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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 unsigned long owner, *p = (unsigned long *) &lock->owner;
69
70 if (rt_mutex_has_waiters(lock))
71 return;
72
73 /*
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:
77 *
78 * CPU 0 CPU 1 CPU2
79 * l->owner=T1
80 * rt_mutex_lock(l)
81 * lock(l->lock)
82 * l->owner = T1 | HAS_WAITERS;
83 * enqueue(T2)
84 * boost()
85 * unlock(l->lock)
86 * block()
87 *
88 * rt_mutex_lock(l)
89 * lock(l->lock)
90 * l->owner = T1 | HAS_WAITERS;
91 * enqueue(T3)
92 * boost()
93 * unlock(l->lock)
94 * block()
95 * signal(->T2) signal(->T3)
96 * lock(l->lock)
97 * dequeue(T2)
98 * deboost()
99 * unlock(l->lock)
100 * lock(l->lock)
101 * dequeue(T3)
102 * ==> wait list is empty
103 * deboost()
104 * unlock(l->lock)
105 * lock(l->lock)
106 * fixup_rt_mutex_waiters()
107 * if (wait_list_empty(l) {
108 * l->owner = owner
109 * owner = l->owner & ~HAS_WAITERS;
110 * ==> l->owner = T1
111 * }
112 * lock(l->lock)
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)
118 *
119 * l->owner = owner
120 * ==> l->owner = T1
121 * }
122 *
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
129 * still set.
130 */
131 owner = READ_ONCE(*p);
132 if (owner & RT_MUTEX_HAS_WAITERS)
133 WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
134}
135
136/*
137 * We can speed up the acquire/release, if there's no debugging state to be
138 * set up.
139 */
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)
144
145/*
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.
149 */
150static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
151{
152 unsigned long owner, *p = (unsigned long *) &lock->owner;
153
154 do {
155 owner = *p;
156 } while (cmpxchg_relaxed(p, owner,
157 owner | RT_MUTEX_HAS_WAITERS) != owner);
158}
159
160/*
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
165 */
166static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
167 unsigned long flags)
168 __releases(lock->wait_lock)
169{
170 struct task_struct *owner = rt_mutex_owner(lock);
171
172 clear_rt_mutex_waiters(lock);
173 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
174 /*
175 * If a new waiter comes in between the unlock and the cmpxchg
176 * we have two situations:
177 *
178 * unlock(wait_lock);
179 * lock(wait_lock);
180 * cmpxchg(p, owner, 0) == owner
181 * mark_rt_mutex_waiters(lock);
182 * acquire(lock);
183 * or:
184 *
185 * unlock(wait_lock);
186 * lock(wait_lock);
187 * mark_rt_mutex_waiters(lock);
188 *
189 * cmpxchg(p, owner, 0) != owner
190 * enqueue_waiter();
191 * unlock(wait_lock);
192 * lock(wait_lock);
193 * wake waiter();
194 * unlock(wait_lock);
195 * lock(wait_lock);
196 * acquire(lock);
197 */
198 return rt_mutex_cmpxchg_release(lock, owner, NULL);
199}
200
201#else
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)
205
206static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
207{
208 lock->owner = (struct task_struct *)
209 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
210}
211
212/*
213 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
214 */
215static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
216 unsigned long flags)
217 __releases(lock->wait_lock)
218{
219 lock->owner = NULL;
220 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
221 return true;
222}
223#endif
224
225static inline int
226rt_mutex_waiter_less(struct rt_mutex_waiter *left,
227 struct rt_mutex_waiter *right)
228{
229 if (left->prio < right->prio)
230 return 1;
231
232 /*
233 * If both waiters have dl_prio(), we check the deadlines of the
234 * associated tasks.
235 * If left waiter has a dl_prio(), and we didn't return 1 above,
236 * then right waiter has a dl_prio() too.
237 */
238 if (dl_prio(left->prio))
239 return dl_time_before(left->task->dl.deadline,
240 right->task->dl.deadline);
241
242 return 0;
243}
244
245static void
246rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
247{
248 struct rb_node **link = &lock->waiters.rb_node;
249 struct rb_node *parent = NULL;
250 struct rt_mutex_waiter *entry;
251 int leftmost = 1;
252
253 while (*link) {
254 parent = *link;
255 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
256 if (rt_mutex_waiter_less(waiter, entry)) {
257 link = &parent->rb_left;
258 } else {
259 link = &parent->rb_right;
260 leftmost = 0;
261 }
262 }
263
264 if (leftmost)
265 lock->waiters_leftmost = &waiter->tree_entry;
266
267 rb_link_node(&waiter->tree_entry, parent, link);
268 rb_insert_color(&waiter->tree_entry, &lock->waiters);
269}
270
271static void
272rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
273{
274 if (RB_EMPTY_NODE(&waiter->tree_entry))
275 return;
276
277 if (lock->waiters_leftmost == &waiter->tree_entry)
278 lock->waiters_leftmost = rb_next(&waiter->tree_entry);
279
280 rb_erase(&waiter->tree_entry, &lock->waiters);
281 RB_CLEAR_NODE(&waiter->tree_entry);
282}
283
284static void
285rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
286{
287 struct rb_node **link = &task->pi_waiters.rb_node;
288 struct rb_node *parent = NULL;
289 struct rt_mutex_waiter *entry;
290 int leftmost = 1;
291
292 while (*link) {
293 parent = *link;
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;
297 } else {
298 link = &parent->rb_right;
299 leftmost = 0;
300 }
301 }
302
303 if (leftmost)
304 task->pi_waiters_leftmost = &waiter->pi_tree_entry;
305
306 rb_link_node(&waiter->pi_tree_entry, parent, link);
307 rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
308}
309
310static void
311rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
312{
313 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
314 return;
315
316 if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
317 task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
318
319 rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
320 RB_CLEAR_NODE(&waiter->pi_tree_entry);
321}
322
323/*
324 * Calculate task priority from the waiter tree priority
325 *
326 * Return task->normal_prio when the waiter tree is empty or when
327 * the waiter is not allowed to do priority boosting
328 */
329int rt_mutex_getprio(struct task_struct *task)
330{
331 if (likely(!task_has_pi_waiters(task)))
332 return task->normal_prio;
333
334 return min(task_top_pi_waiter(task)->prio,
335 task->normal_prio);
336}
337
338struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
339{
340 if (likely(!task_has_pi_waiters(task)))
341 return NULL;
342
343 return task_top_pi_waiter(task)->task;
344}
345
346/*
347 * Called by sched_setscheduler() to get the priority which will be
348 * effective after the change.
349 */
350int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
351{
352 if (!task_has_pi_waiters(task))
353 return newprio;
354
355 if (task_top_pi_waiter(task)->task->prio <= newprio)
356 return task_top_pi_waiter(task)->task->prio;
357 return newprio;
358}
359
360/*
361 * Adjust the priority of a task, after its pi_waiters got modified.
362 *
363 * This can be both boosting and unboosting. task->pi_lock must be held.
364 */
365static void __rt_mutex_adjust_prio(struct task_struct *task)
366{
367 int prio = rt_mutex_getprio(task);
368
369 if (task->prio != prio || dl_prio(prio))
370 rt_mutex_setprio(task, prio);
371}
372
373/*
374 * Adjust task priority (undo boosting). Called from the exit path of
375 * rt_mutex_slowunlock() and rt_mutex_slowlock().
376 *
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.)
381 */
382void rt_mutex_adjust_prio(struct task_struct *task)
383{
384 unsigned long flags;
385
386 raw_spin_lock_irqsave(&task->pi_lock, flags);
387 __rt_mutex_adjust_prio(task);
388 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
389}
390
391/*
392 * Deadlock detection is conditional:
393 *
394 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
395 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
396 *
397 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
398 * conducted independent of the detect argument.
399 *
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.
403 */
404static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
405 enum rtmutex_chainwalk chwalk)
406{
407 /*
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.
413 */
414 return debug_rt_mutex_detect_deadlock(waiter, chwalk);
415}
416
417/*
418 * Max number of times we'll walk the boosting chain:
419 */
420int max_lock_depth = 1024;
421
422static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
423{
424 return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
425}
426
427/*
428 * Adjust the priority chain. Also used for deadlock detection.
429 * Decreases task's usage by one - may thus free the task.
430 *
431 * @task: the task owning the mutex (owner) for which a chain walk is
432 * probably needed
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
445 *
446 * Returns 0 or -EDEADLK.
447 *
448 * Chain walk basics and protection scope
449 *
450 * [R] refcount on task
451 * [P] task->pi_lock held
452 * [L] rtmutex->wait_lock held
453 *
454 * Step Description Protected by
455 * function arguments:
456 * @task [R]
457 * @orig_lock if != NULL @top_task is blocked on it
458 * @next_lock Unprotected. Cannot be
459 * dereferenced. Only used for
460 * comparison.
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
464 * code
465 * again:
466 * loop_sanity_check();
467 * retry:
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]
474 * goto retry;
475 * }
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]
488 * goto again;
489 */
490static 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)
496{
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;
502 bool requeue = true;
503
504 detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
505
506 /*
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.
511 */
512 again:
513 /*
514 * We limit the lock chain length for each invocation.
515 */
516 if (++depth > max_lock_depth) {
517 static int prev_max;
518
519 /*
520 * Print this only once. If the admin changes the limit,
521 * print a new message when reaching the limit again.
522 */
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));
528 }
529 put_task_struct(task);
530
531 return -EDEADLK;
532 }
533
534 /*
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
538 * locks.
539 */
540 retry:
541 /*
542 * [1] Task cannot go away as we did a get_task() before !
543 */
544 raw_spin_lock_irq(&task->pi_lock);
545
546 /*
547 * [2] Get the waiter on which @task is blocked on.
548 */
549 waiter = task->pi_blocked_on;
550
551 /*
552 * [3] check_exit_conditions_1() protected by task->pi_lock.
553 */
554
555 /*
556 * Check whether the end of the boosting chain has been
557 * reached or the state of the chain has changed while we
558 * dropped the locks.
559 */
560 if (!waiter)
561 goto out_unlock_pi;
562
563 /*
564 * Check the orig_waiter state. After we dropped the locks,
565 * the previous owner of the lock might have released the lock.
566 */
567 if (orig_waiter && !rt_mutex_owner(orig_lock))
568 goto out_unlock_pi;
569
570 /*
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
574 * on @orig_lock.
575 *
576 * We stored the lock on which @task was blocked in @next_lock,
577 * so we can detect the chain change.
578 */
579 if (next_lock != waiter->lock)
580 goto out_unlock_pi;
581
582 /*
583 * Drop out, when the task has no waiters. Note,
584 * top_waiter can be NULL, when we are in the deboosting
585 * mode!
586 */
587 if (top_waiter) {
588 if (!task_has_pi_waiters(task))
589 goto out_unlock_pi;
590 /*
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.
595 */
596 if (top_waiter != task_top_pi_waiter(task)) {
597 if (!detect_deadlock)
598 goto out_unlock_pi;
599 else
600 requeue = false;
601 }
602 }
603
604 /*
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
609 * walk.
610 */
611 if (waiter->prio == task->prio) {
612 if (!detect_deadlock)
613 goto out_unlock_pi;
614 else
615 requeue = false;
616 }
617
618 /*
619 * [4] Get the next lock
620 */
621 lock = waiter->lock;
622 /*
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
625 * operations.
626 */
627 if (!raw_spin_trylock(&lock->wait_lock)) {
628 raw_spin_unlock_irq(&task->pi_lock);
629 cpu_relax();
630 goto retry;
631 }
632
633 /*
634 * [6] check_exit_conditions_2() protected by task->pi_lock and
635 * lock->wait_lock.
636 *
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.
641 */
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);
645 ret = -EDEADLK;
646 goto out_unlock_pi;
647 }
648
649 /*
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.
654 */
655 if (!requeue) {
656 /*
657 * No requeue[7] here. Just release @task [8]
658 */
659 raw_spin_unlock(&task->pi_lock);
660 put_task_struct(task);
661
662 /*
663 * [9] check_exit_conditions_3 protected by lock->wait_lock.
664 * If there is no owner of the lock, end of chain.
665 */
666 if (!rt_mutex_owner(lock)) {
667 raw_spin_unlock_irq(&lock->wait_lock);
668 return 0;
669 }
670
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);
675
676 /*
677 * No requeue [11] here. We just do deadlock detection.
678 *
679 * [12] Store whether owner is blocked
680 * itself. Decision is made after dropping the locks
681 */
682 next_lock = task_blocked_on_lock(task);
683 /*
684 * Get the top waiter for the next iteration
685 */
686 top_waiter = rt_mutex_top_waiter(lock);
687
688 /* [13] Drop locks */
689 raw_spin_unlock(&task->pi_lock);
690 raw_spin_unlock_irq(&lock->wait_lock);
691
692 /* If owner is not blocked, end of chain. */
693 if (!next_lock)
694 goto out_put_task;
695 goto again;
696 }
697
698 /*
699 * Store the current top waiter before doing the requeue
700 * operation on @lock. We need it for the boost/deboost
701 * decision below.
702 */
703 prerequeue_top_waiter = rt_mutex_top_waiter(lock);
704
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);
709
710 /* [8] Release the task */
711 raw_spin_unlock(&task->pi_lock);
712 put_task_struct(task);
713
714 /*
715 * [9] check_exit_conditions_3 protected by lock->wait_lock.
716 *
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.
720 */
721 if (!rt_mutex_owner(lock)) {
722 /*
723 * If the requeue [7] above changed the top waiter,
724 * then we need to wake the new top waiter up to try
725 * to get the lock.
726 */
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);
730 return 0;
731 }
732
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);
737
738 /* [11] requeue the pi waiters if necessary */
739 if (waiter == rt_mutex_top_waiter(lock)) {
740 /*
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.
745 */
746 rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
747 rt_mutex_enqueue_pi(task, waiter);
748 __rt_mutex_adjust_prio(task);
749
750 } else if (prerequeue_top_waiter == waiter) {
751 /*
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
756 * of the owner.
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.
760 */
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);
765 } else {
766 /*
767 * Nothing changed. No need to do any priority
768 * adjustment.
769 */
770 }
771
772 /*
773 * [12] check_exit_conditions_4() protected by task->pi_lock
774 * and lock->wait_lock. The actual decisions are made after we
775 * dropped the locks.
776 *
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.
781 */
782 next_lock = task_blocked_on_lock(task);
783 /*
784 * Store the top waiter of @lock for the end of chain walk
785 * decision below.
786 */
787 top_waiter = rt_mutex_top_waiter(lock);
788
789 /* [13] Drop the locks */
790 raw_spin_unlock(&task->pi_lock);
791 raw_spin_unlock_irq(&lock->wait_lock);
792
793 /*
794 * Make the actual exit decisions [12], based on the stored
795 * values.
796 *
797 * We reached the end of the lock chain. Stop right here. No
798 * point to go back just to figure that out.
799 */
800 if (!next_lock)
801 goto out_put_task;
802
803 /*
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.
807 */
808 if (!detect_deadlock && waiter != top_waiter)
809 goto out_put_task;
810
811 goto again;
812
813 out_unlock_pi:
814 raw_spin_unlock_irq(&task->pi_lock);
815 out_put_task:
816 put_task_struct(task);
817
818 return ret;
819}
820
821/*
822 * Try to take an rt-mutex
823 *
824 * Must be called with lock->wait_lock held and interrupts disabled
825 *
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
830 */
831static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
832 struct rt_mutex_waiter *waiter)
833{
834 /*
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.
839 *
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:
842 *
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.
846 *
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.
850 */
851 mark_rt_mutex_waiters(lock);
852
853 /*
854 * If @lock has an owner, give up.
855 */
856 if (rt_mutex_owner(lock))
857 return 0;
858
859 /*
860 * If @waiter != NULL, @task has already enqueued the waiter
861 * into @lock waiter tree. If @waiter == NULL then this is a
862 * trylock attempt.
863 */
864 if (waiter) {
865 /*
866 * If waiter is not the highest priority waiter of
867 * @lock, give up.
868 */
869 if (waiter != rt_mutex_top_waiter(lock))
870 return 0;
871
872 /*
873 * We can acquire the lock. Remove the waiter from the
874 * lock waiters tree.
875 */
876 rt_mutex_dequeue(lock, waiter);
877
878 } else {
879 /*
880 * If the lock has waiters already we check whether @task is
881 * eligible to take over the lock.
882 *
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.
886 */
887 if (rt_mutex_has_waiters(lock)) {
888 /*
889 * If @task->prio is greater than or equal to
890 * the top waiter priority (kernel view),
891 * @task lost.
892 */
893 if (task->prio >= rt_mutex_top_waiter(lock)->prio)
894 return 0;
895
896 /*
897 * The current top waiter stays enqueued. We
898 * don't have to change anything in the lock
899 * waiters order.
900 */
901 } else {
902 /*
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
906 * pi waiters tree.
907 */
908 goto takeit;
909 }
910 }
911
912 /*
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
916 * store.
917 */
918 raw_spin_lock(&task->pi_lock);
919 task->pi_blocked_on = NULL;
920 /*
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.
924 */
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);
928
929takeit:
930 /* We got the lock. */
931 debug_rt_mutex_lock(lock);
932
933 /*
934 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
935 * are still waiters or clears it.
936 */
937 rt_mutex_set_owner(lock, task);
938
939 rt_mutex_deadlock_account_lock(lock, task);
940
941 return 1;
942}
943
944/*
945 * Task blocks on lock.
946 *
947 * Prepare waiter and propagate pi chain
948 *
949 * This must be called with lock->wait_lock held and interrupts disabled
950 */
951static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
952 struct rt_mutex_waiter *waiter,
953 struct task_struct *task,
954 enum rtmutex_chainwalk chwalk)
955{
956 struct task_struct *owner = rt_mutex_owner(lock);
957 struct rt_mutex_waiter *top_waiter = waiter;
958 struct rt_mutex *next_lock;
959 int chain_walk = 0, res;
960
961 /*
962 * Early deadlock detection. We really don't want the task to
963 * enqueue on itself just to untangle the mess later. It's not
964 * only an optimization. We drop the locks, so another waiter
965 * can come in before the chain walk detects the deadlock. So
966 * the other will detect the deadlock and return -EDEADLOCK,
967 * which is wrong, as the other waiter is not in a deadlock
968 * situation.
969 */
970 if (owner == task)
971 return -EDEADLK;
972
973 raw_spin_lock(&task->pi_lock);
974 __rt_mutex_adjust_prio(task);
975 waiter->task = task;
976 waiter->lock = lock;
977 waiter->prio = task->prio;
978
979 /* Get the top priority waiter on the lock */
980 if (rt_mutex_has_waiters(lock))
981 top_waiter = rt_mutex_top_waiter(lock);
982 rt_mutex_enqueue(lock, waiter);
983
984 task->pi_blocked_on = waiter;
985
986 raw_spin_unlock(&task->pi_lock);
987
988 if (!owner)
989 return 0;
990
991 raw_spin_lock(&owner->pi_lock);
992 if (waiter == rt_mutex_top_waiter(lock)) {
993 rt_mutex_dequeue_pi(owner, top_waiter);
994 rt_mutex_enqueue_pi(owner, waiter);
995
996 __rt_mutex_adjust_prio(owner);
997 if (owner->pi_blocked_on)
998 chain_walk = 1;
999 } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
1000 chain_walk = 1;
1001 }
1002
1003 /* Store the lock on which owner is blocked or NULL */
1004 next_lock = task_blocked_on_lock(owner);
1005
1006 raw_spin_unlock(&owner->pi_lock);
1007 /*
1008 * Even if full deadlock detection is on, if the owner is not
1009 * blocked itself, we can avoid finding this out in the chain
1010 * walk.
1011 */
1012 if (!chain_walk || !next_lock)
1013 return 0;
1014
1015 /*
1016 * The owner can't disappear while holding a lock,
1017 * so the owner struct is protected by wait_lock.
1018 * Gets dropped in rt_mutex_adjust_prio_chain()!
1019 */
1020 get_task_struct(owner);
1021
1022 raw_spin_unlock_irq(&lock->wait_lock);
1023
1024 res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1025 next_lock, waiter, task);
1026
1027 raw_spin_lock_irq(&lock->wait_lock);
1028
1029 return res;
1030}
1031
1032/*
1033 * Remove the top waiter from the current tasks pi waiter tree and
1034 * queue it up.
1035 *
1036 * Called with lock->wait_lock held and interrupts disabled.
1037 */
1038static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
1039 struct rt_mutex *lock)
1040{
1041 struct rt_mutex_waiter *waiter;
1042
1043 raw_spin_lock(¤t->pi_lock);
1044
1045 waiter = rt_mutex_top_waiter(lock);
1046
1047 /*
1048 * Remove it from current->pi_waiters. We do not adjust a
1049 * possible priority boost right now. We execute wakeup in the
1050 * boosted mode and go back to normal after releasing
1051 * lock->wait_lock.
1052 */
1053 rt_mutex_dequeue_pi(current, waiter);
1054
1055 /*
1056 * As we are waking up the top waiter, and the waiter stays
1057 * queued on the lock until it gets the lock, this lock
1058 * obviously has waiters. Just set the bit here and this has
1059 * the added benefit of forcing all new tasks into the
1060 * slow path making sure no task of lower priority than
1061 * the top waiter can steal this lock.
1062 */
1063 lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1064
1065 raw_spin_unlock(¤t->pi_lock);
1066
1067 wake_q_add(wake_q, waiter->task);
1068}
1069
1070/*
1071 * Remove a waiter from a lock and give up
1072 *
1073 * Must be called with lock->wait_lock held and interrupts disabled. I must
1074 * have just failed to try_to_take_rt_mutex().
1075 */
1076static void remove_waiter(struct rt_mutex *lock,
1077 struct rt_mutex_waiter *waiter)
1078{
1079 bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1080 struct task_struct *owner = rt_mutex_owner(lock);
1081 struct rt_mutex *next_lock;
1082
1083 raw_spin_lock(¤t->pi_lock);
1084 rt_mutex_dequeue(lock, waiter);
1085 current->pi_blocked_on = NULL;
1086 raw_spin_unlock(¤t->pi_lock);
1087
1088 /*
1089 * Only update priority if the waiter was the highest priority
1090 * waiter of the lock and there is an owner to update.
1091 */
1092 if (!owner || !is_top_waiter)
1093 return;
1094
1095 raw_spin_lock(&owner->pi_lock);
1096
1097 rt_mutex_dequeue_pi(owner, waiter);
1098
1099 if (rt_mutex_has_waiters(lock))
1100 rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1101
1102 __rt_mutex_adjust_prio(owner);
1103
1104 /* Store the lock on which owner is blocked or NULL */
1105 next_lock = task_blocked_on_lock(owner);
1106
1107 raw_spin_unlock(&owner->pi_lock);
1108
1109 /*
1110 * Don't walk the chain, if the owner task is not blocked
1111 * itself.
1112 */
1113 if (!next_lock)
1114 return;
1115
1116 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1117 get_task_struct(owner);
1118
1119 raw_spin_unlock_irq(&lock->wait_lock);
1120
1121 rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1122 next_lock, NULL, current);
1123
1124 raw_spin_lock_irq(&lock->wait_lock);
1125}
1126
1127/*
1128 * Recheck the pi chain, in case we got a priority setting
1129 *
1130 * Called from sched_setscheduler
1131 */
1132void rt_mutex_adjust_pi(struct task_struct *task)
1133{
1134 struct rt_mutex_waiter *waiter;
1135 struct rt_mutex *next_lock;
1136 unsigned long flags;
1137
1138 raw_spin_lock_irqsave(&task->pi_lock, flags);
1139
1140 waiter = task->pi_blocked_on;
1141 if (!waiter || (waiter->prio == task->prio &&
1142 !dl_prio(task->prio))) {
1143 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1144 return;
1145 }
1146 next_lock = waiter->lock;
1147 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1148
1149 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1150 get_task_struct(task);
1151
1152 rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1153 next_lock, NULL, task);
1154}
1155
1156/**
1157 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
1158 * @lock: the rt_mutex to take
1159 * @state: the state the task should block in (TASK_INTERRUPTIBLE
1160 * or TASK_UNINTERRUPTIBLE)
1161 * @timeout: the pre-initialized and started timer, or NULL for none
1162 * @waiter: the pre-initialized rt_mutex_waiter
1163 *
1164 * Must be called with lock->wait_lock held and interrupts disabled
1165 */
1166static int __sched
1167__rt_mutex_slowlock(struct rt_mutex *lock, int state,
1168 struct hrtimer_sleeper *timeout,
1169 struct rt_mutex_waiter *waiter)
1170{
1171 int ret = 0;
1172
1173 for (;;) {
1174 /* Try to acquire the lock: */
1175 if (try_to_take_rt_mutex(lock, current, waiter))
1176 break;
1177
1178 /*
1179 * TASK_INTERRUPTIBLE checks for signals and
1180 * timeout. Ignored otherwise.
1181 */
1182 if (unlikely(state == TASK_INTERRUPTIBLE)) {
1183 /* Signal pending? */
1184 if (signal_pending(current))
1185 ret = -EINTR;
1186 if (timeout && !timeout->task)
1187 ret = -ETIMEDOUT;
1188 if (ret)
1189 break;
1190 }
1191
1192 raw_spin_unlock_irq(&lock->wait_lock);
1193
1194 debug_rt_mutex_print_deadlock(waiter);
1195
1196 schedule();
1197
1198 raw_spin_lock_irq(&lock->wait_lock);
1199 set_current_state(state);
1200 }
1201
1202 __set_current_state(TASK_RUNNING);
1203 return ret;
1204}
1205
1206static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
1207 struct rt_mutex_waiter *w)
1208{
1209 /*
1210 * If the result is not -EDEADLOCK or the caller requested
1211 * deadlock detection, nothing to do here.
1212 */
1213 if (res != -EDEADLOCK || detect_deadlock)
1214 return;
1215
1216 /*
1217 * Yell lowdly and stop the task right here.
1218 */
1219 rt_mutex_print_deadlock(w);
1220 while (1) {
1221 set_current_state(TASK_INTERRUPTIBLE);
1222 schedule();
1223 }
1224}
1225
1226/*
1227 * Slow path lock function:
1228 */
1229static int __sched
1230rt_mutex_slowlock(struct rt_mutex *lock, int state,
1231 struct hrtimer_sleeper *timeout,
1232 enum rtmutex_chainwalk chwalk)
1233{
1234 struct rt_mutex_waiter waiter;
1235 unsigned long flags;
1236 int ret = 0;
1237
1238 debug_rt_mutex_init_waiter(&waiter);
1239 RB_CLEAR_NODE(&waiter.pi_tree_entry);
1240 RB_CLEAR_NODE(&waiter.tree_entry);
1241
1242 /*
1243 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1244 * be called in early boot if the cmpxchg() fast path is disabled
1245 * (debug, no architecture support). In this case we will acquire the
1246 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1247 * enable interrupts in that early boot case. So we need to use the
1248 * irqsave/restore variants.
1249 */
1250 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1251
1252 /* Try to acquire the lock again: */
1253 if (try_to_take_rt_mutex(lock, current, NULL)) {
1254 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1255 return 0;
1256 }
1257
1258 set_current_state(state);
1259
1260 /* Setup the timer, when timeout != NULL */
1261 if (unlikely(timeout))
1262 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1263
1264 ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1265
1266 if (likely(!ret))
1267 /* sleep on the mutex */
1268 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1269
1270 if (unlikely(ret)) {
1271 __set_current_state(TASK_RUNNING);
1272 if (rt_mutex_has_waiters(lock))
1273 remove_waiter(lock, &waiter);
1274 rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1275 }
1276
1277 /*
1278 * try_to_take_rt_mutex() sets the waiter bit
1279 * unconditionally. We might have to fix that up.
1280 */
1281 fixup_rt_mutex_waiters(lock);
1282
1283 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1284
1285 /* Remove pending timer: */
1286 if (unlikely(timeout))
1287 hrtimer_cancel(&timeout->timer);
1288
1289 debug_rt_mutex_free_waiter(&waiter);
1290
1291 return ret;
1292}
1293
1294/*
1295 * Slow path try-lock function:
1296 */
1297static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1298{
1299 unsigned long flags;
1300 int ret;
1301
1302 /*
1303 * If the lock already has an owner we fail to get the lock.
1304 * This can be done without taking the @lock->wait_lock as
1305 * it is only being read, and this is a trylock anyway.
1306 */
1307 if (rt_mutex_owner(lock))
1308 return 0;
1309
1310 /*
1311 * The mutex has currently no owner. Lock the wait lock and try to
1312 * acquire the lock. We use irqsave here to support early boot calls.
1313 */
1314 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1315
1316 ret = try_to_take_rt_mutex(lock, current, NULL);
1317
1318 /*
1319 * try_to_take_rt_mutex() sets the lock waiters bit
1320 * unconditionally. Clean this up.
1321 */
1322 fixup_rt_mutex_waiters(lock);
1323
1324 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1325
1326 return ret;
1327}
1328
1329/*
1330 * Slow path to release a rt-mutex.
1331 * Return whether the current task needs to undo a potential priority boosting.
1332 */
1333static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1334 struct wake_q_head *wake_q)
1335{
1336 unsigned long flags;
1337
1338 /* irqsave required to support early boot calls */
1339 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1340
1341 debug_rt_mutex_unlock(lock);
1342
1343 rt_mutex_deadlock_account_unlock(current);
1344
1345 /*
1346 * We must be careful here if the fast path is enabled. If we
1347 * have no waiters queued we cannot set owner to NULL here
1348 * because of:
1349 *
1350 * foo->lock->owner = NULL;
1351 * rtmutex_lock(foo->lock); <- fast path
1352 * free = atomic_dec_and_test(foo->refcnt);
1353 * rtmutex_unlock(foo->lock); <- fast path
1354 * if (free)
1355 * kfree(foo);
1356 * raw_spin_unlock(foo->lock->wait_lock);
1357 *
1358 * So for the fastpath enabled kernel:
1359 *
1360 * Nothing can set the waiters bit as long as we hold
1361 * lock->wait_lock. So we do the following sequence:
1362 *
1363 * owner = rt_mutex_owner(lock);
1364 * clear_rt_mutex_waiters(lock);
1365 * raw_spin_unlock(&lock->wait_lock);
1366 * if (cmpxchg(&lock->owner, owner, 0) == owner)
1367 * return;
1368 * goto retry;
1369 *
1370 * The fastpath disabled variant is simple as all access to
1371 * lock->owner is serialized by lock->wait_lock:
1372 *
1373 * lock->owner = NULL;
1374 * raw_spin_unlock(&lock->wait_lock);
1375 */
1376 while (!rt_mutex_has_waiters(lock)) {
1377 /* Drops lock->wait_lock ! */
1378 if (unlock_rt_mutex_safe(lock, flags) == true)
1379 return false;
1380 /* Relock the rtmutex and try again */
1381 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1382 }
1383
1384 /*
1385 * The wakeup next waiter path does not suffer from the above
1386 * race. See the comments there.
1387 *
1388 * Queue the next waiter for wakeup once we release the wait_lock.
1389 */
1390 mark_wakeup_next_waiter(wake_q, lock);
1391
1392 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1393
1394 /* check PI boosting */
1395 return true;
1396}
1397
1398/*
1399 * debug aware fast / slowpath lock,trylock,unlock
1400 *
1401 * The atomic acquire/release ops are compiled away, when either the
1402 * architecture does not support cmpxchg or when debugging is enabled.
1403 */
1404static inline int
1405rt_mutex_fastlock(struct rt_mutex *lock, int state,
1406 int (*slowfn)(struct rt_mutex *lock, int state,
1407 struct hrtimer_sleeper *timeout,
1408 enum rtmutex_chainwalk chwalk))
1409{
1410 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1411 rt_mutex_deadlock_account_lock(lock, current);
1412 return 0;
1413 } else
1414 return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1415}
1416
1417static inline int
1418rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1419 struct hrtimer_sleeper *timeout,
1420 enum rtmutex_chainwalk chwalk,
1421 int (*slowfn)(struct rt_mutex *lock, int state,
1422 struct hrtimer_sleeper *timeout,
1423 enum rtmutex_chainwalk chwalk))
1424{
1425 if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1426 likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1427 rt_mutex_deadlock_account_lock(lock, current);
1428 return 0;
1429 } else
1430 return slowfn(lock, state, timeout, chwalk);
1431}
1432
1433static inline int
1434rt_mutex_fasttrylock(struct rt_mutex *lock,
1435 int (*slowfn)(struct rt_mutex *lock))
1436{
1437 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current))) {
1438 rt_mutex_deadlock_account_lock(lock, current);
1439 return 1;
1440 }
1441 return slowfn(lock);
1442}
1443
1444static inline void
1445rt_mutex_fastunlock(struct rt_mutex *lock,
1446 bool (*slowfn)(struct rt_mutex *lock,
1447 struct wake_q_head *wqh))
1448{
1449 DEFINE_WAKE_Q(wake_q);
1450
1451 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) {
1452 rt_mutex_deadlock_account_unlock(current);
1453
1454 } else {
1455 bool deboost = slowfn(lock, &wake_q);
1456
1457 wake_up_q(&wake_q);
1458
1459 /* Undo pi boosting if necessary: */
1460 if (deboost)
1461 rt_mutex_adjust_prio(current);
1462 }
1463}
1464
1465/**
1466 * rt_mutex_lock - lock a rt_mutex
1467 *
1468 * @lock: the rt_mutex to be locked
1469 */
1470void __sched rt_mutex_lock(struct rt_mutex *lock)
1471{
1472 might_sleep();
1473
1474 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1475}
1476EXPORT_SYMBOL_GPL(rt_mutex_lock);
1477
1478/**
1479 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1480 *
1481 * @lock: the rt_mutex to be locked
1482 *
1483 * Returns:
1484 * 0 on success
1485 * -EINTR when interrupted by a signal
1486 */
1487int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1488{
1489 might_sleep();
1490
1491 return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1492}
1493EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1494
1495/*
1496 * Futex variant with full deadlock detection.
1497 */
1498int rt_mutex_timed_futex_lock(struct rt_mutex *lock,
1499 struct hrtimer_sleeper *timeout)
1500{
1501 might_sleep();
1502
1503 return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1504 RT_MUTEX_FULL_CHAINWALK,
1505 rt_mutex_slowlock);
1506}
1507
1508/**
1509 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1510 * the timeout structure is provided
1511 * by the caller
1512 *
1513 * @lock: the rt_mutex to be locked
1514 * @timeout: timeout structure or NULL (no timeout)
1515 *
1516 * Returns:
1517 * 0 on success
1518 * -EINTR when interrupted by a signal
1519 * -ETIMEDOUT when the timeout expired
1520 */
1521int
1522rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1523{
1524 might_sleep();
1525
1526 return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1527 RT_MUTEX_MIN_CHAINWALK,
1528 rt_mutex_slowlock);
1529}
1530EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1531
1532/**
1533 * rt_mutex_trylock - try to lock a rt_mutex
1534 *
1535 * @lock: the rt_mutex to be locked
1536 *
1537 * This function can only be called in thread context. It's safe to
1538 * call it from atomic regions, but not from hard interrupt or soft
1539 * interrupt context.
1540 *
1541 * Returns 1 on success and 0 on contention
1542 */
1543int __sched rt_mutex_trylock(struct rt_mutex *lock)
1544{
1545 if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
1546 return 0;
1547
1548 return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1549}
1550EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1551
1552/**
1553 * rt_mutex_unlock - unlock a rt_mutex
1554 *
1555 * @lock: the rt_mutex to be unlocked
1556 */
1557void __sched rt_mutex_unlock(struct rt_mutex *lock)
1558{
1559 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1560}
1561EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1562
1563/**
1564 * rt_mutex_futex_unlock - Futex variant of rt_mutex_unlock
1565 * @lock: the rt_mutex to be unlocked
1566 *
1567 * Returns: true/false indicating whether priority adjustment is
1568 * required or not.
1569 */
1570bool __sched rt_mutex_futex_unlock(struct rt_mutex *lock,
1571 struct wake_q_head *wqh)
1572{
1573 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL))) {
1574 rt_mutex_deadlock_account_unlock(current);
1575 return false;
1576 }
1577 return rt_mutex_slowunlock(lock, wqh);
1578}
1579
1580/**
1581 * rt_mutex_destroy - mark a mutex unusable
1582 * @lock: the mutex to be destroyed
1583 *
1584 * This function marks the mutex uninitialized, and any subsequent
1585 * use of the mutex is forbidden. The mutex must not be locked when
1586 * this function is called.
1587 */
1588void rt_mutex_destroy(struct rt_mutex *lock)
1589{
1590 WARN_ON(rt_mutex_is_locked(lock));
1591#ifdef CONFIG_DEBUG_RT_MUTEXES
1592 lock->magic = NULL;
1593#endif
1594}
1595
1596EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1597
1598/**
1599 * __rt_mutex_init - initialize the rt lock
1600 *
1601 * @lock: the rt lock to be initialized
1602 *
1603 * Initialize the rt lock to unlocked state.
1604 *
1605 * Initializing of a locked rt lock is not allowed
1606 */
1607void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1608{
1609 lock->owner = NULL;
1610 raw_spin_lock_init(&lock->wait_lock);
1611 lock->waiters = RB_ROOT;
1612 lock->waiters_leftmost = NULL;
1613
1614 debug_rt_mutex_init(lock, name);
1615}
1616EXPORT_SYMBOL_GPL(__rt_mutex_init);
1617
1618/**
1619 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1620 * proxy owner
1621 *
1622 * @lock: the rt_mutex to be locked
1623 * @proxy_owner:the task to set as owner
1624 *
1625 * No locking. Caller has to do serializing itself
1626 *
1627 * Special API call for PI-futex support. This initializes the rtmutex and
1628 * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
1629 * possible at this point because the pi_state which contains the rtmutex
1630 * is not yet visible to other tasks.
1631 */
1632void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1633 struct task_struct *proxy_owner)
1634{
1635 __rt_mutex_init(lock, NULL);
1636 debug_rt_mutex_proxy_lock(lock, proxy_owner);
1637 rt_mutex_set_owner(lock, proxy_owner);
1638 rt_mutex_deadlock_account_lock(lock, proxy_owner);
1639}
1640
1641/**
1642 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1643 *
1644 * @lock: the rt_mutex to be locked
1645 *
1646 * No locking. Caller has to do serializing itself
1647 *
1648 * Special API call for PI-futex support. This merrily cleans up the rtmutex
1649 * (debugging) state. Concurrent operations on this rt_mutex are not
1650 * possible because it belongs to the pi_state which is about to be freed
1651 * and it is not longer visible to other tasks.
1652 */
1653void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1654 struct task_struct *proxy_owner)
1655{
1656 debug_rt_mutex_proxy_unlock(lock);
1657 rt_mutex_set_owner(lock, NULL);
1658 rt_mutex_deadlock_account_unlock(proxy_owner);
1659}
1660
1661/**
1662 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1663 * @lock: the rt_mutex to take
1664 * @waiter: the pre-initialized rt_mutex_waiter
1665 * @task: the task to prepare
1666 *
1667 * Returns:
1668 * 0 - task blocked on lock
1669 * 1 - acquired the lock for task, caller should wake it up
1670 * <0 - error
1671 *
1672 * Special API call for FUTEX_REQUEUE_PI support.
1673 */
1674int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1675 struct rt_mutex_waiter *waiter,
1676 struct task_struct *task)
1677{
1678 int ret;
1679
1680 raw_spin_lock_irq(&lock->wait_lock);
1681
1682 if (try_to_take_rt_mutex(lock, task, NULL)) {
1683 raw_spin_unlock_irq(&lock->wait_lock);
1684 return 1;
1685 }
1686
1687 /* We enforce deadlock detection for futexes */
1688 ret = task_blocks_on_rt_mutex(lock, waiter, task,
1689 RT_MUTEX_FULL_CHAINWALK);
1690
1691 if (ret && !rt_mutex_owner(lock)) {
1692 /*
1693 * Reset the return value. We might have
1694 * returned with -EDEADLK and the owner
1695 * released the lock while we were walking the
1696 * pi chain. Let the waiter sort it out.
1697 */
1698 ret = 0;
1699 }
1700
1701 if (unlikely(ret))
1702 remove_waiter(lock, waiter);
1703
1704 raw_spin_unlock_irq(&lock->wait_lock);
1705
1706 debug_rt_mutex_print_deadlock(waiter);
1707
1708 return ret;
1709}
1710
1711/**
1712 * rt_mutex_next_owner - return the next owner of the lock
1713 *
1714 * @lock: the rt lock query
1715 *
1716 * Returns the next owner of the lock or NULL
1717 *
1718 * Caller has to serialize against other accessors to the lock
1719 * itself.
1720 *
1721 * Special API call for PI-futex support
1722 */
1723struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1724{
1725 if (!rt_mutex_has_waiters(lock))
1726 return NULL;
1727
1728 return rt_mutex_top_waiter(lock)->task;
1729}
1730
1731/**
1732 * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1733 * @lock: the rt_mutex we were woken on
1734 * @to: the timeout, null if none. hrtimer should already have
1735 * been started.
1736 * @waiter: the pre-initialized rt_mutex_waiter
1737 *
1738 * Complete the lock acquisition started our behalf by another thread.
1739 *
1740 * Returns:
1741 * 0 - success
1742 * <0 - error, one of -EINTR, -ETIMEDOUT
1743 *
1744 * Special API call for PI-futex requeue support
1745 */
1746int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1747 struct hrtimer_sleeper *to,
1748 struct rt_mutex_waiter *waiter)
1749{
1750 int ret;
1751
1752 raw_spin_lock_irq(&lock->wait_lock);
1753
1754 set_current_state(TASK_INTERRUPTIBLE);
1755
1756 /* sleep on the mutex */
1757 ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1758
1759 if (unlikely(ret))
1760 remove_waiter(lock, waiter);
1761
1762 /*
1763 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1764 * have to fix that up.
1765 */
1766 fixup_rt_mutex_waiters(lock);
1767
1768 raw_spin_unlock_irq(&lock->wait_lock);
1769
1770 return ret;
1771}