +684,9 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas /* * As we likely have been woken up by task * that has cleared our blocked_on state, re-set - * it to the lock we are trying to aquire. + * it to the lock we are trying to acquire. */ - current->blocked_on = lock; + set_task_blocked_on(current, lock); set_current_state(state); /* * Here we order against unlock; we must either see it change @@ -699,11 +698,15 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas if (first) { trace_contention_begin(lock, LCB_F_MUTEX | LCB_F_SPIN); - /* clear blocked_on as mutex_optimistic_spin may schedule() */ - current->blocked_on = NULL; + /* + * mutex_optimistic_spin() can call schedule(), so + * clear blocked on so we don't become unselectable + * to run. + */ + clear_task_blocked_on(current, lock); if (mutex_optimistic_spin(lock, ww_ctx, &waiter)) break; - current->blocked_on = lock; + set_task_blocked_on(current, lock); trace_contention_begin(lock, LCB_F_MUTEX); } @@ -711,7 +714,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas } raw_spin_lock_irqsave(&lock->wait_lock, flags); acquired: - current->blocked_on = NULL; + __clear_task_blocked_on(current, lock); __set_current_state(TASK_RUNNING); if (ww_ctx) { @@ -741,11 +744,11 @@ skip_wait: return 0; err: - current->blocked_on = NULL; + __clear_task_blocked_on(current, lock); __set_current_state(TASK_RUNNING); __mutex_remove_waiter(lock, &waiter); err_early_kill: - WARN_ON(current->blocked_on); + WARN_ON(__get_task_blocked_on(current)); trace_contention_end(lock, ret); raw_spin_unlock_irqrestore_wake(&lock->wait_lock, flags, &wake_q); debug_mutex_free_waiter(&waiter); @@ -956,14 +959,7 @@ static noinline void __sched __mutex_unlock_slowpath(struct mutex *lock, unsigne next = waiter->task; debug_mutex_wake_waiter(lock, waiter); - /* - * Unlock wakeups can be happening in parallel - * (when optimistic spinners steal and release - * the lock), so blocked_on may already be - * cleared here. - */ - WARN_ON(next->blocked_on && next->blocked_on != lock); - next->blocked_on = NULL; + __clear_task_blocked_on(next, lock); wake_q_add(&wake_q, next); } diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h index 45fe05e51db1..086fd5487ca7 100644 --- a/kernel/locking/ww_mutex.h +++ b/kernel/locking/ww_mutex.h @@ -283,15 +283,13 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER *waiter, if (waiter->ww_ctx->acquired > 0 && __ww_ctx_less(waiter->ww_ctx, ww_ctx)) { #ifndef WW_RT debug_mutex_wake_waiter(lock, waiter); +#endif /* * When waking up the task to die, be sure to clear the * blocked_on pointer. Otherwise we can see circular * blocked_on relationships that can't resolve. */ - WARN_ON(waiter->task->blocked_on && - waiter->task->blocked_on != lock); -#endif - waiter->task->blocked_on = NULL; + __clear_task_blocked_on(waiter->task, lock); wake_q_add(wake_q, waiter->task); } @@ -345,7 +343,7 @@ static bool __ww_mutex_wound(struct MUTEX *lock, * blocked_on pointer. Otherwise we can see circular * blocked_on relationships that can't resolve. */ - owner->blocked_on = NULL; + __clear_task_blocked_on(owner, lock); wake_q_add(wake_q, owner); } return true;