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1/*
2 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
3 *
4 * started by Ingo Molnar and Thomas Gleixner.
5 *
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
10 *
11 * See Documentation/rt-mutex-design.txt for details.
12 */
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>
19
20#include "rtmutex_common.h"
21
22/*
23 * lock->owner state tracking:
24 *
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.
27 *
28 * owner bit0
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**
34 *
35 * The fast atomic compare exchange based acquire and release is only
36 * possible when bit 0 of lock->owner is 0.
37 *
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.
42 *
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.
47 */
48
49static void
50rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
51{
52 unsigned long val = (unsigned long)owner;
53
54 if (rt_mutex_has_waiters(lock))
55 val |= RT_MUTEX_HAS_WAITERS;
56
57 lock->owner = (struct task_struct *)val;
58}
59
60static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
61{
62 lock->owner = (struct task_struct *)
63 ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
64}
65
66static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
67{
68 if (!rt_mutex_has_waiters(lock))
69 clear_rt_mutex_waiters(lock);
70}
71
72/*
73 * We can speed up the acquire/release, if the architecture
74 * supports cmpxchg and if there's no debugging state to be set up
75 */
76#if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
77# define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c)
78static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
79{
80 unsigned long owner, *p = (unsigned long *) &lock->owner;
81
82 do {
83 owner = *p;
84 } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
85}
86#else
87# define rt_mutex_cmpxchg(l,c,n) (0)
88static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
89{
90 lock->owner = (struct task_struct *)
91 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
92}
93#endif
94
95static inline int
96rt_mutex_waiter_less(struct rt_mutex_waiter *left,
97 struct rt_mutex_waiter *right)
98{
99 if (left->prio < right->prio)
100 return 1;
101
102 /*
103 * If both waiters have dl_prio(), we check the deadlines of the
104 * associated tasks.
105 * If left waiter has a dl_prio(), and we didn't return 1 above,
106 * then right waiter has a dl_prio() too.
107 */
108 if (dl_prio(left->prio))
109 return (left->task->dl.deadline < right->task->dl.deadline);
110
111 return 0;
112}
113
114static void
115rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
116{
117 struct rb_node **link = &lock->waiters.rb_node;
118 struct rb_node *parent = NULL;
119 struct rt_mutex_waiter *entry;
120 int leftmost = 1;
121
122 while (*link) {
123 parent = *link;
124 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
125 if (rt_mutex_waiter_less(waiter, entry)) {
126 link = &parent->rb_left;
127 } else {
128 link = &parent->rb_right;
129 leftmost = 0;
130 }
131 }
132
133 if (leftmost)
134 lock->waiters_leftmost = &waiter->tree_entry;
135
136 rb_link_node(&waiter->tree_entry, parent, link);
137 rb_insert_color(&waiter->tree_entry, &lock->waiters);
138}
139
140static void
141rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
142{
143 if (RB_EMPTY_NODE(&waiter->tree_entry))
144 return;
145
146 if (lock->waiters_leftmost == &waiter->tree_entry)
147 lock->waiters_leftmost = rb_next(&waiter->tree_entry);
148
149 rb_erase(&waiter->tree_entry, &lock->waiters);
150 RB_CLEAR_NODE(&waiter->tree_entry);
151}
152
153static void
154rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
155{
156 struct rb_node **link = &task->pi_waiters.rb_node;
157 struct rb_node *parent = NULL;
158 struct rt_mutex_waiter *entry;
159 int leftmost = 1;
160
161 while (*link) {
162 parent = *link;
163 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
164 if (rt_mutex_waiter_less(waiter, entry)) {
165 link = &parent->rb_left;
166 } else {
167 link = &parent->rb_right;
168 leftmost = 0;
169 }
170 }
171
172 if (leftmost)
173 task->pi_waiters_leftmost = &waiter->pi_tree_entry;
174
175 rb_link_node(&waiter->pi_tree_entry, parent, link);
176 rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
177}
178
179static void
180rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
181{
182 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
183 return;
184
185 if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
186 task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
187
188 rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
189 RB_CLEAR_NODE(&waiter->pi_tree_entry);
190}
191
192/*
193 * Calculate task priority from the waiter tree priority
194 *
195 * Return task->normal_prio when the waiter tree is empty or when
196 * the waiter is not allowed to do priority boosting
197 */
198int rt_mutex_getprio(struct task_struct *task)
199{
200 if (likely(!task_has_pi_waiters(task)))
201 return task->normal_prio;
202
203 return min(task_top_pi_waiter(task)->prio,
204 task->normal_prio);
205}
206
207struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
208{
209 if (likely(!task_has_pi_waiters(task)))
210 return NULL;
211
212 return task_top_pi_waiter(task)->task;
213}
214
215/*
216 * Called by sched_setscheduler() to check whether the priority change
217 * is overruled by a possible priority boosting.
218 */
219int rt_mutex_check_prio(struct task_struct *task, int newprio)
220{
221 if (!task_has_pi_waiters(task))
222 return 0;
223
224 return task_top_pi_waiter(task)->task->prio <= newprio;
225}
226
227/*
228 * Adjust the priority of a task, after its pi_waiters got modified.
229 *
230 * This can be both boosting and unboosting. task->pi_lock must be held.
231 */
232static void __rt_mutex_adjust_prio(struct task_struct *task)
233{
234 int prio = rt_mutex_getprio(task);
235
236 if (task->prio != prio || dl_prio(prio))
237 rt_mutex_setprio(task, prio);
238}
239
240/*
241 * Adjust task priority (undo boosting). Called from the exit path of
242 * rt_mutex_slowunlock() and rt_mutex_slowlock().
243 *
244 * (Note: We do this outside of the protection of lock->wait_lock to
245 * allow the lock to be taken while or before we readjust the priority
246 * of task. We do not use the spin_xx_mutex() variants here as we are
247 * outside of the debug path.)
248 */
249static void rt_mutex_adjust_prio(struct task_struct *task)
250{
251 unsigned long flags;
252
253 raw_spin_lock_irqsave(&task->pi_lock, flags);
254 __rt_mutex_adjust_prio(task);
255 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
256}
257
258/*
259 * Max number of times we'll walk the boosting chain:
260 */
261int max_lock_depth = 1024;
262
263/*
264 * Adjust the priority chain. Also used for deadlock detection.
265 * Decreases task's usage by one - may thus free the task.
266 *
267 * @task: the task owning the mutex (owner) for which a chain walk is probably
268 * needed
269 * @deadlock_detect: do we have to carry out deadlock detection?
270 * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
271 * things for a task that has just got its priority adjusted, and
272 * is waiting on a mutex)
273 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
274 * its priority to the mutex owner (can be NULL in the case
275 * depicted above or if the top waiter is gone away and we are
276 * actually deboosting the owner)
277 * @top_task: the current top waiter
278 *
279 * Returns 0 or -EDEADLK.
280 */
281static int rt_mutex_adjust_prio_chain(struct task_struct *task,
282 int deadlock_detect,
283 struct rt_mutex *orig_lock,
284 struct rt_mutex_waiter *orig_waiter,
285 struct task_struct *top_task)
286{
287 struct rt_mutex *lock;
288 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
289 int detect_deadlock, ret = 0, depth = 0;
290 unsigned long flags;
291
292 detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
293 deadlock_detect);
294
295 /*
296 * The (de)boosting is a step by step approach with a lot of
297 * pitfalls. We want this to be preemptible and we want hold a
298 * maximum of two locks per step. So we have to check
299 * carefully whether things change under us.
300 */
301 again:
302 if (++depth > max_lock_depth) {
303 static int prev_max;
304
305 /*
306 * Print this only once. If the admin changes the limit,
307 * print a new message when reaching the limit again.
308 */
309 if (prev_max != max_lock_depth) {
310 prev_max = max_lock_depth;
311 printk(KERN_WARNING "Maximum lock depth %d reached "
312 "task: %s (%d)\n", max_lock_depth,
313 top_task->comm, task_pid_nr(top_task));
314 }
315 put_task_struct(task);
316
317 return deadlock_detect ? -EDEADLK : 0;
318 }
319 retry:
320 /*
321 * Task can not go away as we did a get_task() before !
322 */
323 raw_spin_lock_irqsave(&task->pi_lock, flags);
324
325 waiter = task->pi_blocked_on;
326 /*
327 * Check whether the end of the boosting chain has been
328 * reached or the state of the chain has changed while we
329 * dropped the locks.
330 */
331 if (!waiter)
332 goto out_unlock_pi;
333
334 /*
335 * Check the orig_waiter state. After we dropped the locks,
336 * the previous owner of the lock might have released the lock.
337 */
338 if (orig_waiter && !rt_mutex_owner(orig_lock))
339 goto out_unlock_pi;
340
341 /*
342 * Drop out, when the task has no waiters. Note,
343 * top_waiter can be NULL, when we are in the deboosting
344 * mode!
345 */
346 if (top_waiter) {
347 if (!task_has_pi_waiters(task))
348 goto out_unlock_pi;
349 /*
350 * If deadlock detection is off, we stop here if we
351 * are not the top pi waiter of the task.
352 */
353 if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
354 goto out_unlock_pi;
355 }
356
357 /*
358 * When deadlock detection is off then we check, if further
359 * priority adjustment is necessary.
360 */
361 if (!detect_deadlock && waiter->prio == task->prio)
362 goto out_unlock_pi;
363
364 lock = waiter->lock;
365 if (!raw_spin_trylock(&lock->wait_lock)) {
366 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
367 cpu_relax();
368 goto retry;
369 }
370
371 /*
372 * Deadlock detection. If the lock is the same as the original
373 * lock which caused us to walk the lock chain or if the
374 * current lock is owned by the task which initiated the chain
375 * walk, we detected a deadlock.
376 */
377 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
378 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
379 raw_spin_unlock(&lock->wait_lock);
380 ret = deadlock_detect ? -EDEADLK : 0;
381 goto out_unlock_pi;
382 }
383
384 top_waiter = rt_mutex_top_waiter(lock);
385
386 /* Requeue the waiter */
387 rt_mutex_dequeue(lock, waiter);
388 waiter->prio = task->prio;
389 rt_mutex_enqueue(lock, waiter);
390
391 /* Release the task */
392 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
393 if (!rt_mutex_owner(lock)) {
394 /*
395 * If the requeue above changed the top waiter, then we need
396 * to wake the new top waiter up to try to get the lock.
397 */
398
399 if (top_waiter != rt_mutex_top_waiter(lock))
400 wake_up_process(rt_mutex_top_waiter(lock)->task);
401 raw_spin_unlock(&lock->wait_lock);
402 goto out_put_task;
403 }
404 put_task_struct(task);
405
406 /* Grab the next task */
407 task = rt_mutex_owner(lock);
408 get_task_struct(task);
409 raw_spin_lock_irqsave(&task->pi_lock, flags);
410
411 if (waiter == rt_mutex_top_waiter(lock)) {
412 /* Boost the owner */
413 rt_mutex_dequeue_pi(task, top_waiter);
414 rt_mutex_enqueue_pi(task, waiter);
415 __rt_mutex_adjust_prio(task);
416
417 } else if (top_waiter == waiter) {
418 /* Deboost the owner */
419 rt_mutex_dequeue_pi(task, waiter);
420 waiter = rt_mutex_top_waiter(lock);
421 rt_mutex_enqueue_pi(task, waiter);
422 __rt_mutex_adjust_prio(task);
423 }
424
425 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
426
427 top_waiter = rt_mutex_top_waiter(lock);
428 raw_spin_unlock(&lock->wait_lock);
429
430 if (!detect_deadlock && waiter != top_waiter)
431 goto out_put_task;
432
433 goto again;
434
435 out_unlock_pi:
436 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
437 out_put_task:
438 put_task_struct(task);
439
440 return ret;
441}
442
443/*
444 * Try to take an rt-mutex
445 *
446 * Must be called with lock->wait_lock held.
447 *
448 * @lock: the lock to be acquired.
449 * @task: the task which wants to acquire the lock
450 * @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
451 */
452static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
453 struct rt_mutex_waiter *waiter)
454{
455 /*
456 * We have to be careful here if the atomic speedups are
457 * enabled, such that, when
458 * - no other waiter is on the lock
459 * - the lock has been released since we did the cmpxchg
460 * the lock can be released or taken while we are doing the
461 * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
462 *
463 * The atomic acquire/release aware variant of
464 * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
465 * the WAITERS bit, the atomic release / acquire can not
466 * happen anymore and lock->wait_lock protects us from the
467 * non-atomic case.
468 *
469 * Note, that this might set lock->owner =
470 * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
471 * any more. This is fixed up when we take the ownership.
472 * This is the transitional state explained at the top of this file.
473 */
474 mark_rt_mutex_waiters(lock);
475
476 if (rt_mutex_owner(lock))
477 return 0;
478
479 /*
480 * It will get the lock because of one of these conditions:
481 * 1) there is no waiter
482 * 2) higher priority than waiters
483 * 3) it is top waiter
484 */
485 if (rt_mutex_has_waiters(lock)) {
486 if (task->prio >= rt_mutex_top_waiter(lock)->prio) {
487 if (!waiter || waiter != rt_mutex_top_waiter(lock))
488 return 0;
489 }
490 }
491
492 if (waiter || rt_mutex_has_waiters(lock)) {
493 unsigned long flags;
494 struct rt_mutex_waiter *top;
495
496 raw_spin_lock_irqsave(&task->pi_lock, flags);
497
498 /* remove the queued waiter. */
499 if (waiter) {
500 rt_mutex_dequeue(lock, waiter);
501 task->pi_blocked_on = NULL;
502 }
503
504 /*
505 * We have to enqueue the top waiter(if it exists) into
506 * task->pi_waiters list.
507 */
508 if (rt_mutex_has_waiters(lock)) {
509 top = rt_mutex_top_waiter(lock);
510 rt_mutex_enqueue_pi(task, top);
511 }
512 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
513 }
514
515 /* We got the lock. */
516 debug_rt_mutex_lock(lock);
517
518 rt_mutex_set_owner(lock, task);
519
520 rt_mutex_deadlock_account_lock(lock, task);
521
522 return 1;
523}
524
525/*
526 * Task blocks on lock.
527 *
528 * Prepare waiter and propagate pi chain
529 *
530 * This must be called with lock->wait_lock held.
531 */
532static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
533 struct rt_mutex_waiter *waiter,
534 struct task_struct *task,
535 int detect_deadlock)
536{
537 struct task_struct *owner = rt_mutex_owner(lock);
538 struct rt_mutex_waiter *top_waiter = waiter;
539 unsigned long flags;
540 int chain_walk = 0, res;
541
542 /*
543 * Early deadlock detection. We really don't want the task to
544 * enqueue on itself just to untangle the mess later. It's not
545 * only an optimization. We drop the locks, so another waiter
546 * can come in before the chain walk detects the deadlock. So
547 * the other will detect the deadlock and return -EDEADLOCK,
548 * which is wrong, as the other waiter is not in a deadlock
549 * situation.
550 */
551 if (detect_deadlock && owner == task)
552 return -EDEADLK;
553
554 raw_spin_lock_irqsave(&task->pi_lock, flags);
555 __rt_mutex_adjust_prio(task);
556 waiter->task = task;
557 waiter->lock = lock;
558 waiter->prio = task->prio;
559
560 /* Get the top priority waiter on the lock */
561 if (rt_mutex_has_waiters(lock))
562 top_waiter = rt_mutex_top_waiter(lock);
563 rt_mutex_enqueue(lock, waiter);
564
565 task->pi_blocked_on = waiter;
566
567 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
568
569 if (!owner)
570 return 0;
571
572 if (waiter == rt_mutex_top_waiter(lock)) {
573 raw_spin_lock_irqsave(&owner->pi_lock, flags);
574 rt_mutex_dequeue_pi(owner, top_waiter);
575 rt_mutex_enqueue_pi(owner, waiter);
576
577 __rt_mutex_adjust_prio(owner);
578 if (owner->pi_blocked_on)
579 chain_walk = 1;
580 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
581 }
582 else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
583 chain_walk = 1;
584
585 if (!chain_walk)
586 return 0;
587
588 /*
589 * The owner can't disappear while holding a lock,
590 * so the owner struct is protected by wait_lock.
591 * Gets dropped in rt_mutex_adjust_prio_chain()!
592 */
593 get_task_struct(owner);
594
595 raw_spin_unlock(&lock->wait_lock);
596
597 res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
598 task);
599
600 raw_spin_lock(&lock->wait_lock);
601
602 return res;
603}
604
605/*
606 * Wake up the next waiter on the lock.
607 *
608 * Remove the top waiter from the current tasks waiter list and wake it up.
609 *
610 * Called with lock->wait_lock held.
611 */
612static void wakeup_next_waiter(struct rt_mutex *lock)
613{
614 struct rt_mutex_waiter *waiter;
615 unsigned long flags;
616
617 raw_spin_lock_irqsave(¤t->pi_lock, flags);
618
619 waiter = rt_mutex_top_waiter(lock);
620
621 /*
622 * Remove it from current->pi_waiters. We do not adjust a
623 * possible priority boost right now. We execute wakeup in the
624 * boosted mode and go back to normal after releasing
625 * lock->wait_lock.
626 */
627 rt_mutex_dequeue_pi(current, waiter);
628
629 rt_mutex_set_owner(lock, NULL);
630
631 raw_spin_unlock_irqrestore(¤t->pi_lock, flags);
632
633 wake_up_process(waiter->task);
634}
635
636/*
637 * Remove a waiter from a lock and give up
638 *
639 * Must be called with lock->wait_lock held and
640 * have just failed to try_to_take_rt_mutex().
641 */
642static void remove_waiter(struct rt_mutex *lock,
643 struct rt_mutex_waiter *waiter)
644{
645 int first = (waiter == rt_mutex_top_waiter(lock));
646 struct task_struct *owner = rt_mutex_owner(lock);
647 unsigned long flags;
648 int chain_walk = 0;
649
650 raw_spin_lock_irqsave(¤t->pi_lock, flags);
651 rt_mutex_dequeue(lock, waiter);
652 current->pi_blocked_on = NULL;
653 raw_spin_unlock_irqrestore(¤t->pi_lock, flags);
654
655 if (!owner)
656 return;
657
658 if (first) {
659
660 raw_spin_lock_irqsave(&owner->pi_lock, flags);
661
662 rt_mutex_dequeue_pi(owner, waiter);
663
664 if (rt_mutex_has_waiters(lock)) {
665 struct rt_mutex_waiter *next;
666
667 next = rt_mutex_top_waiter(lock);
668 rt_mutex_enqueue_pi(owner, next);
669 }
670 __rt_mutex_adjust_prio(owner);
671
672 if (owner->pi_blocked_on)
673 chain_walk = 1;
674
675 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
676 }
677
678 if (!chain_walk)
679 return;
680
681 /* gets dropped in rt_mutex_adjust_prio_chain()! */
682 get_task_struct(owner);
683
684 raw_spin_unlock(&lock->wait_lock);
685
686 rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
687
688 raw_spin_lock(&lock->wait_lock);
689}
690
691/*
692 * Recheck the pi chain, in case we got a priority setting
693 *
694 * Called from sched_setscheduler
695 */
696void rt_mutex_adjust_pi(struct task_struct *task)
697{
698 struct rt_mutex_waiter *waiter;
699 unsigned long flags;
700
701 raw_spin_lock_irqsave(&task->pi_lock, flags);
702
703 waiter = task->pi_blocked_on;
704 if (!waiter || (waiter->prio == task->prio &&
705 !dl_prio(task->prio))) {
706 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
707 return;
708 }
709
710 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
711
712 /* gets dropped in rt_mutex_adjust_prio_chain()! */
713 get_task_struct(task);
714 rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
715}
716
717/**
718 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
719 * @lock: the rt_mutex to take
720 * @state: the state the task should block in (TASK_INTERRUPTIBLE
721 * or TASK_UNINTERRUPTIBLE)
722 * @timeout: the pre-initialized and started timer, or NULL for none
723 * @waiter: the pre-initialized rt_mutex_waiter
724 *
725 * lock->wait_lock must be held by the caller.
726 */
727static int __sched
728__rt_mutex_slowlock(struct rt_mutex *lock, int state,
729 struct hrtimer_sleeper *timeout,
730 struct rt_mutex_waiter *waiter)
731{
732 int ret = 0;
733
734 for (;;) {
735 /* Try to acquire the lock: */
736 if (try_to_take_rt_mutex(lock, current, waiter))
737 break;
738
739 /*
740 * TASK_INTERRUPTIBLE checks for signals and
741 * timeout. Ignored otherwise.
742 */
743 if (unlikely(state == TASK_INTERRUPTIBLE)) {
744 /* Signal pending? */
745 if (signal_pending(current))
746 ret = -EINTR;
747 if (timeout && !timeout->task)
748 ret = -ETIMEDOUT;
749 if (ret)
750 break;
751 }
752
753 raw_spin_unlock(&lock->wait_lock);
754
755 debug_rt_mutex_print_deadlock(waiter);
756
757 schedule_rt_mutex(lock);
758
759 raw_spin_lock(&lock->wait_lock);
760 set_current_state(state);
761 }
762
763 return ret;
764}
765
766/*
767 * Slow path lock function:
768 */
769static int __sched
770rt_mutex_slowlock(struct rt_mutex *lock, int state,
771 struct hrtimer_sleeper *timeout,
772 int detect_deadlock)
773{
774 struct rt_mutex_waiter waiter;
775 int ret = 0;
776
777 debug_rt_mutex_init_waiter(&waiter);
778 RB_CLEAR_NODE(&waiter.pi_tree_entry);
779 RB_CLEAR_NODE(&waiter.tree_entry);
780
781 raw_spin_lock(&lock->wait_lock);
782
783 /* Try to acquire the lock again: */
784 if (try_to_take_rt_mutex(lock, current, NULL)) {
785 raw_spin_unlock(&lock->wait_lock);
786 return 0;
787 }
788
789 set_current_state(state);
790
791 /* Setup the timer, when timeout != NULL */
792 if (unlikely(timeout)) {
793 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
794 if (!hrtimer_active(&timeout->timer))
795 timeout->task = NULL;
796 }
797
798 ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
799
800 if (likely(!ret))
801 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
802
803 set_current_state(TASK_RUNNING);
804
805 if (unlikely(ret))
806 remove_waiter(lock, &waiter);
807
808 /*
809 * try_to_take_rt_mutex() sets the waiter bit
810 * unconditionally. We might have to fix that up.
811 */
812 fixup_rt_mutex_waiters(lock);
813
814 raw_spin_unlock(&lock->wait_lock);
815
816 /* Remove pending timer: */
817 if (unlikely(timeout))
818 hrtimer_cancel(&timeout->timer);
819
820 debug_rt_mutex_free_waiter(&waiter);
821
822 return ret;
823}
824
825/*
826 * Slow path try-lock function:
827 */
828static inline int
829rt_mutex_slowtrylock(struct rt_mutex *lock)
830{
831 int ret = 0;
832
833 raw_spin_lock(&lock->wait_lock);
834
835 if (likely(rt_mutex_owner(lock) != current)) {
836
837 ret = try_to_take_rt_mutex(lock, current, NULL);
838 /*
839 * try_to_take_rt_mutex() sets the lock waiters
840 * bit unconditionally. Clean this up.
841 */
842 fixup_rt_mutex_waiters(lock);
843 }
844
845 raw_spin_unlock(&lock->wait_lock);
846
847 return ret;
848}
849
850/*
851 * Slow path to release a rt-mutex:
852 */
853static void __sched
854rt_mutex_slowunlock(struct rt_mutex *lock)
855{
856 raw_spin_lock(&lock->wait_lock);
857
858 debug_rt_mutex_unlock(lock);
859
860 rt_mutex_deadlock_account_unlock(current);
861
862 if (!rt_mutex_has_waiters(lock)) {
863 lock->owner = NULL;
864 raw_spin_unlock(&lock->wait_lock);
865 return;
866 }
867
868 wakeup_next_waiter(lock);
869
870 raw_spin_unlock(&lock->wait_lock);
871
872 /* Undo pi boosting if necessary: */
873 rt_mutex_adjust_prio(current);
874}
875
876/*
877 * debug aware fast / slowpath lock,trylock,unlock
878 *
879 * The atomic acquire/release ops are compiled away, when either the
880 * architecture does not support cmpxchg or when debugging is enabled.
881 */
882static inline int
883rt_mutex_fastlock(struct rt_mutex *lock, int state,
884 int detect_deadlock,
885 int (*slowfn)(struct rt_mutex *lock, int state,
886 struct hrtimer_sleeper *timeout,
887 int detect_deadlock))
888{
889 if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
890 rt_mutex_deadlock_account_lock(lock, current);
891 return 0;
892 } else
893 return slowfn(lock, state, NULL, detect_deadlock);
894}
895
896static inline int
897rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
898 struct hrtimer_sleeper *timeout, int detect_deadlock,
899 int (*slowfn)(struct rt_mutex *lock, int state,
900 struct hrtimer_sleeper *timeout,
901 int detect_deadlock))
902{
903 if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
904 rt_mutex_deadlock_account_lock(lock, current);
905 return 0;
906 } else
907 return slowfn(lock, state, timeout, detect_deadlock);
908}
909
910static inline int
911rt_mutex_fasttrylock(struct rt_mutex *lock,
912 int (*slowfn)(struct rt_mutex *lock))
913{
914 if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
915 rt_mutex_deadlock_account_lock(lock, current);
916 return 1;
917 }
918 return slowfn(lock);
919}
920
921static inline void
922rt_mutex_fastunlock(struct rt_mutex *lock,
923 void (*slowfn)(struct rt_mutex *lock))
924{
925 if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
926 rt_mutex_deadlock_account_unlock(current);
927 else
928 slowfn(lock);
929}
930
931/**
932 * rt_mutex_lock - lock a rt_mutex
933 *
934 * @lock: the rt_mutex to be locked
935 */
936void __sched rt_mutex_lock(struct rt_mutex *lock)
937{
938 might_sleep();
939
940 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
941}
942EXPORT_SYMBOL_GPL(rt_mutex_lock);
943
944/**
945 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
946 *
947 * @lock: the rt_mutex to be locked
948 * @detect_deadlock: deadlock detection on/off
949 *
950 * Returns:
951 * 0 on success
952 * -EINTR when interrupted by a signal
953 * -EDEADLK when the lock would deadlock (when deadlock detection is on)
954 */
955int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
956 int detect_deadlock)
957{
958 might_sleep();
959
960 return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
961 detect_deadlock, rt_mutex_slowlock);
962}
963EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
964
965/**
966 * rt_mutex_timed_lock - lock a rt_mutex interruptible
967 * the timeout structure is provided
968 * by the caller
969 *
970 * @lock: the rt_mutex to be locked
971 * @timeout: timeout structure or NULL (no timeout)
972 * @detect_deadlock: deadlock detection on/off
973 *
974 * Returns:
975 * 0 on success
976 * -EINTR when interrupted by a signal
977 * -ETIMEDOUT when the timeout expired
978 * -EDEADLK when the lock would deadlock (when deadlock detection is on)
979 */
980int
981rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
982 int detect_deadlock)
983{
984 might_sleep();
985
986 return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
987 detect_deadlock, rt_mutex_slowlock);
988}
989EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
990
991/**
992 * rt_mutex_trylock - try to lock a rt_mutex
993 *
994 * @lock: the rt_mutex to be locked
995 *
996 * Returns 1 on success and 0 on contention
997 */
998int __sched rt_mutex_trylock(struct rt_mutex *lock)
999{
1000 return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1001}
1002EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1003
1004/**
1005 * rt_mutex_unlock - unlock a rt_mutex
1006 *
1007 * @lock: the rt_mutex to be unlocked
1008 */
1009void __sched rt_mutex_unlock(struct rt_mutex *lock)
1010{
1011 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1012}
1013EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1014
1015/**
1016 * rt_mutex_destroy - mark a mutex unusable
1017 * @lock: the mutex to be destroyed
1018 *
1019 * This function marks the mutex uninitialized, and any subsequent
1020 * use of the mutex is forbidden. The mutex must not be locked when
1021 * this function is called.
1022 */
1023void rt_mutex_destroy(struct rt_mutex *lock)
1024{
1025 WARN_ON(rt_mutex_is_locked(lock));
1026#ifdef CONFIG_DEBUG_RT_MUTEXES
1027 lock->magic = NULL;
1028#endif
1029}
1030
1031EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1032
1033/**
1034 * __rt_mutex_init - initialize the rt lock
1035 *
1036 * @lock: the rt lock to be initialized
1037 *
1038 * Initialize the rt lock to unlocked state.
1039 *
1040 * Initializing of a locked rt lock is not allowed
1041 */
1042void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1043{
1044 lock->owner = NULL;
1045 raw_spin_lock_init(&lock->wait_lock);
1046 lock->waiters = RB_ROOT;
1047 lock->waiters_leftmost = NULL;
1048
1049 debug_rt_mutex_init(lock, name);
1050}
1051EXPORT_SYMBOL_GPL(__rt_mutex_init);
1052
1053/**
1054 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1055 * proxy owner
1056 *
1057 * @lock: the rt_mutex to be locked
1058 * @proxy_owner:the task to set as owner
1059 *
1060 * No locking. Caller has to do serializing itself
1061 * Special API call for PI-futex support
1062 */
1063void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1064 struct task_struct *proxy_owner)
1065{
1066 __rt_mutex_init(lock, NULL);
1067 debug_rt_mutex_proxy_lock(lock, proxy_owner);
1068 rt_mutex_set_owner(lock, proxy_owner);
1069 rt_mutex_deadlock_account_lock(lock, proxy_owner);
1070}
1071
1072/**
1073 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1074 *
1075 * @lock: the rt_mutex to be locked
1076 *
1077 * No locking. Caller has to do serializing itself
1078 * Special API call for PI-futex support
1079 */
1080void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1081 struct task_struct *proxy_owner)
1082{
1083 debug_rt_mutex_proxy_unlock(lock);
1084 rt_mutex_set_owner(lock, NULL);
1085 rt_mutex_deadlock_account_unlock(proxy_owner);
1086}
1087
1088/**
1089 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1090 * @lock: the rt_mutex to take
1091 * @waiter: the pre-initialized rt_mutex_waiter
1092 * @task: the task to prepare
1093 * @detect_deadlock: perform deadlock detection (1) or not (0)
1094 *
1095 * Returns:
1096 * 0 - task blocked on lock
1097 * 1 - acquired the lock for task, caller should wake it up
1098 * <0 - error
1099 *
1100 * Special API call for FUTEX_REQUEUE_PI support.
1101 */
1102int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1103 struct rt_mutex_waiter *waiter,
1104 struct task_struct *task, int detect_deadlock)
1105{
1106 int ret;
1107
1108 raw_spin_lock(&lock->wait_lock);
1109
1110 if (try_to_take_rt_mutex(lock, task, NULL)) {
1111 raw_spin_unlock(&lock->wait_lock);
1112 return 1;
1113 }
1114
1115 ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
1116
1117 if (ret && !rt_mutex_owner(lock)) {
1118 /*
1119 * Reset the return value. We might have
1120 * returned with -EDEADLK and the owner
1121 * released the lock while we were walking the
1122 * pi chain. Let the waiter sort it out.
1123 */
1124 ret = 0;
1125 }
1126
1127 if (unlikely(ret))
1128 remove_waiter(lock, waiter);
1129
1130 raw_spin_unlock(&lock->wait_lock);
1131
1132 debug_rt_mutex_print_deadlock(waiter);
1133
1134 return ret;
1135}
1136
1137/**
1138 * rt_mutex_next_owner - return the next owner of the lock
1139 *
1140 * @lock: the rt lock query
1141 *
1142 * Returns the next owner of the lock or NULL
1143 *
1144 * Caller has to serialize against other accessors to the lock
1145 * itself.
1146 *
1147 * Special API call for PI-futex support
1148 */
1149struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1150{
1151 if (!rt_mutex_has_waiters(lock))
1152 return NULL;
1153
1154 return rt_mutex_top_waiter(lock)->task;
1155}
1156
1157/**
1158 * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1159 * @lock: the rt_mutex we were woken on
1160 * @to: the timeout, null if none. hrtimer should already have
1161 * been started.
1162 * @waiter: the pre-initialized rt_mutex_waiter
1163 * @detect_deadlock: perform deadlock detection (1) or not (0)
1164 *
1165 * Complete the lock acquisition started our behalf by another thread.
1166 *
1167 * Returns:
1168 * 0 - success
1169 * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1170 *
1171 * Special API call for PI-futex requeue support
1172 */
1173int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1174 struct hrtimer_sleeper *to,
1175 struct rt_mutex_waiter *waiter,
1176 int detect_deadlock)
1177{
1178 int ret;
1179
1180 raw_spin_lock(&lock->wait_lock);
1181
1182 set_current_state(TASK_INTERRUPTIBLE);
1183
1184 ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1185
1186 set_current_state(TASK_RUNNING);
1187
1188 if (unlikely(ret))
1189 remove_waiter(lock, waiter);
1190
1191 /*
1192 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1193 * have to fix that up.
1194 */
1195 fixup_rt_mutex_waiters(lock);
1196
1197 raw_spin_unlock(&lock->wait_lock);
1198
1199 return ret;
1200}
1/*
2 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
3 *
4 * started by Ingo Molnar and Thomas Gleixner.
5 *
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
10 *
11 * See Documentation/locking/rt-mutex-design.txt for details.
12 */
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>
19
20#include "rtmutex_common.h"
21
22/*
23 * lock->owner state tracking:
24 *
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.
27 *
28 * owner bit0
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**
34 *
35 * The fast atomic compare exchange based acquire and release is only
36 * possible when bit 0 of lock->owner is 0.
37 *
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.
42 *
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.
47 */
48
49static void
50rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
51{
52 unsigned long val = (unsigned long)owner;
53
54 if (rt_mutex_has_waiters(lock))
55 val |= RT_MUTEX_HAS_WAITERS;
56
57 lock->owner = (struct task_struct *)val;
58}
59
60static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
61{
62 lock->owner = (struct task_struct *)
63 ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
64}
65
66static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
67{
68 if (!rt_mutex_has_waiters(lock))
69 clear_rt_mutex_waiters(lock);
70}
71
72/*
73 * We can speed up the acquire/release, if there's no debugging state to be
74 * set up.
75 */
76#ifndef CONFIG_DEBUG_RT_MUTEXES
77# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
78# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
79# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
80
81/*
82 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
83 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
84 * relaxed semantics suffice.
85 */
86static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
87{
88 unsigned long owner, *p = (unsigned long *) &lock->owner;
89
90 do {
91 owner = *p;
92 } while (cmpxchg_relaxed(p, owner,
93 owner | RT_MUTEX_HAS_WAITERS) != owner);
94}
95
96/*
97 * Safe fastpath aware unlock:
98 * 1) Clear the waiters bit
99 * 2) Drop lock->wait_lock
100 * 3) Try to unlock the lock with cmpxchg
101 */
102static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
103 unsigned long flags)
104 __releases(lock->wait_lock)
105{
106 struct task_struct *owner = rt_mutex_owner(lock);
107
108 clear_rt_mutex_waiters(lock);
109 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
110 /*
111 * If a new waiter comes in between the unlock and the cmpxchg
112 * we have two situations:
113 *
114 * unlock(wait_lock);
115 * lock(wait_lock);
116 * cmpxchg(p, owner, 0) == owner
117 * mark_rt_mutex_waiters(lock);
118 * acquire(lock);
119 * or:
120 *
121 * unlock(wait_lock);
122 * lock(wait_lock);
123 * mark_rt_mutex_waiters(lock);
124 *
125 * cmpxchg(p, owner, 0) != owner
126 * enqueue_waiter();
127 * unlock(wait_lock);
128 * lock(wait_lock);
129 * wake waiter();
130 * unlock(wait_lock);
131 * lock(wait_lock);
132 * acquire(lock);
133 */
134 return rt_mutex_cmpxchg_release(lock, owner, NULL);
135}
136
137#else
138# define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
139# define rt_mutex_cmpxchg_acquire(l,c,n) (0)
140# define rt_mutex_cmpxchg_release(l,c,n) (0)
141
142static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
143{
144 lock->owner = (struct task_struct *)
145 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
146}
147
148/*
149 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
150 */
151static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
152 unsigned long flags)
153 __releases(lock->wait_lock)
154{
155 lock->owner = NULL;
156 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
157 return true;
158}
159#endif
160
161static inline int
162rt_mutex_waiter_less(struct rt_mutex_waiter *left,
163 struct rt_mutex_waiter *right)
164{
165 if (left->prio < right->prio)
166 return 1;
167
168 /*
169 * If both waiters have dl_prio(), we check the deadlines of the
170 * associated tasks.
171 * If left waiter has a dl_prio(), and we didn't return 1 above,
172 * then right waiter has a dl_prio() too.
173 */
174 if (dl_prio(left->prio))
175 return dl_time_before(left->task->dl.deadline,
176 right->task->dl.deadline);
177
178 return 0;
179}
180
181static void
182rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
183{
184 struct rb_node **link = &lock->waiters.rb_node;
185 struct rb_node *parent = NULL;
186 struct rt_mutex_waiter *entry;
187 int leftmost = 1;
188
189 while (*link) {
190 parent = *link;
191 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
192 if (rt_mutex_waiter_less(waiter, entry)) {
193 link = &parent->rb_left;
194 } else {
195 link = &parent->rb_right;
196 leftmost = 0;
197 }
198 }
199
200 if (leftmost)
201 lock->waiters_leftmost = &waiter->tree_entry;
202
203 rb_link_node(&waiter->tree_entry, parent, link);
204 rb_insert_color(&waiter->tree_entry, &lock->waiters);
205}
206
207static void
208rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
209{
210 if (RB_EMPTY_NODE(&waiter->tree_entry))
211 return;
212
213 if (lock->waiters_leftmost == &waiter->tree_entry)
214 lock->waiters_leftmost = rb_next(&waiter->tree_entry);
215
216 rb_erase(&waiter->tree_entry, &lock->waiters);
217 RB_CLEAR_NODE(&waiter->tree_entry);
218}
219
220static void
221rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
222{
223 struct rb_node **link = &task->pi_waiters.rb_node;
224 struct rb_node *parent = NULL;
225 struct rt_mutex_waiter *entry;
226 int leftmost = 1;
227
228 while (*link) {
229 parent = *link;
230 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
231 if (rt_mutex_waiter_less(waiter, entry)) {
232 link = &parent->rb_left;
233 } else {
234 link = &parent->rb_right;
235 leftmost = 0;
236 }
237 }
238
239 if (leftmost)
240 task->pi_waiters_leftmost = &waiter->pi_tree_entry;
241
242 rb_link_node(&waiter->pi_tree_entry, parent, link);
243 rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
244}
245
246static void
247rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
248{
249 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
250 return;
251
252 if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
253 task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
254
255 rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
256 RB_CLEAR_NODE(&waiter->pi_tree_entry);
257}
258
259/*
260 * Calculate task priority from the waiter tree priority
261 *
262 * Return task->normal_prio when the waiter tree is empty or when
263 * the waiter is not allowed to do priority boosting
264 */
265int rt_mutex_getprio(struct task_struct *task)
266{
267 if (likely(!task_has_pi_waiters(task)))
268 return task->normal_prio;
269
270 return min(task_top_pi_waiter(task)->prio,
271 task->normal_prio);
272}
273
274struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
275{
276 if (likely(!task_has_pi_waiters(task)))
277 return NULL;
278
279 return task_top_pi_waiter(task)->task;
280}
281
282/*
283 * Called by sched_setscheduler() to get the priority which will be
284 * effective after the change.
285 */
286int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
287{
288 if (!task_has_pi_waiters(task))
289 return newprio;
290
291 if (task_top_pi_waiter(task)->task->prio <= newprio)
292 return task_top_pi_waiter(task)->task->prio;
293 return newprio;
294}
295
296/*
297 * Adjust the priority of a task, after its pi_waiters got modified.
298 *
299 * This can be both boosting and unboosting. task->pi_lock must be held.
300 */
301static void __rt_mutex_adjust_prio(struct task_struct *task)
302{
303 int prio = rt_mutex_getprio(task);
304
305 if (task->prio != prio || dl_prio(prio))
306 rt_mutex_setprio(task, prio);
307}
308
309/*
310 * Adjust task priority (undo boosting). Called from the exit path of
311 * rt_mutex_slowunlock() and rt_mutex_slowlock().
312 *
313 * (Note: We do this outside of the protection of lock->wait_lock to
314 * allow the lock to be taken while or before we readjust the priority
315 * of task. We do not use the spin_xx_mutex() variants here as we are
316 * outside of the debug path.)
317 */
318void rt_mutex_adjust_prio(struct task_struct *task)
319{
320 unsigned long flags;
321
322 raw_spin_lock_irqsave(&task->pi_lock, flags);
323 __rt_mutex_adjust_prio(task);
324 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
325}
326
327/*
328 * Deadlock detection is conditional:
329 *
330 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
331 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
332 *
333 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
334 * conducted independent of the detect argument.
335 *
336 * If the waiter argument is NULL this indicates the deboost path and
337 * deadlock detection is disabled independent of the detect argument
338 * and the config settings.
339 */
340static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
341 enum rtmutex_chainwalk chwalk)
342{
343 /*
344 * This is just a wrapper function for the following call,
345 * because debug_rt_mutex_detect_deadlock() smells like a magic
346 * debug feature and I wanted to keep the cond function in the
347 * main source file along with the comments instead of having
348 * two of the same in the headers.
349 */
350 return debug_rt_mutex_detect_deadlock(waiter, chwalk);
351}
352
353/*
354 * Max number of times we'll walk the boosting chain:
355 */
356int max_lock_depth = 1024;
357
358static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
359{
360 return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
361}
362
363/*
364 * Adjust the priority chain. Also used for deadlock detection.
365 * Decreases task's usage by one - may thus free the task.
366 *
367 * @task: the task owning the mutex (owner) for which a chain walk is
368 * probably needed
369 * @chwalk: do we have to carry out deadlock detection?
370 * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
371 * things for a task that has just got its priority adjusted, and
372 * is waiting on a mutex)
373 * @next_lock: the mutex on which the owner of @orig_lock was blocked before
374 * we dropped its pi_lock. Is never dereferenced, only used for
375 * comparison to detect lock chain changes.
376 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
377 * its priority to the mutex owner (can be NULL in the case
378 * depicted above or if the top waiter is gone away and we are
379 * actually deboosting the owner)
380 * @top_task: the current top waiter
381 *
382 * Returns 0 or -EDEADLK.
383 *
384 * Chain walk basics and protection scope
385 *
386 * [R] refcount on task
387 * [P] task->pi_lock held
388 * [L] rtmutex->wait_lock held
389 *
390 * Step Description Protected by
391 * function arguments:
392 * @task [R]
393 * @orig_lock if != NULL @top_task is blocked on it
394 * @next_lock Unprotected. Cannot be
395 * dereferenced. Only used for
396 * comparison.
397 * @orig_waiter if != NULL @top_task is blocked on it
398 * @top_task current, or in case of proxy
399 * locking protected by calling
400 * code
401 * again:
402 * loop_sanity_check();
403 * retry:
404 * [1] lock(task->pi_lock); [R] acquire [P]
405 * [2] waiter = task->pi_blocked_on; [P]
406 * [3] check_exit_conditions_1(); [P]
407 * [4] lock = waiter->lock; [P]
408 * [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
409 * unlock(task->pi_lock); release [P]
410 * goto retry;
411 * }
412 * [6] check_exit_conditions_2(); [P] + [L]
413 * [7] requeue_lock_waiter(lock, waiter); [P] + [L]
414 * [8] unlock(task->pi_lock); release [P]
415 * put_task_struct(task); release [R]
416 * [9] check_exit_conditions_3(); [L]
417 * [10] task = owner(lock); [L]
418 * get_task_struct(task); [L] acquire [R]
419 * lock(task->pi_lock); [L] acquire [P]
420 * [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
421 * [12] check_exit_conditions_4(); [P] + [L]
422 * [13] unlock(task->pi_lock); release [P]
423 * unlock(lock->wait_lock); release [L]
424 * goto again;
425 */
426static int rt_mutex_adjust_prio_chain(struct task_struct *task,
427 enum rtmutex_chainwalk chwalk,
428 struct rt_mutex *orig_lock,
429 struct rt_mutex *next_lock,
430 struct rt_mutex_waiter *orig_waiter,
431 struct task_struct *top_task)
432{
433 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
434 struct rt_mutex_waiter *prerequeue_top_waiter;
435 int ret = 0, depth = 0;
436 struct rt_mutex *lock;
437 bool detect_deadlock;
438 bool requeue = true;
439
440 detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
441
442 /*
443 * The (de)boosting is a step by step approach with a lot of
444 * pitfalls. We want this to be preemptible and we want hold a
445 * maximum of two locks per step. So we have to check
446 * carefully whether things change under us.
447 */
448 again:
449 /*
450 * We limit the lock chain length for each invocation.
451 */
452 if (++depth > max_lock_depth) {
453 static int prev_max;
454
455 /*
456 * Print this only once. If the admin changes the limit,
457 * print a new message when reaching the limit again.
458 */
459 if (prev_max != max_lock_depth) {
460 prev_max = max_lock_depth;
461 printk(KERN_WARNING "Maximum lock depth %d reached "
462 "task: %s (%d)\n", max_lock_depth,
463 top_task->comm, task_pid_nr(top_task));
464 }
465 put_task_struct(task);
466
467 return -EDEADLK;
468 }
469
470 /*
471 * We are fully preemptible here and only hold the refcount on
472 * @task. So everything can have changed under us since the
473 * caller or our own code below (goto retry/again) dropped all
474 * locks.
475 */
476 retry:
477 /*
478 * [1] Task cannot go away as we did a get_task() before !
479 */
480 raw_spin_lock_irq(&task->pi_lock);
481
482 /*
483 * [2] Get the waiter on which @task is blocked on.
484 */
485 waiter = task->pi_blocked_on;
486
487 /*
488 * [3] check_exit_conditions_1() protected by task->pi_lock.
489 */
490
491 /*
492 * Check whether the end of the boosting chain has been
493 * reached or the state of the chain has changed while we
494 * dropped the locks.
495 */
496 if (!waiter)
497 goto out_unlock_pi;
498
499 /*
500 * Check the orig_waiter state. After we dropped the locks,
501 * the previous owner of the lock might have released the lock.
502 */
503 if (orig_waiter && !rt_mutex_owner(orig_lock))
504 goto out_unlock_pi;
505
506 /*
507 * We dropped all locks after taking a refcount on @task, so
508 * the task might have moved on in the lock chain or even left
509 * the chain completely and blocks now on an unrelated lock or
510 * on @orig_lock.
511 *
512 * We stored the lock on which @task was blocked in @next_lock,
513 * so we can detect the chain change.
514 */
515 if (next_lock != waiter->lock)
516 goto out_unlock_pi;
517
518 /*
519 * Drop out, when the task has no waiters. Note,
520 * top_waiter can be NULL, when we are in the deboosting
521 * mode!
522 */
523 if (top_waiter) {
524 if (!task_has_pi_waiters(task))
525 goto out_unlock_pi;
526 /*
527 * If deadlock detection is off, we stop here if we
528 * are not the top pi waiter of the task. If deadlock
529 * detection is enabled we continue, but stop the
530 * requeueing in the chain walk.
531 */
532 if (top_waiter != task_top_pi_waiter(task)) {
533 if (!detect_deadlock)
534 goto out_unlock_pi;
535 else
536 requeue = false;
537 }
538 }
539
540 /*
541 * If the waiter priority is the same as the task priority
542 * then there is no further priority adjustment necessary. If
543 * deadlock detection is off, we stop the chain walk. If its
544 * enabled we continue, but stop the requeueing in the chain
545 * walk.
546 */
547 if (waiter->prio == task->prio) {
548 if (!detect_deadlock)
549 goto out_unlock_pi;
550 else
551 requeue = false;
552 }
553
554 /*
555 * [4] Get the next lock
556 */
557 lock = waiter->lock;
558 /*
559 * [5] We need to trylock here as we are holding task->pi_lock,
560 * which is the reverse lock order versus the other rtmutex
561 * operations.
562 */
563 if (!raw_spin_trylock(&lock->wait_lock)) {
564 raw_spin_unlock_irq(&task->pi_lock);
565 cpu_relax();
566 goto retry;
567 }
568
569 /*
570 * [6] check_exit_conditions_2() protected by task->pi_lock and
571 * lock->wait_lock.
572 *
573 * Deadlock detection. If the lock is the same as the original
574 * lock which caused us to walk the lock chain or if the
575 * current lock is owned by the task which initiated the chain
576 * walk, we detected a deadlock.
577 */
578 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
579 debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
580 raw_spin_unlock(&lock->wait_lock);
581 ret = -EDEADLK;
582 goto out_unlock_pi;
583 }
584
585 /*
586 * If we just follow the lock chain for deadlock detection, no
587 * need to do all the requeue operations. To avoid a truckload
588 * of conditionals around the various places below, just do the
589 * minimum chain walk checks.
590 */
591 if (!requeue) {
592 /*
593 * No requeue[7] here. Just release @task [8]
594 */
595 raw_spin_unlock(&task->pi_lock);
596 put_task_struct(task);
597
598 /*
599 * [9] check_exit_conditions_3 protected by lock->wait_lock.
600 * If there is no owner of the lock, end of chain.
601 */
602 if (!rt_mutex_owner(lock)) {
603 raw_spin_unlock_irq(&lock->wait_lock);
604 return 0;
605 }
606
607 /* [10] Grab the next task, i.e. owner of @lock */
608 task = rt_mutex_owner(lock);
609 get_task_struct(task);
610 raw_spin_lock(&task->pi_lock);
611
612 /*
613 * No requeue [11] here. We just do deadlock detection.
614 *
615 * [12] Store whether owner is blocked
616 * itself. Decision is made after dropping the locks
617 */
618 next_lock = task_blocked_on_lock(task);
619 /*
620 * Get the top waiter for the next iteration
621 */
622 top_waiter = rt_mutex_top_waiter(lock);
623
624 /* [13] Drop locks */
625 raw_spin_unlock(&task->pi_lock);
626 raw_spin_unlock_irq(&lock->wait_lock);
627
628 /* If owner is not blocked, end of chain. */
629 if (!next_lock)
630 goto out_put_task;
631 goto again;
632 }
633
634 /*
635 * Store the current top waiter before doing the requeue
636 * operation on @lock. We need it for the boost/deboost
637 * decision below.
638 */
639 prerequeue_top_waiter = rt_mutex_top_waiter(lock);
640
641 /* [7] Requeue the waiter in the lock waiter tree. */
642 rt_mutex_dequeue(lock, waiter);
643 waiter->prio = task->prio;
644 rt_mutex_enqueue(lock, waiter);
645
646 /* [8] Release the task */
647 raw_spin_unlock(&task->pi_lock);
648 put_task_struct(task);
649
650 /*
651 * [9] check_exit_conditions_3 protected by lock->wait_lock.
652 *
653 * We must abort the chain walk if there is no lock owner even
654 * in the dead lock detection case, as we have nothing to
655 * follow here. This is the end of the chain we are walking.
656 */
657 if (!rt_mutex_owner(lock)) {
658 /*
659 * If the requeue [7] above changed the top waiter,
660 * then we need to wake the new top waiter up to try
661 * to get the lock.
662 */
663 if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
664 wake_up_process(rt_mutex_top_waiter(lock)->task);
665 raw_spin_unlock_irq(&lock->wait_lock);
666 return 0;
667 }
668
669 /* [10] Grab the next task, i.e. the owner of @lock */
670 task = rt_mutex_owner(lock);
671 get_task_struct(task);
672 raw_spin_lock(&task->pi_lock);
673
674 /* [11] requeue the pi waiters if necessary */
675 if (waiter == rt_mutex_top_waiter(lock)) {
676 /*
677 * The waiter became the new top (highest priority)
678 * waiter on the lock. Replace the previous top waiter
679 * in the owner tasks pi waiters tree with this waiter
680 * and adjust the priority of the owner.
681 */
682 rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
683 rt_mutex_enqueue_pi(task, waiter);
684 __rt_mutex_adjust_prio(task);
685
686 } else if (prerequeue_top_waiter == waiter) {
687 /*
688 * The waiter was the top waiter on the lock, but is
689 * no longer the top prority waiter. Replace waiter in
690 * the owner tasks pi waiters tree with the new top
691 * (highest priority) waiter and adjust the priority
692 * of the owner.
693 * The new top waiter is stored in @waiter so that
694 * @waiter == @top_waiter evaluates to true below and
695 * we continue to deboost the rest of the chain.
696 */
697 rt_mutex_dequeue_pi(task, waiter);
698 waiter = rt_mutex_top_waiter(lock);
699 rt_mutex_enqueue_pi(task, waiter);
700 __rt_mutex_adjust_prio(task);
701 } else {
702 /*
703 * Nothing changed. No need to do any priority
704 * adjustment.
705 */
706 }
707
708 /*
709 * [12] check_exit_conditions_4() protected by task->pi_lock
710 * and lock->wait_lock. The actual decisions are made after we
711 * dropped the locks.
712 *
713 * Check whether the task which owns the current lock is pi
714 * blocked itself. If yes we store a pointer to the lock for
715 * the lock chain change detection above. After we dropped
716 * task->pi_lock next_lock cannot be dereferenced anymore.
717 */
718 next_lock = task_blocked_on_lock(task);
719 /*
720 * Store the top waiter of @lock for the end of chain walk
721 * decision below.
722 */
723 top_waiter = rt_mutex_top_waiter(lock);
724
725 /* [13] Drop the locks */
726 raw_spin_unlock(&task->pi_lock);
727 raw_spin_unlock_irq(&lock->wait_lock);
728
729 /*
730 * Make the actual exit decisions [12], based on the stored
731 * values.
732 *
733 * We reached the end of the lock chain. Stop right here. No
734 * point to go back just to figure that out.
735 */
736 if (!next_lock)
737 goto out_put_task;
738
739 /*
740 * If the current waiter is not the top waiter on the lock,
741 * then we can stop the chain walk here if we are not in full
742 * deadlock detection mode.
743 */
744 if (!detect_deadlock && waiter != top_waiter)
745 goto out_put_task;
746
747 goto again;
748
749 out_unlock_pi:
750 raw_spin_unlock_irq(&task->pi_lock);
751 out_put_task:
752 put_task_struct(task);
753
754 return ret;
755}
756
757/*
758 * Try to take an rt-mutex
759 *
760 * Must be called with lock->wait_lock held and interrupts disabled
761 *
762 * @lock: The lock to be acquired.
763 * @task: The task which wants to acquire the lock
764 * @waiter: The waiter that is queued to the lock's wait tree if the
765 * callsite called task_blocked_on_lock(), otherwise NULL
766 */
767static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
768 struct rt_mutex_waiter *waiter)
769{
770 /*
771 * Before testing whether we can acquire @lock, we set the
772 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
773 * other tasks which try to modify @lock into the slow path
774 * and they serialize on @lock->wait_lock.
775 *
776 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
777 * as explained at the top of this file if and only if:
778 *
779 * - There is a lock owner. The caller must fixup the
780 * transient state if it does a trylock or leaves the lock
781 * function due to a signal or timeout.
782 *
783 * - @task acquires the lock and there are no other
784 * waiters. This is undone in rt_mutex_set_owner(@task) at
785 * the end of this function.
786 */
787 mark_rt_mutex_waiters(lock);
788
789 /*
790 * If @lock has an owner, give up.
791 */
792 if (rt_mutex_owner(lock))
793 return 0;
794
795 /*
796 * If @waiter != NULL, @task has already enqueued the waiter
797 * into @lock waiter tree. If @waiter == NULL then this is a
798 * trylock attempt.
799 */
800 if (waiter) {
801 /*
802 * If waiter is not the highest priority waiter of
803 * @lock, give up.
804 */
805 if (waiter != rt_mutex_top_waiter(lock))
806 return 0;
807
808 /*
809 * We can acquire the lock. Remove the waiter from the
810 * lock waiters tree.
811 */
812 rt_mutex_dequeue(lock, waiter);
813
814 } else {
815 /*
816 * If the lock has waiters already we check whether @task is
817 * eligible to take over the lock.
818 *
819 * If there are no other waiters, @task can acquire
820 * the lock. @task->pi_blocked_on is NULL, so it does
821 * not need to be dequeued.
822 */
823 if (rt_mutex_has_waiters(lock)) {
824 /*
825 * If @task->prio is greater than or equal to
826 * the top waiter priority (kernel view),
827 * @task lost.
828 */
829 if (task->prio >= rt_mutex_top_waiter(lock)->prio)
830 return 0;
831
832 /*
833 * The current top waiter stays enqueued. We
834 * don't have to change anything in the lock
835 * waiters order.
836 */
837 } else {
838 /*
839 * No waiters. Take the lock without the
840 * pi_lock dance.@task->pi_blocked_on is NULL
841 * and we have no waiters to enqueue in @task
842 * pi waiters tree.
843 */
844 goto takeit;
845 }
846 }
847
848 /*
849 * Clear @task->pi_blocked_on. Requires protection by
850 * @task->pi_lock. Redundant operation for the @waiter == NULL
851 * case, but conditionals are more expensive than a redundant
852 * store.
853 */
854 raw_spin_lock(&task->pi_lock);
855 task->pi_blocked_on = NULL;
856 /*
857 * Finish the lock acquisition. @task is the new owner. If
858 * other waiters exist we have to insert the highest priority
859 * waiter into @task->pi_waiters tree.
860 */
861 if (rt_mutex_has_waiters(lock))
862 rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
863 raw_spin_unlock(&task->pi_lock);
864
865takeit:
866 /* We got the lock. */
867 debug_rt_mutex_lock(lock);
868
869 /*
870 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
871 * are still waiters or clears it.
872 */
873 rt_mutex_set_owner(lock, task);
874
875 rt_mutex_deadlock_account_lock(lock, task);
876
877 return 1;
878}
879
880/*
881 * Task blocks on lock.
882 *
883 * Prepare waiter and propagate pi chain
884 *
885 * This must be called with lock->wait_lock held and interrupts disabled
886 */
887static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
888 struct rt_mutex_waiter *waiter,
889 struct task_struct *task,
890 enum rtmutex_chainwalk chwalk)
891{
892 struct task_struct *owner = rt_mutex_owner(lock);
893 struct rt_mutex_waiter *top_waiter = waiter;
894 struct rt_mutex *next_lock;
895 int chain_walk = 0, res;
896
897 /*
898 * Early deadlock detection. We really don't want the task to
899 * enqueue on itself just to untangle the mess later. It's not
900 * only an optimization. We drop the locks, so another waiter
901 * can come in before the chain walk detects the deadlock. So
902 * the other will detect the deadlock and return -EDEADLOCK,
903 * which is wrong, as the other waiter is not in a deadlock
904 * situation.
905 */
906 if (owner == task)
907 return -EDEADLK;
908
909 raw_spin_lock(&task->pi_lock);
910 __rt_mutex_adjust_prio(task);
911 waiter->task = task;
912 waiter->lock = lock;
913 waiter->prio = task->prio;
914
915 /* Get the top priority waiter on the lock */
916 if (rt_mutex_has_waiters(lock))
917 top_waiter = rt_mutex_top_waiter(lock);
918 rt_mutex_enqueue(lock, waiter);
919
920 task->pi_blocked_on = waiter;
921
922 raw_spin_unlock(&task->pi_lock);
923
924 if (!owner)
925 return 0;
926
927 raw_spin_lock(&owner->pi_lock);
928 if (waiter == rt_mutex_top_waiter(lock)) {
929 rt_mutex_dequeue_pi(owner, top_waiter);
930 rt_mutex_enqueue_pi(owner, waiter);
931
932 __rt_mutex_adjust_prio(owner);
933 if (owner->pi_blocked_on)
934 chain_walk = 1;
935 } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
936 chain_walk = 1;
937 }
938
939 /* Store the lock on which owner is blocked or NULL */
940 next_lock = task_blocked_on_lock(owner);
941
942 raw_spin_unlock(&owner->pi_lock);
943 /*
944 * Even if full deadlock detection is on, if the owner is not
945 * blocked itself, we can avoid finding this out in the chain
946 * walk.
947 */
948 if (!chain_walk || !next_lock)
949 return 0;
950
951 /*
952 * The owner can't disappear while holding a lock,
953 * so the owner struct is protected by wait_lock.
954 * Gets dropped in rt_mutex_adjust_prio_chain()!
955 */
956 get_task_struct(owner);
957
958 raw_spin_unlock_irq(&lock->wait_lock);
959
960 res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
961 next_lock, waiter, task);
962
963 raw_spin_lock_irq(&lock->wait_lock);
964
965 return res;
966}
967
968/*
969 * Remove the top waiter from the current tasks pi waiter tree and
970 * queue it up.
971 *
972 * Called with lock->wait_lock held and interrupts disabled.
973 */
974static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
975 struct rt_mutex *lock)
976{
977 struct rt_mutex_waiter *waiter;
978
979 raw_spin_lock(¤t->pi_lock);
980
981 waiter = rt_mutex_top_waiter(lock);
982
983 /*
984 * Remove it from current->pi_waiters. We do not adjust a
985 * possible priority boost right now. We execute wakeup in the
986 * boosted mode and go back to normal after releasing
987 * lock->wait_lock.
988 */
989 rt_mutex_dequeue_pi(current, waiter);
990
991 /*
992 * As we are waking up the top waiter, and the waiter stays
993 * queued on the lock until it gets the lock, this lock
994 * obviously has waiters. Just set the bit here and this has
995 * the added benefit of forcing all new tasks into the
996 * slow path making sure no task of lower priority than
997 * the top waiter can steal this lock.
998 */
999 lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1000
1001 raw_spin_unlock(¤t->pi_lock);
1002
1003 wake_q_add(wake_q, waiter->task);
1004}
1005
1006/*
1007 * Remove a waiter from a lock and give up
1008 *
1009 * Must be called with lock->wait_lock held and interrupts disabled. I must
1010 * have just failed to try_to_take_rt_mutex().
1011 */
1012static void remove_waiter(struct rt_mutex *lock,
1013 struct rt_mutex_waiter *waiter)
1014{
1015 bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1016 struct task_struct *owner = rt_mutex_owner(lock);
1017 struct rt_mutex *next_lock;
1018
1019 raw_spin_lock(¤t->pi_lock);
1020 rt_mutex_dequeue(lock, waiter);
1021 current->pi_blocked_on = NULL;
1022 raw_spin_unlock(¤t->pi_lock);
1023
1024 /*
1025 * Only update priority if the waiter was the highest priority
1026 * waiter of the lock and there is an owner to update.
1027 */
1028 if (!owner || !is_top_waiter)
1029 return;
1030
1031 raw_spin_lock(&owner->pi_lock);
1032
1033 rt_mutex_dequeue_pi(owner, waiter);
1034
1035 if (rt_mutex_has_waiters(lock))
1036 rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1037
1038 __rt_mutex_adjust_prio(owner);
1039
1040 /* Store the lock on which owner is blocked or NULL */
1041 next_lock = task_blocked_on_lock(owner);
1042
1043 raw_spin_unlock(&owner->pi_lock);
1044
1045 /*
1046 * Don't walk the chain, if the owner task is not blocked
1047 * itself.
1048 */
1049 if (!next_lock)
1050 return;
1051
1052 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1053 get_task_struct(owner);
1054
1055 raw_spin_unlock_irq(&lock->wait_lock);
1056
1057 rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1058 next_lock, NULL, current);
1059
1060 raw_spin_lock_irq(&lock->wait_lock);
1061}
1062
1063/*
1064 * Recheck the pi chain, in case we got a priority setting
1065 *
1066 * Called from sched_setscheduler
1067 */
1068void rt_mutex_adjust_pi(struct task_struct *task)
1069{
1070 struct rt_mutex_waiter *waiter;
1071 struct rt_mutex *next_lock;
1072 unsigned long flags;
1073
1074 raw_spin_lock_irqsave(&task->pi_lock, flags);
1075
1076 waiter = task->pi_blocked_on;
1077 if (!waiter || (waiter->prio == task->prio &&
1078 !dl_prio(task->prio))) {
1079 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1080 return;
1081 }
1082 next_lock = waiter->lock;
1083 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1084
1085 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1086 get_task_struct(task);
1087
1088 rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1089 next_lock, NULL, task);
1090}
1091
1092/**
1093 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
1094 * @lock: the rt_mutex to take
1095 * @state: the state the task should block in (TASK_INTERRUPTIBLE
1096 * or TASK_UNINTERRUPTIBLE)
1097 * @timeout: the pre-initialized and started timer, or NULL for none
1098 * @waiter: the pre-initialized rt_mutex_waiter
1099 *
1100 * Must be called with lock->wait_lock held and interrupts disabled
1101 */
1102static int __sched
1103__rt_mutex_slowlock(struct rt_mutex *lock, int state,
1104 struct hrtimer_sleeper *timeout,
1105 struct rt_mutex_waiter *waiter)
1106{
1107 int ret = 0;
1108
1109 for (;;) {
1110 /* Try to acquire the lock: */
1111 if (try_to_take_rt_mutex(lock, current, waiter))
1112 break;
1113
1114 /*
1115 * TASK_INTERRUPTIBLE checks for signals and
1116 * timeout. Ignored otherwise.
1117 */
1118 if (unlikely(state == TASK_INTERRUPTIBLE)) {
1119 /* Signal pending? */
1120 if (signal_pending(current))
1121 ret = -EINTR;
1122 if (timeout && !timeout->task)
1123 ret = -ETIMEDOUT;
1124 if (ret)
1125 break;
1126 }
1127
1128 raw_spin_unlock_irq(&lock->wait_lock);
1129
1130 debug_rt_mutex_print_deadlock(waiter);
1131
1132 schedule();
1133
1134 raw_spin_lock_irq(&lock->wait_lock);
1135 set_current_state(state);
1136 }
1137
1138 __set_current_state(TASK_RUNNING);
1139 return ret;
1140}
1141
1142static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
1143 struct rt_mutex_waiter *w)
1144{
1145 /*
1146 * If the result is not -EDEADLOCK or the caller requested
1147 * deadlock detection, nothing to do here.
1148 */
1149 if (res != -EDEADLOCK || detect_deadlock)
1150 return;
1151
1152 /*
1153 * Yell lowdly and stop the task right here.
1154 */
1155 rt_mutex_print_deadlock(w);
1156 while (1) {
1157 set_current_state(TASK_INTERRUPTIBLE);
1158 schedule();
1159 }
1160}
1161
1162/*
1163 * Slow path lock function:
1164 */
1165static int __sched
1166rt_mutex_slowlock(struct rt_mutex *lock, int state,
1167 struct hrtimer_sleeper *timeout,
1168 enum rtmutex_chainwalk chwalk)
1169{
1170 struct rt_mutex_waiter waiter;
1171 unsigned long flags;
1172 int ret = 0;
1173
1174 debug_rt_mutex_init_waiter(&waiter);
1175 RB_CLEAR_NODE(&waiter.pi_tree_entry);
1176 RB_CLEAR_NODE(&waiter.tree_entry);
1177
1178 /*
1179 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1180 * be called in early boot if the cmpxchg() fast path is disabled
1181 * (debug, no architecture support). In this case we will acquire the
1182 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1183 * enable interrupts in that early boot case. So we need to use the
1184 * irqsave/restore variants.
1185 */
1186 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1187
1188 /* Try to acquire the lock again: */
1189 if (try_to_take_rt_mutex(lock, current, NULL)) {
1190 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1191 return 0;
1192 }
1193
1194 set_current_state(state);
1195
1196 /* Setup the timer, when timeout != NULL */
1197 if (unlikely(timeout))
1198 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1199
1200 ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1201
1202 if (likely(!ret))
1203 /* sleep on the mutex */
1204 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1205
1206 if (unlikely(ret)) {
1207 __set_current_state(TASK_RUNNING);
1208 if (rt_mutex_has_waiters(lock))
1209 remove_waiter(lock, &waiter);
1210 rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1211 }
1212
1213 /*
1214 * try_to_take_rt_mutex() sets the waiter bit
1215 * unconditionally. We might have to fix that up.
1216 */
1217 fixup_rt_mutex_waiters(lock);
1218
1219 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1220
1221 /* Remove pending timer: */
1222 if (unlikely(timeout))
1223 hrtimer_cancel(&timeout->timer);
1224
1225 debug_rt_mutex_free_waiter(&waiter);
1226
1227 return ret;
1228}
1229
1230/*
1231 * Slow path try-lock function:
1232 */
1233static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1234{
1235 unsigned long flags;
1236 int ret;
1237
1238 /*
1239 * If the lock already has an owner we fail to get the lock.
1240 * This can be done without taking the @lock->wait_lock as
1241 * it is only being read, and this is a trylock anyway.
1242 */
1243 if (rt_mutex_owner(lock))
1244 return 0;
1245
1246 /*
1247 * The mutex has currently no owner. Lock the wait lock and try to
1248 * acquire the lock. We use irqsave here to support early boot calls.
1249 */
1250 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1251
1252 ret = try_to_take_rt_mutex(lock, current, NULL);
1253
1254 /*
1255 * try_to_take_rt_mutex() sets the lock waiters bit
1256 * unconditionally. Clean this up.
1257 */
1258 fixup_rt_mutex_waiters(lock);
1259
1260 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1261
1262 return ret;
1263}
1264
1265/*
1266 * Slow path to release a rt-mutex.
1267 * Return whether the current task needs to undo a potential priority boosting.
1268 */
1269static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1270 struct wake_q_head *wake_q)
1271{
1272 unsigned long flags;
1273
1274 /* irqsave required to support early boot calls */
1275 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1276
1277 debug_rt_mutex_unlock(lock);
1278
1279 rt_mutex_deadlock_account_unlock(current);
1280
1281 /*
1282 * We must be careful here if the fast path is enabled. If we
1283 * have no waiters queued we cannot set owner to NULL here
1284 * because of:
1285 *
1286 * foo->lock->owner = NULL;
1287 * rtmutex_lock(foo->lock); <- fast path
1288 * free = atomic_dec_and_test(foo->refcnt);
1289 * rtmutex_unlock(foo->lock); <- fast path
1290 * if (free)
1291 * kfree(foo);
1292 * raw_spin_unlock(foo->lock->wait_lock);
1293 *
1294 * So for the fastpath enabled kernel:
1295 *
1296 * Nothing can set the waiters bit as long as we hold
1297 * lock->wait_lock. So we do the following sequence:
1298 *
1299 * owner = rt_mutex_owner(lock);
1300 * clear_rt_mutex_waiters(lock);
1301 * raw_spin_unlock(&lock->wait_lock);
1302 * if (cmpxchg(&lock->owner, owner, 0) == owner)
1303 * return;
1304 * goto retry;
1305 *
1306 * The fastpath disabled variant is simple as all access to
1307 * lock->owner is serialized by lock->wait_lock:
1308 *
1309 * lock->owner = NULL;
1310 * raw_spin_unlock(&lock->wait_lock);
1311 */
1312 while (!rt_mutex_has_waiters(lock)) {
1313 /* Drops lock->wait_lock ! */
1314 if (unlock_rt_mutex_safe(lock, flags) == true)
1315 return false;
1316 /* Relock the rtmutex and try again */
1317 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1318 }
1319
1320 /*
1321 * The wakeup next waiter path does not suffer from the above
1322 * race. See the comments there.
1323 *
1324 * Queue the next waiter for wakeup once we release the wait_lock.
1325 */
1326 mark_wakeup_next_waiter(wake_q, lock);
1327
1328 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1329
1330 /* check PI boosting */
1331 return true;
1332}
1333
1334/*
1335 * debug aware fast / slowpath lock,trylock,unlock
1336 *
1337 * The atomic acquire/release ops are compiled away, when either the
1338 * architecture does not support cmpxchg or when debugging is enabled.
1339 */
1340static inline int
1341rt_mutex_fastlock(struct rt_mutex *lock, int state,
1342 int (*slowfn)(struct rt_mutex *lock, int state,
1343 struct hrtimer_sleeper *timeout,
1344 enum rtmutex_chainwalk chwalk))
1345{
1346 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1347 rt_mutex_deadlock_account_lock(lock, current);
1348 return 0;
1349 } else
1350 return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1351}
1352
1353static inline int
1354rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1355 struct hrtimer_sleeper *timeout,
1356 enum rtmutex_chainwalk chwalk,
1357 int (*slowfn)(struct rt_mutex *lock, int state,
1358 struct hrtimer_sleeper *timeout,
1359 enum rtmutex_chainwalk chwalk))
1360{
1361 if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1362 likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1363 rt_mutex_deadlock_account_lock(lock, current);
1364 return 0;
1365 } else
1366 return slowfn(lock, state, timeout, chwalk);
1367}
1368
1369static inline int
1370rt_mutex_fasttrylock(struct rt_mutex *lock,
1371 int (*slowfn)(struct rt_mutex *lock))
1372{
1373 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1374 rt_mutex_deadlock_account_lock(lock, current);
1375 return 1;
1376 }
1377 return slowfn(lock);
1378}
1379
1380static inline void
1381rt_mutex_fastunlock(struct rt_mutex *lock,
1382 bool (*slowfn)(struct rt_mutex *lock,
1383 struct wake_q_head *wqh))
1384{
1385 WAKE_Q(wake_q);
1386
1387 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) {
1388 rt_mutex_deadlock_account_unlock(current);
1389
1390 } else {
1391 bool deboost = slowfn(lock, &wake_q);
1392
1393 wake_up_q(&wake_q);
1394
1395 /* Undo pi boosting if necessary: */
1396 if (deboost)
1397 rt_mutex_adjust_prio(current);
1398 }
1399}
1400
1401/**
1402 * rt_mutex_lock - lock a rt_mutex
1403 *
1404 * @lock: the rt_mutex to be locked
1405 */
1406void __sched rt_mutex_lock(struct rt_mutex *lock)
1407{
1408 might_sleep();
1409
1410 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1411}
1412EXPORT_SYMBOL_GPL(rt_mutex_lock);
1413
1414/**
1415 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1416 *
1417 * @lock: the rt_mutex to be locked
1418 *
1419 * Returns:
1420 * 0 on success
1421 * -EINTR when interrupted by a signal
1422 */
1423int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1424{
1425 might_sleep();
1426
1427 return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1428}
1429EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1430
1431/*
1432 * Futex variant with full deadlock detection.
1433 */
1434int rt_mutex_timed_futex_lock(struct rt_mutex *lock,
1435 struct hrtimer_sleeper *timeout)
1436{
1437 might_sleep();
1438
1439 return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1440 RT_MUTEX_FULL_CHAINWALK,
1441 rt_mutex_slowlock);
1442}
1443
1444/**
1445 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1446 * the timeout structure is provided
1447 * by the caller
1448 *
1449 * @lock: the rt_mutex to be locked
1450 * @timeout: timeout structure or NULL (no timeout)
1451 *
1452 * Returns:
1453 * 0 on success
1454 * -EINTR when interrupted by a signal
1455 * -ETIMEDOUT when the timeout expired
1456 */
1457int
1458rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1459{
1460 might_sleep();
1461
1462 return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1463 RT_MUTEX_MIN_CHAINWALK,
1464 rt_mutex_slowlock);
1465}
1466EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1467
1468/**
1469 * rt_mutex_trylock - try to lock a rt_mutex
1470 *
1471 * @lock: the rt_mutex to be locked
1472 *
1473 * This function can only be called in thread context. It's safe to
1474 * call it from atomic regions, but not from hard interrupt or soft
1475 * interrupt context.
1476 *
1477 * Returns 1 on success and 0 on contention
1478 */
1479int __sched rt_mutex_trylock(struct rt_mutex *lock)
1480{
1481 if (WARN_ON(in_irq() || in_nmi() || in_serving_softirq()))
1482 return 0;
1483
1484 return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1485}
1486EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1487
1488/**
1489 * rt_mutex_unlock - unlock a rt_mutex
1490 *
1491 * @lock: the rt_mutex to be unlocked
1492 */
1493void __sched rt_mutex_unlock(struct rt_mutex *lock)
1494{
1495 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1496}
1497EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1498
1499/**
1500 * rt_mutex_futex_unlock - Futex variant of rt_mutex_unlock
1501 * @lock: the rt_mutex to be unlocked
1502 *
1503 * Returns: true/false indicating whether priority adjustment is
1504 * required or not.
1505 */
1506bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock,
1507 struct wake_q_head *wqh)
1508{
1509 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) {
1510 rt_mutex_deadlock_account_unlock(current);
1511 return false;
1512 }
1513 return rt_mutex_slowunlock(lock, wqh);
1514}
1515
1516/**
1517 * rt_mutex_destroy - mark a mutex unusable
1518 * @lock: the mutex to be destroyed
1519 *
1520 * This function marks the mutex uninitialized, and any subsequent
1521 * use of the mutex is forbidden. The mutex must not be locked when
1522 * this function is called.
1523 */
1524void rt_mutex_destroy(struct rt_mutex *lock)
1525{
1526 WARN_ON(rt_mutex_is_locked(lock));
1527#ifdef CONFIG_DEBUG_RT_MUTEXES
1528 lock->magic = NULL;
1529#endif
1530}
1531
1532EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1533
1534/**
1535 * __rt_mutex_init - initialize the rt lock
1536 *
1537 * @lock: the rt lock to be initialized
1538 *
1539 * Initialize the rt lock to unlocked state.
1540 *
1541 * Initializing of a locked rt lock is not allowed
1542 */
1543void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1544{
1545 lock->owner = NULL;
1546 raw_spin_lock_init(&lock->wait_lock);
1547 lock->waiters = RB_ROOT;
1548 lock->waiters_leftmost = NULL;
1549
1550 debug_rt_mutex_init(lock, name);
1551}
1552EXPORT_SYMBOL_GPL(__rt_mutex_init);
1553
1554/**
1555 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1556 * proxy owner
1557 *
1558 * @lock: the rt_mutex to be locked
1559 * @proxy_owner:the task to set as owner
1560 *
1561 * No locking. Caller has to do serializing itself
1562 * Special API call for PI-futex support
1563 */
1564void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1565 struct task_struct *proxy_owner)
1566{
1567 __rt_mutex_init(lock, NULL);
1568 debug_rt_mutex_proxy_lock(lock, proxy_owner);
1569 rt_mutex_set_owner(lock, proxy_owner);
1570 rt_mutex_deadlock_account_lock(lock, proxy_owner);
1571}
1572
1573/**
1574 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1575 *
1576 * @lock: the rt_mutex to be locked
1577 *
1578 * No locking. Caller has to do serializing itself
1579 * Special API call for PI-futex support
1580 */
1581void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1582 struct task_struct *proxy_owner)
1583{
1584 debug_rt_mutex_proxy_unlock(lock);
1585 rt_mutex_set_owner(lock, NULL);
1586 rt_mutex_deadlock_account_unlock(proxy_owner);
1587}
1588
1589/**
1590 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1591 * @lock: the rt_mutex to take
1592 * @waiter: the pre-initialized rt_mutex_waiter
1593 * @task: the task to prepare
1594 *
1595 * Returns:
1596 * 0 - task blocked on lock
1597 * 1 - acquired the lock for task, caller should wake it up
1598 * <0 - error
1599 *
1600 * Special API call for FUTEX_REQUEUE_PI support.
1601 */
1602int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1603 struct rt_mutex_waiter *waiter,
1604 struct task_struct *task)
1605{
1606 int ret;
1607
1608 raw_spin_lock_irq(&lock->wait_lock);
1609
1610 if (try_to_take_rt_mutex(lock, task, NULL)) {
1611 raw_spin_unlock_irq(&lock->wait_lock);
1612 return 1;
1613 }
1614
1615 /* We enforce deadlock detection for futexes */
1616 ret = task_blocks_on_rt_mutex(lock, waiter, task,
1617 RT_MUTEX_FULL_CHAINWALK);
1618
1619 if (ret && !rt_mutex_owner(lock)) {
1620 /*
1621 * Reset the return value. We might have
1622 * returned with -EDEADLK and the owner
1623 * released the lock while we were walking the
1624 * pi chain. Let the waiter sort it out.
1625 */
1626 ret = 0;
1627 }
1628
1629 if (unlikely(ret))
1630 remove_waiter(lock, waiter);
1631
1632 raw_spin_unlock_irq(&lock->wait_lock);
1633
1634 debug_rt_mutex_print_deadlock(waiter);
1635
1636 return ret;
1637}
1638
1639/**
1640 * rt_mutex_next_owner - return the next owner of the lock
1641 *
1642 * @lock: the rt lock query
1643 *
1644 * Returns the next owner of the lock or NULL
1645 *
1646 * Caller has to serialize against other accessors to the lock
1647 * itself.
1648 *
1649 * Special API call for PI-futex support
1650 */
1651struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1652{
1653 if (!rt_mutex_has_waiters(lock))
1654 return NULL;
1655
1656 return rt_mutex_top_waiter(lock)->task;
1657}
1658
1659/**
1660 * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1661 * @lock: the rt_mutex we were woken on
1662 * @to: the timeout, null if none. hrtimer should already have
1663 * been started.
1664 * @waiter: the pre-initialized rt_mutex_waiter
1665 *
1666 * Complete the lock acquisition started our behalf by another thread.
1667 *
1668 * Returns:
1669 * 0 - success
1670 * <0 - error, one of -EINTR, -ETIMEDOUT
1671 *
1672 * Special API call for PI-futex requeue support
1673 */
1674int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1675 struct hrtimer_sleeper *to,
1676 struct rt_mutex_waiter *waiter)
1677{
1678 int ret;
1679
1680 raw_spin_lock_irq(&lock->wait_lock);
1681
1682 set_current_state(TASK_INTERRUPTIBLE);
1683
1684 /* sleep on the mutex */
1685 ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1686
1687 if (unlikely(ret))
1688 remove_waiter(lock, waiter);
1689
1690 /*
1691 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1692 * have to fix that up.
1693 */
1694 fixup_rt_mutex_waiters(lock);
1695
1696 raw_spin_unlock_irq(&lock->wait_lock);
1697
1698 return ret;
1699}