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McKenney" , Metin Kaya , Xuewen Yan , K Prateek Nayak , Thomas Gleixner , Daniel Lezcano , Suleiman Souhlal , kernel-team@android.com, "Connor O'Brien" , John Stultz Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Valentin Schneider This lets us assert mutex::wait_lock is held whenever we access p->blocked_on, as well as warn us for unexpected state changes. Cc: Joel Fernandes Cc: Qais Yousef Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Valentin Schneider Cc: Steven Rostedt Cc: Ben Segall Cc: Zimuzo Ezeozue Cc: Mel Gorman Cc: Will Deacon Cc: Waiman Long Cc: Boqun Feng Cc: "Paul E. McKenney" Cc: Metin Kaya Cc: Xuewen Yan Cc: K Prateek Nayak Cc: Thomas Gleixner Cc: Daniel Lezcano Cc: Suleiman Souhlal Cc: kernel-team@android.com Signed-off-by: Valentin Schneider [fix conflicts, call in more places] Signed-off-by: Connor O'Brien [jstultz: tweaked commit subject, reworked a good bit] Signed-off-by: John Stultz --- v2: * Added get_task_blocked_on() accessor v4: * Address READ_ONCE usage that was dropped in v2 * Reordered to be a later add on to the main patch series as Peter was unhappy with similar wrappers in other patches. v5: * Added some extra correctness checking in wrappers v7: * Tweaks to reorder this change in the patch series * Minor cleanup to set_task_blocked_on() suggested by Metin Kaya v15: * Split out into its own patch again. * Further improve assumption checks in helpers. --- include/linux/sched.h | 44 ++++++++++++++++++++++++++++++++++-- kernel/locking/mutex-debug.c | 4 ++-- kernel/locking/mutex.c | 20 +++++----------- kernel/locking/ww_mutex.h | 6 ++--- 4 files changed, 52 insertions(+), 22 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 03775c44b7073..62870077379a6 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -34,6 +34,7 @@ #include #include #include +#include #include #include #include @@ -2154,6 +2155,47 @@ extern int __cond_resched_rwlock_write(rwlock_t *loc= k); __cond_resched_rwlock_write(lock); \ }) =20 +static inline void __set_task_blocked_on(struct task_struct *p, struct mut= ex *m) +{ + WARN_ON_ONCE(!m); + /* The task should only be setting itself as blocked */ + WARN_ON_ONCE(p !=3D current); + /* Currently we serialize blocked_on under the mutex::wait_lock */ + lockdep_assert_held_once(&m->wait_lock); + /* + * Check ensure we don't overwrite exisiting 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 !=3D m); + p->blocked_on =3D 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 m= utex *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 !=3D m); + p->blocked_on =3D NULL; +} + +static inline struct mutex *__get_task_blocked_on(struct task_struct *p) +{ + return READ_ONCE(p->blocked_on); +} + static __always_inline bool need_resched(void) { return unlikely(tif_need_resched()); @@ -2193,8 +2235,6 @@ 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); =20 -#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 758b7a6792b0c..949103fd8e9b5 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); =20 /* 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)); } =20 void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *wa= iter, struct task_struct *task) { - struct mutex *blocked_on =3D READ_ONCE(task->blocked_on); + struct mutex *blocked_on =3D __get_task_blocked_on(task); =20 DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list)); DEBUG_LOCKS_WARN_ON(waiter->task !=3D task); diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index 37d1966970617..351500cf50ece 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -627,8 +627,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas goto err_early_kill; } =20 - WARN_ON(current->blocked_on); - current->blocked_on =3D lock; + __set_task_blocked_on(current, lock); set_current_state(state); trace_contention_begin(lock, LCB_F_MUTEX); for (;;) { @@ -670,7 +669,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas * that has cleared our blocked_on state, re-set * it to the lock we are trying to aquire. */ - current->blocked_on =3D lock; + set_task_blocked_on(current, lock); set_current_state(state); /* * Here we order against unlock; we must either see it change @@ -691,7 +690,7 @@ __mutex_lock_common(struct mutex *lock, unsigned int st= ate, unsigned int subclas } raw_spin_lock_irqsave(&lock->wait_lock, flags); acquired: - current->blocked_on =3D NULL; + __clear_task_blocked_on(current, lock); __set_current_state(TASK_RUNNING); =20 if (ww_ctx) { @@ -721,11 +720,11 @@ __mutex_lock_common(struct mutex *lock, unsigned int = state, unsigned int subclas return 0; =20 err: - current->blocked_on =3D 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); @@ -935,14 +934,7 @@ static noinline void __sched __mutex_unlock_slowpath(s= truct mutex *lock, unsigne next =3D waiter->task; =20 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 !=3D lock); - next->blocked_on =3D NULL; + __clear_task_blocked_on(next, lock); wake_q_add(&wake_q, next); } =20 diff --git a/kernel/locking/ww_mutex.h b/kernel/locking/ww_mutex.h index 00db40946328e..086fd5487ca77 100644 --- a/kernel/locking/ww_mutex.h +++ b/kernel/locking/ww_mutex.h @@ -289,9 +289,7 @@ __ww_mutex_die(struct MUTEX *lock, struct MUTEX_WAITER = *waiter, * 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 !=3D lock); - waiter->task->blocked_on =3D NULL; + __clear_task_blocked_on(waiter->task, lock); wake_q_add(wake_q, waiter->task); } =20 @@ -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 =3D NULL; + __clear_task_blocked_on(owner, lock); wake_q_add(wake_q, owner); } return true; --=20 2.49.0.rc0.332.g42c0ae87b1-goog