2 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
4 * started by Ingo Molnar and Thomas Gleixner.
6 * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
7 * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
8 * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
9 * Copyright (C) 2006 Esben Nielsen
11 * See Documentation/locking/rt-mutex-design.txt for details.
13 #include <linux/spinlock.h>
14 #include <linux/export.h>
15 #include <linux/sched.h>
16 #include <linux/sched/rt.h>
17 #include <linux/sched/deadline.h>
18 #include <linux/timer.h>
20 #include "rtmutex_common.h"
23 * lock->owner state tracking:
25 * lock->owner holds the task_struct pointer of the owner. Bit 0
26 * is used to keep track of the "lock has waiters" state.
29 * NULL 0 lock is free (fast acquire possible)
30 * NULL 1 lock is free and has waiters and the top waiter
31 * is going to take the lock*
32 * taskpointer 0 lock is held (fast release possible)
33 * taskpointer 1 lock is held and has waiters**
35 * The fast atomic compare exchange based acquire and release is only
36 * possible when bit 0 of lock->owner is 0.
38 * (*) It also can be a transitional state when grabbing the lock
39 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
40 * we need to set the bit0 before looking at the lock, and the owner may be
41 * NULL in this small time, hence this can be a transitional state.
43 * (**) There is a small time when bit 0 is set but there are no
44 * waiters. This can happen when grabbing the lock in the slow path.
45 * To prevent a cmpxchg of the owner releasing the lock, we need to
46 * set this bit before looking at the lock.
50 rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
52 unsigned long val = (unsigned long)owner;
54 if (rt_mutex_has_waiters(lock))
55 val |= RT_MUTEX_HAS_WAITERS;
57 lock->owner = (struct task_struct *)val;
60 static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
62 lock->owner = (struct task_struct *)
63 ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
66 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
68 unsigned long owner, *p = (unsigned long *) &lock->owner;
70 if (rt_mutex_has_waiters(lock))
74 * The rbtree has no waiters enqueued, now make sure that the
75 * lock->owner still has the waiters bit set, otherwise the
76 * following can happen:
82 * l->owner = T1 | HAS_WAITERS;
90 * l->owner = T1 | HAS_WAITERS;
95 * signal(->T2) signal(->T3)
102 * ==> wait list is empty
106 * fixup_rt_mutex_waiters()
107 * if (wait_list_empty(l) {
109 * owner = l->owner & ~HAS_WAITERS;
113 * rt_mutex_unlock(l) fixup_rt_mutex_waiters()
114 * if (wait_list_empty(l) {
115 * owner = l->owner & ~HAS_WAITERS;
116 * cmpxchg(l->owner, T1, NULL)
117 * ===> Success (l->owner = NULL)
123 * With the check for the waiter bit in place T3 on CPU2 will not
124 * overwrite. All tasks fiddling with the waiters bit are
125 * serialized by l->lock, so nothing else can modify the waiters
126 * bit. If the bit is set then nothing can change l->owner either
127 * so the simple RMW is safe. The cmpxchg() will simply fail if it
128 * happens in the middle of the RMW because the waiters bit is
131 owner = READ_ONCE(*p);
132 if (owner & RT_MUTEX_HAS_WAITERS)
133 WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
137 * We can speed up the acquire/release, if there's no debugging state to be
140 #ifndef CONFIG_DEBUG_RT_MUTEXES
141 # define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
142 # define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
143 # define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
146 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
147 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
148 * relaxed semantics suffice.
150 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
152 unsigned long owner, *p = (unsigned long *) &lock->owner;
156 } while (cmpxchg_relaxed(p, owner,
157 owner | RT_MUTEX_HAS_WAITERS) != owner);
161 * Safe fastpath aware unlock:
162 * 1) Clear the waiters bit
163 * 2) Drop lock->wait_lock
164 * 3) Try to unlock the lock with cmpxchg
166 static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
168 __releases(lock->wait_lock)
170 struct task_struct *owner = rt_mutex_owner(lock);
172 clear_rt_mutex_waiters(lock);
173 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
175 * If a new waiter comes in between the unlock and the cmpxchg
176 * we have two situations:
180 * cmpxchg(p, owner, 0) == owner
181 * mark_rt_mutex_waiters(lock);
187 * mark_rt_mutex_waiters(lock);
189 * cmpxchg(p, owner, 0) != owner
198 return rt_mutex_cmpxchg_release(lock, owner, NULL);
202 # define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
203 # define rt_mutex_cmpxchg_acquire(l,c,n) (0)
204 # define rt_mutex_cmpxchg_release(l,c,n) (0)
206 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
208 lock->owner = (struct task_struct *)
209 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
213 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
215 static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
217 __releases(lock->wait_lock)
220 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
226 rt_mutex_waiter_less(struct rt_mutex_waiter *left,
227 struct rt_mutex_waiter *right)
229 if (left->prio < right->prio)
233 * If both waiters have dl_prio(), we check the deadlines of the
235 * If left waiter has a dl_prio(), and we didn't return 1 above,
236 * then right waiter has a dl_prio() too.
238 if (dl_prio(left->prio))
239 return dl_time_before(left->task->dl.deadline,
240 right->task->dl.deadline);
246 rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
248 struct rb_node **link = &lock->waiters.rb_node;
249 struct rb_node *parent = NULL;
250 struct rt_mutex_waiter *entry;
255 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
256 if (rt_mutex_waiter_less(waiter, entry)) {
257 link = &parent->rb_left;
259 link = &parent->rb_right;
265 lock->waiters_leftmost = &waiter->tree_entry;
267 rb_link_node(&waiter->tree_entry, parent, link);
268 rb_insert_color(&waiter->tree_entry, &lock->waiters);
272 rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
274 if (RB_EMPTY_NODE(&waiter->tree_entry))
277 if (lock->waiters_leftmost == &waiter->tree_entry)
278 lock->waiters_leftmost = rb_next(&waiter->tree_entry);
280 rb_erase(&waiter->tree_entry, &lock->waiters);
281 RB_CLEAR_NODE(&waiter->tree_entry);
285 rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
287 struct rb_node **link = &task->pi_waiters.rb_node;
288 struct rb_node *parent = NULL;
289 struct rt_mutex_waiter *entry;
294 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
295 if (rt_mutex_waiter_less(waiter, entry)) {
296 link = &parent->rb_left;
298 link = &parent->rb_right;
304 task->pi_waiters_leftmost = &waiter->pi_tree_entry;
306 rb_link_node(&waiter->pi_tree_entry, parent, link);
307 rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
311 rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
313 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
316 if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
317 task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
319 rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
320 RB_CLEAR_NODE(&waiter->pi_tree_entry);
324 * Calculate task priority from the waiter tree priority
326 * Return task->normal_prio when the waiter tree is empty or when
327 * the waiter is not allowed to do priority boosting
329 int rt_mutex_getprio(struct task_struct *task)
331 if (likely(!task_has_pi_waiters(task)))
332 return task->normal_prio;
334 return min(task_top_pi_waiter(task)->prio,
338 struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
340 if (likely(!task_has_pi_waiters(task)))
343 return task_top_pi_waiter(task)->task;
347 * Called by sched_setscheduler() to get the priority which will be
348 * effective after the change.
350 int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
352 if (!task_has_pi_waiters(task))
355 if (task_top_pi_waiter(task)->task->prio <= newprio)
356 return task_top_pi_waiter(task)->task->prio;
361 * Adjust the priority of a task, after its pi_waiters got modified.
363 * This can be both boosting and unboosting. task->pi_lock must be held.
365 static void __rt_mutex_adjust_prio(struct task_struct *task)
367 int prio = rt_mutex_getprio(task);
369 if (task->prio != prio || dl_prio(prio))
370 rt_mutex_setprio(task, prio);
374 * Adjust task priority (undo boosting). Called from the exit path of
375 * rt_mutex_slowunlock() and rt_mutex_slowlock().
377 * (Note: We do this outside of the protection of lock->wait_lock to
378 * allow the lock to be taken while or before we readjust the priority
379 * of task. We do not use the spin_xx_mutex() variants here as we are
380 * outside of the debug path.)
382 void rt_mutex_adjust_prio(struct task_struct *task)
386 raw_spin_lock_irqsave(&task->pi_lock, flags);
387 __rt_mutex_adjust_prio(task);
388 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
392 * Deadlock detection is conditional:
394 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
395 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
397 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
398 * conducted independent of the detect argument.
400 * If the waiter argument is NULL this indicates the deboost path and
401 * deadlock detection is disabled independent of the detect argument
402 * and the config settings.
404 static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
405 enum rtmutex_chainwalk chwalk)
408 * This is just a wrapper function for the following call,
409 * because debug_rt_mutex_detect_deadlock() smells like a magic
410 * debug feature and I wanted to keep the cond function in the
411 * main source file along with the comments instead of having
412 * two of the same in the headers.
414 return debug_rt_mutex_detect_deadlock(waiter, chwalk);
418 * Max number of times we'll walk the boosting chain:
420 int max_lock_depth = 1024;
422 static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
424 return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
428 * Adjust the priority chain. Also used for deadlock detection.
429 * Decreases task's usage by one - may thus free the task.
431 * @task: the task owning the mutex (owner) for which a chain walk is
433 * @chwalk: do we have to carry out deadlock detection?
434 * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
435 * things for a task that has just got its priority adjusted, and
436 * is waiting on a mutex)
437 * @next_lock: the mutex on which the owner of @orig_lock was blocked before
438 * we dropped its pi_lock. Is never dereferenced, only used for
439 * comparison to detect lock chain changes.
440 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
441 * its priority to the mutex owner (can be NULL in the case
442 * depicted above or if the top waiter is gone away and we are
443 * actually deboosting the owner)
444 * @top_task: the current top waiter
446 * Returns 0 or -EDEADLK.
448 * Chain walk basics and protection scope
450 * [R] refcount on task
451 * [P] task->pi_lock held
452 * [L] rtmutex->wait_lock held
454 * Step Description Protected by
455 * function arguments:
457 * @orig_lock if != NULL @top_task is blocked on it
458 * @next_lock Unprotected. Cannot be
459 * dereferenced. Only used for
461 * @orig_waiter if != NULL @top_task is blocked on it
462 * @top_task current, or in case of proxy
463 * locking protected by calling
466 * loop_sanity_check();
468 * [1] lock(task->pi_lock); [R] acquire [P]
469 * [2] waiter = task->pi_blocked_on; [P]
470 * [3] check_exit_conditions_1(); [P]
471 * [4] lock = waiter->lock; [P]
472 * [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
473 * unlock(task->pi_lock); release [P]
476 * [6] check_exit_conditions_2(); [P] + [L]
477 * [7] requeue_lock_waiter(lock, waiter); [P] + [L]
478 * [8] unlock(task->pi_lock); release [P]
479 * put_task_struct(task); release [R]
480 * [9] check_exit_conditions_3(); [L]
481 * [10] task = owner(lock); [L]
482 * get_task_struct(task); [L] acquire [R]
483 * lock(task->pi_lock); [L] acquire [P]
484 * [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
485 * [12] check_exit_conditions_4(); [P] + [L]
486 * [13] unlock(task->pi_lock); release [P]
487 * unlock(lock->wait_lock); release [L]
490 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
491 enum rtmutex_chainwalk chwalk,
492 struct rt_mutex *orig_lock,
493 struct rt_mutex *next_lock,
494 struct rt_mutex_waiter *orig_waiter,
495 struct task_struct *top_task)
497 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
498 struct rt_mutex_waiter *prerequeue_top_waiter;
499 int ret = 0, depth = 0;
500 struct rt_mutex *lock;
501 bool detect_deadlock;
504 detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
507 * The (de)boosting is a step by step approach with a lot of
508 * pitfalls. We want this to be preemptible and we want hold a
509 * maximum of two locks per step. So we have to check
510 * carefully whether things change under us.
514 * We limit the lock chain length for each invocation.
516 if (++depth > max_lock_depth) {
520 * Print this only once. If the admin changes the limit,
521 * print a new message when reaching the limit again.
523 if (prev_max != max_lock_depth) {
524 prev_max = max_lock_depth;
525 printk(KERN_WARNING "Maximum lock depth %d reached "
526 "task: %s (%d)\n", max_lock_depth,
527 top_task->comm, task_pid_nr(top_task));
529 put_task_struct(task);
535 * We are fully preemptible here and only hold the refcount on
536 * @task. So everything can have changed under us since the
537 * caller or our own code below (goto retry/again) dropped all
542 * [1] Task cannot go away as we did a get_task() before !
544 raw_spin_lock_irq(&task->pi_lock);
547 * [2] Get the waiter on which @task is blocked on.
549 waiter = task->pi_blocked_on;
552 * [3] check_exit_conditions_1() protected by task->pi_lock.
556 * Check whether the end of the boosting chain has been
557 * reached or the state of the chain has changed while we
564 * Check the orig_waiter state. After we dropped the locks,
565 * the previous owner of the lock might have released the lock.
567 if (orig_waiter && !rt_mutex_owner(orig_lock))
571 * We dropped all locks after taking a refcount on @task, so
572 * the task might have moved on in the lock chain or even left
573 * the chain completely and blocks now on an unrelated lock or
576 * We stored the lock on which @task was blocked in @next_lock,
577 * so we can detect the chain change.
579 if (next_lock != waiter->lock)
583 * Drop out, when the task has no waiters. Note,
584 * top_waiter can be NULL, when we are in the deboosting
588 if (!task_has_pi_waiters(task))
591 * If deadlock detection is off, we stop here if we
592 * are not the top pi waiter of the task. If deadlock
593 * detection is enabled we continue, but stop the
594 * requeueing in the chain walk.
596 if (top_waiter != task_top_pi_waiter(task)) {
597 if (!detect_deadlock)
605 * If the waiter priority is the same as the task priority
606 * then there is no further priority adjustment necessary. If
607 * deadlock detection is off, we stop the chain walk. If its
608 * enabled we continue, but stop the requeueing in the chain
611 if (waiter->prio == task->prio) {
612 if (!detect_deadlock)
619 * [4] Get the next lock
623 * [5] We need to trylock here as we are holding task->pi_lock,
624 * which is the reverse lock order versus the other rtmutex
627 if (!raw_spin_trylock(&lock->wait_lock)) {
628 raw_spin_unlock_irq(&task->pi_lock);
634 * [6] check_exit_conditions_2() protected by task->pi_lock and
637 * Deadlock detection. If the lock is the same as the original
638 * lock which caused us to walk the lock chain or if the
639 * current lock is owned by the task which initiated the chain
640 * walk, we detected a deadlock.
642 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
643 debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
644 raw_spin_unlock(&lock->wait_lock);
650 * If we just follow the lock chain for deadlock detection, no
651 * need to do all the requeue operations. To avoid a truckload
652 * of conditionals around the various places below, just do the
653 * minimum chain walk checks.
657 * No requeue[7] here. Just release @task [8]
659 raw_spin_unlock(&task->pi_lock);
660 put_task_struct(task);
663 * [9] check_exit_conditions_3 protected by lock->wait_lock.
664 * If there is no owner of the lock, end of chain.
666 if (!rt_mutex_owner(lock)) {
667 raw_spin_unlock_irq(&lock->wait_lock);
671 /* [10] Grab the next task, i.e. owner of @lock */
672 task = rt_mutex_owner(lock);
673 get_task_struct(task);
674 raw_spin_lock(&task->pi_lock);
677 * No requeue [11] here. We just do deadlock detection.
679 * [12] Store whether owner is blocked
680 * itself. Decision is made after dropping the locks
682 next_lock = task_blocked_on_lock(task);
684 * Get the top waiter for the next iteration
686 top_waiter = rt_mutex_top_waiter(lock);
688 /* [13] Drop locks */
689 raw_spin_unlock(&task->pi_lock);
690 raw_spin_unlock_irq(&lock->wait_lock);
692 /* If owner is not blocked, end of chain. */
699 * Store the current top waiter before doing the requeue
700 * operation on @lock. We need it for the boost/deboost
703 prerequeue_top_waiter = rt_mutex_top_waiter(lock);
705 /* [7] Requeue the waiter in the lock waiter tree. */
706 rt_mutex_dequeue(lock, waiter);
707 waiter->prio = task->prio;
708 rt_mutex_enqueue(lock, waiter);
710 /* [8] Release the task */
711 raw_spin_unlock(&task->pi_lock);
712 put_task_struct(task);
715 * [9] check_exit_conditions_3 protected by lock->wait_lock.
717 * We must abort the chain walk if there is no lock owner even
718 * in the dead lock detection case, as we have nothing to
719 * follow here. This is the end of the chain we are walking.
721 if (!rt_mutex_owner(lock)) {
723 * If the requeue [7] above changed the top waiter,
724 * then we need to wake the new top waiter up to try
727 if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
728 wake_up_process(rt_mutex_top_waiter(lock)->task);
729 raw_spin_unlock_irq(&lock->wait_lock);
733 /* [10] Grab the next task, i.e. the owner of @lock */
734 task = rt_mutex_owner(lock);
735 get_task_struct(task);
736 raw_spin_lock(&task->pi_lock);
738 /* [11] requeue the pi waiters if necessary */
739 if (waiter == rt_mutex_top_waiter(lock)) {
741 * The waiter became the new top (highest priority)
742 * waiter on the lock. Replace the previous top waiter
743 * in the owner tasks pi waiters tree with this waiter
744 * and adjust the priority of the owner.
746 rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
747 rt_mutex_enqueue_pi(task, waiter);
748 __rt_mutex_adjust_prio(task);
750 } else if (prerequeue_top_waiter == waiter) {
752 * The waiter was the top waiter on the lock, but is
753 * no longer the top prority waiter. Replace waiter in
754 * the owner tasks pi waiters tree with the new top
755 * (highest priority) waiter and adjust the priority
757 * The new top waiter is stored in @waiter so that
758 * @waiter == @top_waiter evaluates to true below and
759 * we continue to deboost the rest of the chain.
761 rt_mutex_dequeue_pi(task, waiter);
762 waiter = rt_mutex_top_waiter(lock);
763 rt_mutex_enqueue_pi(task, waiter);
764 __rt_mutex_adjust_prio(task);
767 * Nothing changed. No need to do any priority
773 * [12] check_exit_conditions_4() protected by task->pi_lock
774 * and lock->wait_lock. The actual decisions are made after we
777 * Check whether the task which owns the current lock is pi
778 * blocked itself. If yes we store a pointer to the lock for
779 * the lock chain change detection above. After we dropped
780 * task->pi_lock next_lock cannot be dereferenced anymore.
782 next_lock = task_blocked_on_lock(task);
784 * Store the top waiter of @lock for the end of chain walk
787 top_waiter = rt_mutex_top_waiter(lock);
789 /* [13] Drop the locks */
790 raw_spin_unlock(&task->pi_lock);
791 raw_spin_unlock_irq(&lock->wait_lock);
794 * Make the actual exit decisions [12], based on the stored
797 * We reached the end of the lock chain. Stop right here. No
798 * point to go back just to figure that out.
804 * If the current waiter is not the top waiter on the lock,
805 * then we can stop the chain walk here if we are not in full
806 * deadlock detection mode.
808 if (!detect_deadlock && waiter != top_waiter)
814 raw_spin_unlock_irq(&task->pi_lock);
816 put_task_struct(task);
822 * Try to take an rt-mutex
824 * Must be called with lock->wait_lock held and interrupts disabled
826 * @lock: The lock to be acquired.
827 * @task: The task which wants to acquire the lock
828 * @waiter: The waiter that is queued to the lock's wait tree if the
829 * callsite called task_blocked_on_lock(), otherwise NULL
831 static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
832 struct rt_mutex_waiter *waiter)
835 * Before testing whether we can acquire @lock, we set the
836 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
837 * other tasks which try to modify @lock into the slow path
838 * and they serialize on @lock->wait_lock.
840 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
841 * as explained at the top of this file if and only if:
843 * - There is a lock owner. The caller must fixup the
844 * transient state if it does a trylock or leaves the lock
845 * function due to a signal or timeout.
847 * - @task acquires the lock and there are no other
848 * waiters. This is undone in rt_mutex_set_owner(@task) at
849 * the end of this function.
851 mark_rt_mutex_waiters(lock);
854 * If @lock has an owner, give up.
856 if (rt_mutex_owner(lock))
860 * If @waiter != NULL, @task has already enqueued the waiter
861 * into @lock waiter tree. If @waiter == NULL then this is a
866 * If waiter is not the highest priority waiter of
869 if (waiter != rt_mutex_top_waiter(lock))
873 * We can acquire the lock. Remove the waiter from the
876 rt_mutex_dequeue(lock, waiter);
880 * If the lock has waiters already we check whether @task is
881 * eligible to take over the lock.
883 * If there are no other waiters, @task can acquire
884 * the lock. @task->pi_blocked_on is NULL, so it does
885 * not need to be dequeued.
887 if (rt_mutex_has_waiters(lock)) {
889 * If @task->prio is greater than or equal to
890 * the top waiter priority (kernel view),
893 if (task->prio >= rt_mutex_top_waiter(lock)->prio)
897 * The current top waiter stays enqueued. We
898 * don't have to change anything in the lock
903 * No waiters. Take the lock without the
904 * pi_lock dance.@task->pi_blocked_on is NULL
905 * and we have no waiters to enqueue in @task
913 * Clear @task->pi_blocked_on. Requires protection by
914 * @task->pi_lock. Redundant operation for the @waiter == NULL
915 * case, but conditionals are more expensive than a redundant
918 raw_spin_lock(&task->pi_lock);
919 task->pi_blocked_on = NULL;
921 * Finish the lock acquisition. @task is the new owner. If
922 * other waiters exist we have to insert the highest priority
923 * waiter into @task->pi_waiters tree.
925 if (rt_mutex_has_waiters(lock))
926 rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
927 raw_spin_unlock(&task->pi_lock);
930 /* We got the lock. */
931 debug_rt_mutex_lock(lock);
934 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
935 * are still waiters or clears it.
937 rt_mutex_set_owner(lock, task);
943 * Task blocks on lock.
945 * Prepare waiter and propagate pi chain
947 * This must be called with lock->wait_lock held and interrupts disabled
949 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
950 struct rt_mutex_waiter *waiter,
951 struct task_struct *task,
952 enum rtmutex_chainwalk chwalk)
954 struct task_struct *owner = rt_mutex_owner(lock);
955 struct rt_mutex_waiter *top_waiter = waiter;
956 struct rt_mutex *next_lock;
957 int chain_walk = 0, res;
960 * Early deadlock detection. We really don't want the task to
961 * enqueue on itself just to untangle the mess later. It's not
962 * only an optimization. We drop the locks, so another waiter
963 * can come in before the chain walk detects the deadlock. So
964 * the other will detect the deadlock and return -EDEADLOCK,
965 * which is wrong, as the other waiter is not in a deadlock
971 raw_spin_lock(&task->pi_lock);
972 __rt_mutex_adjust_prio(task);
975 waiter->prio = task->prio;
977 /* Get the top priority waiter on the lock */
978 if (rt_mutex_has_waiters(lock))
979 top_waiter = rt_mutex_top_waiter(lock);
980 rt_mutex_enqueue(lock, waiter);
982 task->pi_blocked_on = waiter;
984 raw_spin_unlock(&task->pi_lock);
989 raw_spin_lock(&owner->pi_lock);
990 if (waiter == rt_mutex_top_waiter(lock)) {
991 rt_mutex_dequeue_pi(owner, top_waiter);
992 rt_mutex_enqueue_pi(owner, waiter);
994 __rt_mutex_adjust_prio(owner);
995 if (owner->pi_blocked_on)
997 } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
1001 /* Store the lock on which owner is blocked or NULL */
1002 next_lock = task_blocked_on_lock(owner);
1004 raw_spin_unlock(&owner->pi_lock);
1006 * Even if full deadlock detection is on, if the owner is not
1007 * blocked itself, we can avoid finding this out in the chain
1010 if (!chain_walk || !next_lock)
1014 * The owner can't disappear while holding a lock,
1015 * so the owner struct is protected by wait_lock.
1016 * Gets dropped in rt_mutex_adjust_prio_chain()!
1018 get_task_struct(owner);
1020 raw_spin_unlock_irq(&lock->wait_lock);
1022 res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1023 next_lock, waiter, task);
1025 raw_spin_lock_irq(&lock->wait_lock);
1031 * Remove the top waiter from the current tasks pi waiter tree and
1034 * Called with lock->wait_lock held and interrupts disabled.
1036 static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
1037 struct rt_mutex *lock)
1039 struct rt_mutex_waiter *waiter;
1041 raw_spin_lock(¤t->pi_lock);
1043 waiter = rt_mutex_top_waiter(lock);
1046 * Remove it from current->pi_waiters. We do not adjust a
1047 * possible priority boost right now. We execute wakeup in the
1048 * boosted mode and go back to normal after releasing
1051 rt_mutex_dequeue_pi(current, waiter);
1054 * As we are waking up the top waiter, and the waiter stays
1055 * queued on the lock until it gets the lock, this lock
1056 * obviously has waiters. Just set the bit here and this has
1057 * the added benefit of forcing all new tasks into the
1058 * slow path making sure no task of lower priority than
1059 * the top waiter can steal this lock.
1061 lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1063 raw_spin_unlock(¤t->pi_lock);
1065 wake_q_add(wake_q, waiter->task);
1069 * Remove a waiter from a lock and give up
1071 * Must be called with lock->wait_lock held and interrupts disabled. I must
1072 * have just failed to try_to_take_rt_mutex().
1074 static void remove_waiter(struct rt_mutex *lock,
1075 struct rt_mutex_waiter *waiter)
1077 bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1078 struct task_struct *owner = rt_mutex_owner(lock);
1079 struct rt_mutex *next_lock;
1081 raw_spin_lock(¤t->pi_lock);
1082 rt_mutex_dequeue(lock, waiter);
1083 current->pi_blocked_on = NULL;
1084 raw_spin_unlock(¤t->pi_lock);
1087 * Only update priority if the waiter was the highest priority
1088 * waiter of the lock and there is an owner to update.
1090 if (!owner || !is_top_waiter)
1093 raw_spin_lock(&owner->pi_lock);
1095 rt_mutex_dequeue_pi(owner, waiter);
1097 if (rt_mutex_has_waiters(lock))
1098 rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1100 __rt_mutex_adjust_prio(owner);
1102 /* Store the lock on which owner is blocked or NULL */
1103 next_lock = task_blocked_on_lock(owner);
1105 raw_spin_unlock(&owner->pi_lock);
1108 * Don't walk the chain, if the owner task is not blocked
1114 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1115 get_task_struct(owner);
1117 raw_spin_unlock_irq(&lock->wait_lock);
1119 rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1120 next_lock, NULL, current);
1122 raw_spin_lock_irq(&lock->wait_lock);
1126 * Recheck the pi chain, in case we got a priority setting
1128 * Called from sched_setscheduler
1130 void rt_mutex_adjust_pi(struct task_struct *task)
1132 struct rt_mutex_waiter *waiter;
1133 struct rt_mutex *next_lock;
1134 unsigned long flags;
1136 raw_spin_lock_irqsave(&task->pi_lock, flags);
1138 waiter = task->pi_blocked_on;
1139 if (!waiter || (waiter->prio == task->prio &&
1140 !dl_prio(task->prio))) {
1141 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1144 next_lock = waiter->lock;
1145 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1147 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1148 get_task_struct(task);
1150 rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1151 next_lock, NULL, task);
1154 void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
1156 debug_rt_mutex_init_waiter(waiter);
1157 RB_CLEAR_NODE(&waiter->pi_tree_entry);
1158 RB_CLEAR_NODE(&waiter->tree_entry);
1159 waiter->task = NULL;
1163 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
1164 * @lock: the rt_mutex to take
1165 * @state: the state the task should block in (TASK_INTERRUPTIBLE
1166 * or TASK_UNINTERRUPTIBLE)
1167 * @timeout: the pre-initialized and started timer, or NULL for none
1168 * @waiter: the pre-initialized rt_mutex_waiter
1170 * Must be called with lock->wait_lock held and interrupts disabled
1173 __rt_mutex_slowlock(struct rt_mutex *lock, int state,
1174 struct hrtimer_sleeper *timeout,
1175 struct rt_mutex_waiter *waiter)
1180 /* Try to acquire the lock: */
1181 if (try_to_take_rt_mutex(lock, current, waiter))
1185 * TASK_INTERRUPTIBLE checks for signals and
1186 * timeout. Ignored otherwise.
1188 if (unlikely(state == TASK_INTERRUPTIBLE)) {
1189 /* Signal pending? */
1190 if (signal_pending(current))
1192 if (timeout && !timeout->task)
1198 raw_spin_unlock_irq(&lock->wait_lock);
1200 debug_rt_mutex_print_deadlock(waiter);
1204 raw_spin_lock_irq(&lock->wait_lock);
1205 set_current_state(state);
1208 __set_current_state(TASK_RUNNING);
1212 static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
1213 struct rt_mutex_waiter *w)
1216 * If the result is not -EDEADLOCK or the caller requested
1217 * deadlock detection, nothing to do here.
1219 if (res != -EDEADLOCK || detect_deadlock)
1223 * Yell lowdly and stop the task right here.
1225 rt_mutex_print_deadlock(w);
1227 set_current_state(TASK_INTERRUPTIBLE);
1233 * Slow path lock function:
1236 rt_mutex_slowlock(struct rt_mutex *lock, int state,
1237 struct hrtimer_sleeper *timeout,
1238 enum rtmutex_chainwalk chwalk)
1240 struct rt_mutex_waiter waiter;
1241 unsigned long flags;
1244 rt_mutex_init_waiter(&waiter);
1247 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1248 * be called in early boot if the cmpxchg() fast path is disabled
1249 * (debug, no architecture support). In this case we will acquire the
1250 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1251 * enable interrupts in that early boot case. So we need to use the
1252 * irqsave/restore variants.
1254 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1256 /* Try to acquire the lock again: */
1257 if (try_to_take_rt_mutex(lock, current, NULL)) {
1258 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1262 set_current_state(state);
1264 /* Setup the timer, when timeout != NULL */
1265 if (unlikely(timeout))
1266 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1268 ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1271 /* sleep on the mutex */
1272 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1274 if (unlikely(ret)) {
1275 __set_current_state(TASK_RUNNING);
1276 if (rt_mutex_has_waiters(lock))
1277 remove_waiter(lock, &waiter);
1278 rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1282 * try_to_take_rt_mutex() sets the waiter bit
1283 * unconditionally. We might have to fix that up.
1285 fixup_rt_mutex_waiters(lock);
1287 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1289 /* Remove pending timer: */
1290 if (unlikely(timeout))
1291 hrtimer_cancel(&timeout->timer);
1293 debug_rt_mutex_free_waiter(&waiter);
1298 static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
1300 int ret = try_to_take_rt_mutex(lock, current, NULL);
1303 * try_to_take_rt_mutex() sets the lock waiters bit
1304 * unconditionally. Clean this up.
1306 fixup_rt_mutex_waiters(lock);
1312 * Slow path try-lock function:
1314 static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1316 unsigned long flags;
1320 * If the lock already has an owner we fail to get the lock.
1321 * This can be done without taking the @lock->wait_lock as
1322 * it is only being read, and this is a trylock anyway.
1324 if (rt_mutex_owner(lock))
1328 * The mutex has currently no owner. Lock the wait lock and try to
1329 * acquire the lock. We use irqsave here to support early boot calls.
1331 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1333 ret = __rt_mutex_slowtrylock(lock);
1335 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1341 * Slow path to release a rt-mutex.
1342 * Return whether the current task needs to undo a potential priority boosting.
1344 static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1345 struct wake_q_head *wake_q)
1347 unsigned long flags;
1349 /* irqsave required to support early boot calls */
1350 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1352 debug_rt_mutex_unlock(lock);
1355 * We must be careful here if the fast path is enabled. If we
1356 * have no waiters queued we cannot set owner to NULL here
1359 * foo->lock->owner = NULL;
1360 * rtmutex_lock(foo->lock); <- fast path
1361 * free = atomic_dec_and_test(foo->refcnt);
1362 * rtmutex_unlock(foo->lock); <- fast path
1365 * raw_spin_unlock(foo->lock->wait_lock);
1367 * So for the fastpath enabled kernel:
1369 * Nothing can set the waiters bit as long as we hold
1370 * lock->wait_lock. So we do the following sequence:
1372 * owner = rt_mutex_owner(lock);
1373 * clear_rt_mutex_waiters(lock);
1374 * raw_spin_unlock(&lock->wait_lock);
1375 * if (cmpxchg(&lock->owner, owner, 0) == owner)
1379 * The fastpath disabled variant is simple as all access to
1380 * lock->owner is serialized by lock->wait_lock:
1382 * lock->owner = NULL;
1383 * raw_spin_unlock(&lock->wait_lock);
1385 while (!rt_mutex_has_waiters(lock)) {
1386 /* Drops lock->wait_lock ! */
1387 if (unlock_rt_mutex_safe(lock, flags) == true)
1389 /* Relock the rtmutex and try again */
1390 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1394 * The wakeup next waiter path does not suffer from the above
1395 * race. See the comments there.
1397 * Queue the next waiter for wakeup once we release the wait_lock.
1399 mark_wakeup_next_waiter(wake_q, lock);
1401 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1403 /* check PI boosting */
1408 * debug aware fast / slowpath lock,trylock,unlock
1410 * The atomic acquire/release ops are compiled away, when either the
1411 * architecture does not support cmpxchg or when debugging is enabled.
1414 rt_mutex_fastlock(struct rt_mutex *lock, int state,
1415 int (*slowfn)(struct rt_mutex *lock, int state,
1416 struct hrtimer_sleeper *timeout,
1417 enum rtmutex_chainwalk chwalk))
1419 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1422 return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1426 rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1427 struct hrtimer_sleeper *timeout,
1428 enum rtmutex_chainwalk chwalk,
1429 int (*slowfn)(struct rt_mutex *lock, int state,
1430 struct hrtimer_sleeper *timeout,
1431 enum rtmutex_chainwalk chwalk))
1433 if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1434 likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1437 return slowfn(lock, state, timeout, chwalk);
1441 rt_mutex_fasttrylock(struct rt_mutex *lock,
1442 int (*slowfn)(struct rt_mutex *lock))
1444 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1447 return slowfn(lock);
1451 rt_mutex_fastunlock(struct rt_mutex *lock,
1452 bool (*slowfn)(struct rt_mutex *lock,
1453 struct wake_q_head *wqh))
1458 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1461 deboost = slowfn(lock, &wake_q);
1465 /* Undo pi boosting if necessary: */
1467 rt_mutex_adjust_prio(current);
1471 * rt_mutex_lock - lock a rt_mutex
1473 * @lock: the rt_mutex to be locked
1475 void __sched rt_mutex_lock(struct rt_mutex *lock)
1479 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1481 EXPORT_SYMBOL_GPL(rt_mutex_lock);
1484 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1486 * @lock: the rt_mutex to be locked
1490 * -EINTR when interrupted by a signal
1492 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1496 return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1498 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1501 * Futex variant, must not use fastpath.
1503 int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
1505 return rt_mutex_slowtrylock(lock);
1508 int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
1510 return __rt_mutex_slowtrylock(lock);
1514 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1515 * the timeout structure is provided
1518 * @lock: the rt_mutex to be locked
1519 * @timeout: timeout structure or NULL (no timeout)
1523 * -EINTR when interrupted by a signal
1524 * -ETIMEDOUT when the timeout expired
1527 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1531 return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1532 RT_MUTEX_MIN_CHAINWALK,
1535 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1538 * rt_mutex_trylock - try to lock a rt_mutex
1540 * @lock: the rt_mutex to be locked
1542 * This function can only be called in thread context. It's safe to
1543 * call it from atomic regions, but not from hard interrupt or soft
1544 * interrupt context.
1546 * Returns 1 on success and 0 on contention
1548 int __sched rt_mutex_trylock(struct rt_mutex *lock)
1550 if (WARN_ON(in_irq() || in_nmi() || in_serving_softirq()))
1553 return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1555 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1558 * rt_mutex_unlock - unlock a rt_mutex
1560 * @lock: the rt_mutex to be unlocked
1562 void __sched rt_mutex_unlock(struct rt_mutex *lock)
1564 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1566 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1569 * Futex variant, that since futex variants do not use the fast-path, can be
1570 * simple and will not need to retry.
1572 bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
1573 struct wake_q_head *wake_q)
1575 lockdep_assert_held(&lock->wait_lock);
1577 debug_rt_mutex_unlock(lock);
1579 if (!rt_mutex_has_waiters(lock)) {
1581 return false; /* done */
1584 mark_wakeup_next_waiter(wake_q, lock);
1585 return true; /* deboost and wakeups */
1588 void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
1593 raw_spin_lock_irq(&lock->wait_lock);
1594 deboost = __rt_mutex_futex_unlock(lock, &wake_q);
1595 raw_spin_unlock_irq(&lock->wait_lock);
1599 rt_mutex_adjust_prio(current);
1604 * rt_mutex_destroy - mark a mutex unusable
1605 * @lock: the mutex to be destroyed
1607 * This function marks the mutex uninitialized, and any subsequent
1608 * use of the mutex is forbidden. The mutex must not be locked when
1609 * this function is called.
1611 void rt_mutex_destroy(struct rt_mutex *lock)
1613 WARN_ON(rt_mutex_is_locked(lock));
1614 #ifdef CONFIG_DEBUG_RT_MUTEXES
1619 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1622 * __rt_mutex_init - initialize the rt lock
1624 * @lock: the rt lock to be initialized
1626 * Initialize the rt lock to unlocked state.
1628 * Initializing of a locked rt lock is not allowed
1630 void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1633 raw_spin_lock_init(&lock->wait_lock);
1634 lock->waiters = RB_ROOT;
1635 lock->waiters_leftmost = NULL;
1637 debug_rt_mutex_init(lock, name);
1639 EXPORT_SYMBOL_GPL(__rt_mutex_init);
1642 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1645 * @lock: the rt_mutex to be locked
1646 * @proxy_owner:the task to set as owner
1648 * No locking. Caller has to do serializing itself
1649 * Special API call for PI-futex support
1651 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1652 struct task_struct *proxy_owner)
1654 __rt_mutex_init(lock, NULL);
1655 debug_rt_mutex_proxy_lock(lock, proxy_owner);
1656 rt_mutex_set_owner(lock, proxy_owner);
1660 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1662 * @lock: the rt_mutex to be locked
1664 * No locking. Caller has to do serializing itself
1665 * Special API call for PI-futex support
1667 void rt_mutex_proxy_unlock(struct rt_mutex *lock)
1669 debug_rt_mutex_proxy_unlock(lock);
1670 rt_mutex_set_owner(lock, NULL);
1674 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1675 * @lock: the rt_mutex to take
1676 * @waiter: the pre-initialized rt_mutex_waiter
1677 * @task: the task to prepare
1680 * 0 - task blocked on lock
1681 * 1 - acquired the lock for task, caller should wake it up
1684 * Special API call for FUTEX_REQUEUE_PI support.
1686 int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1687 struct rt_mutex_waiter *waiter,
1688 struct task_struct *task)
1692 raw_spin_lock_irq(&lock->wait_lock);
1694 if (try_to_take_rt_mutex(lock, task, NULL)) {
1695 raw_spin_unlock_irq(&lock->wait_lock);
1699 /* We enforce deadlock detection for futexes */
1700 ret = task_blocks_on_rt_mutex(lock, waiter, task,
1701 RT_MUTEX_FULL_CHAINWALK);
1703 if (ret && !rt_mutex_owner(lock)) {
1705 * Reset the return value. We might have
1706 * returned with -EDEADLK and the owner
1707 * released the lock while we were walking the
1708 * pi chain. Let the waiter sort it out.
1714 remove_waiter(lock, waiter);
1716 raw_spin_unlock_irq(&lock->wait_lock);
1718 debug_rt_mutex_print_deadlock(waiter);
1724 * rt_mutex_next_owner - return the next owner of the lock
1726 * @lock: the rt lock query
1728 * Returns the next owner of the lock or NULL
1730 * Caller has to serialize against other accessors to the lock
1733 * Special API call for PI-futex support
1735 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1737 if (!rt_mutex_has_waiters(lock))
1740 return rt_mutex_top_waiter(lock)->task;
1744 * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
1745 * @lock: the rt_mutex we were woken on
1746 * @to: the timeout, null if none. hrtimer should already have
1748 * @waiter: the pre-initialized rt_mutex_waiter
1750 * Wait for the the lock acquisition started on our behalf by
1751 * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
1752 * rt_mutex_cleanup_proxy_lock().
1756 * <0 - error, one of -EINTR, -ETIMEDOUT
1758 * Special API call for PI-futex support
1760 int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
1761 struct hrtimer_sleeper *to,
1762 struct rt_mutex_waiter *waiter)
1766 raw_spin_lock_irq(&lock->wait_lock);
1767 /* sleep on the mutex */
1768 set_current_state(TASK_INTERRUPTIBLE);
1769 ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1771 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1772 * have to fix that up.
1774 fixup_rt_mutex_waiters(lock);
1775 raw_spin_unlock_irq(&lock->wait_lock);
1781 * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
1782 * @lock: the rt_mutex we were woken on
1783 * @waiter: the pre-initialized rt_mutex_waiter
1785 * Attempt to clean up after a failed rt_mutex_wait_proxy_lock().
1787 * Unless we acquired the lock; we're still enqueued on the wait-list and can
1788 * in fact still be granted ownership until we're removed. Therefore we can
1789 * find we are in fact the owner and must disregard the
1790 * rt_mutex_wait_proxy_lock() failure.
1793 * true - did the cleanup, we done.
1794 * false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
1795 * caller should disregards its return value.
1797 * Special API call for PI-futex support
1799 bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
1800 struct rt_mutex_waiter *waiter)
1802 bool cleanup = false;
1804 raw_spin_lock_irq(&lock->wait_lock);
1806 * Do an unconditional try-lock, this deals with the lock stealing
1807 * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
1808 * sets a NULL owner.
1810 * We're not interested in the return value, because the subsequent
1811 * test on rt_mutex_owner() will infer that. If the trylock succeeded,
1812 * we will own the lock and it will have removed the waiter. If we
1813 * failed the trylock, we're still not owner and we need to remove
1816 try_to_take_rt_mutex(lock, current, waiter);
1818 * Unless we're the owner; we're still enqueued on the wait_list.
1819 * So check if we became owner, if not, take us off the wait_list.
1821 if (rt_mutex_owner(lock) != current) {
1822 remove_waiter(lock, waiter);
1826 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1827 * have to fix that up.
1829 fixup_rt_mutex_waiters(lock);
1831 raw_spin_unlock_irq(&lock->wait_lock);