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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// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
4 *
5 * started by Ingo Molnar and Thomas Gleixner.
6 *
7 * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8 * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
9 * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
10 * Copyright (C) 2006 Esben Nielsen
11 *
12 * See Documentation/locking/rt-mutex-design.rst for details.
13 */
14#include <linux/spinlock.h>
15#include <linux/export.h>
16#include <linux/sched/signal.h>
17#include <linux/sched/rt.h>
18#include <linux/sched/deadline.h>
19#include <linux/sched/wake_q.h>
20#include <linux/sched/debug.h>
21#include <linux/timer.h>
22
23#include "rtmutex_common.h"
24
25/*
26 * lock->owner state tracking:
27 *
28 * lock->owner holds the task_struct pointer of the owner. Bit 0
29 * is used to keep track of the "lock has waiters" state.
30 *
31 * owner bit0
32 * NULL 0 lock is free (fast acquire possible)
33 * NULL 1 lock is free and has waiters and the top waiter
34 * is going to take the lock*
35 * taskpointer 0 lock is held (fast release possible)
36 * taskpointer 1 lock is held and has waiters**
37 *
38 * The fast atomic compare exchange based acquire and release is only
39 * possible when bit 0 of lock->owner is 0.
40 *
41 * (*) It also can be a transitional state when grabbing the lock
42 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
43 * we need to set the bit0 before looking at the lock, and the owner may be
44 * NULL in this small time, hence this can be a transitional state.
45 *
46 * (**) There is a small time when bit 0 is set but there are no
47 * waiters. This can happen when grabbing the lock in the slow path.
48 * To prevent a cmpxchg of the owner releasing the lock, we need to
49 * set this bit before looking at the lock.
50 */
51
52static void
53rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
54{
55 unsigned long val = (unsigned long)owner;
56
57 if (rt_mutex_has_waiters(lock))
58 val |= RT_MUTEX_HAS_WAITERS;
59
60 WRITE_ONCE(lock->owner, (struct task_struct *)val);
61}
62
63static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
64{
65 lock->owner = (struct task_struct *)
66 ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
67}
68
69static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
70{
71 unsigned long owner, *p = (unsigned long *) &lock->owner;
72
73 if (rt_mutex_has_waiters(lock))
74 return;
75
76 /*
77 * The rbtree has no waiters enqueued, now make sure that the
78 * lock->owner still has the waiters bit set, otherwise the
79 * following can happen:
80 *
81 * CPU 0 CPU 1 CPU2
82 * l->owner=T1
83 * rt_mutex_lock(l)
84 * lock(l->lock)
85 * l->owner = T1 | HAS_WAITERS;
86 * enqueue(T2)
87 * boost()
88 * unlock(l->lock)
89 * block()
90 *
91 * rt_mutex_lock(l)
92 * lock(l->lock)
93 * l->owner = T1 | HAS_WAITERS;
94 * enqueue(T3)
95 * boost()
96 * unlock(l->lock)
97 * block()
98 * signal(->T2) signal(->T3)
99 * lock(l->lock)
100 * dequeue(T2)
101 * deboost()
102 * unlock(l->lock)
103 * lock(l->lock)
104 * dequeue(T3)
105 * ==> wait list is empty
106 * deboost()
107 * unlock(l->lock)
108 * lock(l->lock)
109 * fixup_rt_mutex_waiters()
110 * if (wait_list_empty(l) {
111 * l->owner = owner
112 * owner = l->owner & ~HAS_WAITERS;
113 * ==> l->owner = T1
114 * }
115 * lock(l->lock)
116 * rt_mutex_unlock(l) fixup_rt_mutex_waiters()
117 * if (wait_list_empty(l) {
118 * owner = l->owner & ~HAS_WAITERS;
119 * cmpxchg(l->owner, T1, NULL)
120 * ===> Success (l->owner = NULL)
121 *
122 * l->owner = owner
123 * ==> l->owner = T1
124 * }
125 *
126 * With the check for the waiter bit in place T3 on CPU2 will not
127 * overwrite. All tasks fiddling with the waiters bit are
128 * serialized by l->lock, so nothing else can modify the waiters
129 * bit. If the bit is set then nothing can change l->owner either
130 * so the simple RMW is safe. The cmpxchg() will simply fail if it
131 * happens in the middle of the RMW because the waiters bit is
132 * still set.
133 */
134 owner = READ_ONCE(*p);
135 if (owner & RT_MUTEX_HAS_WAITERS)
136 WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
137}
138
139/*
140 * We can speed up the acquire/release, if there's no debugging state to be
141 * set up.
142 */
143#ifndef CONFIG_DEBUG_RT_MUTEXES
144# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
145# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
146
147/*
148 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
149 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
150 * relaxed semantics suffice.
151 */
152static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
153{
154 unsigned long owner, *p = (unsigned long *) &lock->owner;
155
156 do {
157 owner = *p;
158 } while (cmpxchg_relaxed(p, owner,
159 owner | RT_MUTEX_HAS_WAITERS) != owner);
160}
161
162/*
163 * Safe fastpath aware unlock:
164 * 1) Clear the waiters bit
165 * 2) Drop lock->wait_lock
166 * 3) Try to unlock the lock with cmpxchg
167 */
168static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
169 unsigned long flags)
170 __releases(lock->wait_lock)
171{
172 struct task_struct *owner = rt_mutex_owner(lock);
173
174 clear_rt_mutex_waiters(lock);
175 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
176 /*
177 * If a new waiter comes in between the unlock and the cmpxchg
178 * we have two situations:
179 *
180 * unlock(wait_lock);
181 * lock(wait_lock);
182 * cmpxchg(p, owner, 0) == owner
183 * mark_rt_mutex_waiters(lock);
184 * acquire(lock);
185 * or:
186 *
187 * unlock(wait_lock);
188 * lock(wait_lock);
189 * mark_rt_mutex_waiters(lock);
190 *
191 * cmpxchg(p, owner, 0) != owner
192 * enqueue_waiter();
193 * unlock(wait_lock);
194 * lock(wait_lock);
195 * wake waiter();
196 * unlock(wait_lock);
197 * lock(wait_lock);
198 * acquire(lock);
199 */
200 return rt_mutex_cmpxchg_release(lock, owner, NULL);
201}
202
203#else
204# define rt_mutex_cmpxchg_acquire(l,c,n) (0)
205# define rt_mutex_cmpxchg_release(l,c,n) (0)
206
207static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
208{
209 lock->owner = (struct task_struct *)
210 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
211}
212
213/*
214 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
215 */
216static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
217 unsigned long flags)
218 __releases(lock->wait_lock)
219{
220 lock->owner = NULL;
221 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
222 return true;
223}
224#endif
225
226/*
227 * Only use with rt_mutex_waiter_{less,equal}()
228 */
229#define task_to_waiter(p) \
230 &(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }
231
232static inline int
233rt_mutex_waiter_less(struct rt_mutex_waiter *left,
234 struct rt_mutex_waiter *right)
235{
236 if (left->prio < right->prio)
237 return 1;
238
239 /*
240 * If both waiters have dl_prio(), we check the deadlines of the
241 * associated tasks.
242 * If left waiter has a dl_prio(), and we didn't return 1 above,
243 * then right waiter has a dl_prio() too.
244 */
245 if (dl_prio(left->prio))
246 return dl_time_before(left->deadline, right->deadline);
247
248 return 0;
249}
250
251static inline int
252rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
253 struct rt_mutex_waiter *right)
254{
255 if (left->prio != right->prio)
256 return 0;
257
258 /*
259 * If both waiters have dl_prio(), we check the deadlines of the
260 * associated tasks.
261 * If left waiter has a dl_prio(), and we didn't return 0 above,
262 * then right waiter has a dl_prio() too.
263 */
264 if (dl_prio(left->prio))
265 return left->deadline == right->deadline;
266
267 return 1;
268}
269
270static void
271rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
272{
273 struct rb_node **link = &lock->waiters.rb_root.rb_node;
274 struct rb_node *parent = NULL;
275 struct rt_mutex_waiter *entry;
276 bool leftmost = true;
277
278 while (*link) {
279 parent = *link;
280 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
281 if (rt_mutex_waiter_less(waiter, entry)) {
282 link = &parent->rb_left;
283 } else {
284 link = &parent->rb_right;
285 leftmost = false;
286 }
287 }
288
289 rb_link_node(&waiter->tree_entry, parent, link);
290 rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
291}
292
293static void
294rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
295{
296 if (RB_EMPTY_NODE(&waiter->tree_entry))
297 return;
298
299 rb_erase_cached(&waiter->tree_entry, &lock->waiters);
300 RB_CLEAR_NODE(&waiter->tree_entry);
301}
302
303static void
304rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
305{
306 struct rb_node **link = &task->pi_waiters.rb_root.rb_node;
307 struct rb_node *parent = NULL;
308 struct rt_mutex_waiter *entry;
309 bool leftmost = true;
310
311 while (*link) {
312 parent = *link;
313 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
314 if (rt_mutex_waiter_less(waiter, entry)) {
315 link = &parent->rb_left;
316 } else {
317 link = &parent->rb_right;
318 leftmost = false;
319 }
320 }
321
322 rb_link_node(&waiter->pi_tree_entry, parent, link);
323 rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
324}
325
326static void
327rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
328{
329 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
330 return;
331
332 rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
333 RB_CLEAR_NODE(&waiter->pi_tree_entry);
334}
335
336static void rt_mutex_adjust_prio(struct task_struct *p)
337{
338 struct task_struct *pi_task = NULL;
339
340 lockdep_assert_held(&p->pi_lock);
341
342 if (task_has_pi_waiters(p))
343 pi_task = task_top_pi_waiter(p)->task;
344
345 rt_mutex_setprio(p, pi_task);
346}
347
348/*
349 * Deadlock detection is conditional:
350 *
351 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
352 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
353 *
354 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
355 * conducted independent of the detect argument.
356 *
357 * If the waiter argument is NULL this indicates the deboost path and
358 * deadlock detection is disabled independent of the detect argument
359 * and the config settings.
360 */
361static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
362 enum rtmutex_chainwalk chwalk)
363{
364 /*
365 * This is just a wrapper function for the following call,
366 * because debug_rt_mutex_detect_deadlock() smells like a magic
367 * debug feature and I wanted to keep the cond function in the
368 * main source file along with the comments instead of having
369 * two of the same in the headers.
370 */
371 return debug_rt_mutex_detect_deadlock(waiter, chwalk);
372}
373
374/*
375 * Max number of times we'll walk the boosting chain:
376 */
377int max_lock_depth = 1024;
378
379static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
380{
381 return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
382}
383
384/*
385 * Adjust the priority chain. Also used for deadlock detection.
386 * Decreases task's usage by one - may thus free the task.
387 *
388 * @task: the task owning the mutex (owner) for which a chain walk is
389 * probably needed
390 * @chwalk: do we have to carry out deadlock detection?
391 * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
392 * things for a task that has just got its priority adjusted, and
393 * is waiting on a mutex)
394 * @next_lock: the mutex on which the owner of @orig_lock was blocked before
395 * we dropped its pi_lock. Is never dereferenced, only used for
396 * comparison to detect lock chain changes.
397 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
398 * its priority to the mutex owner (can be NULL in the case
399 * depicted above or if the top waiter is gone away and we are
400 * actually deboosting the owner)
401 * @top_task: the current top waiter
402 *
403 * Returns 0 or -EDEADLK.
404 *
405 * Chain walk basics and protection scope
406 *
407 * [R] refcount on task
408 * [P] task->pi_lock held
409 * [L] rtmutex->wait_lock held
410 *
411 * Step Description Protected by
412 * function arguments:
413 * @task [R]
414 * @orig_lock if != NULL @top_task is blocked on it
415 * @next_lock Unprotected. Cannot be
416 * dereferenced. Only used for
417 * comparison.
418 * @orig_waiter if != NULL @top_task is blocked on it
419 * @top_task current, or in case of proxy
420 * locking protected by calling
421 * code
422 * again:
423 * loop_sanity_check();
424 * retry:
425 * [1] lock(task->pi_lock); [R] acquire [P]
426 * [2] waiter = task->pi_blocked_on; [P]
427 * [3] check_exit_conditions_1(); [P]
428 * [4] lock = waiter->lock; [P]
429 * [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
430 * unlock(task->pi_lock); release [P]
431 * goto retry;
432 * }
433 * [6] check_exit_conditions_2(); [P] + [L]
434 * [7] requeue_lock_waiter(lock, waiter); [P] + [L]
435 * [8] unlock(task->pi_lock); release [P]
436 * put_task_struct(task); release [R]
437 * [9] check_exit_conditions_3(); [L]
438 * [10] task = owner(lock); [L]
439 * get_task_struct(task); [L] acquire [R]
440 * lock(task->pi_lock); [L] acquire [P]
441 * [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
442 * [12] check_exit_conditions_4(); [P] + [L]
443 * [13] unlock(task->pi_lock); release [P]
444 * unlock(lock->wait_lock); release [L]
445 * goto again;
446 */
447static int rt_mutex_adjust_prio_chain(struct task_struct *task,
448 enum rtmutex_chainwalk chwalk,
449 struct rt_mutex *orig_lock,
450 struct rt_mutex *next_lock,
451 struct rt_mutex_waiter *orig_waiter,
452 struct task_struct *top_task)
453{
454 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
455 struct rt_mutex_waiter *prerequeue_top_waiter;
456 int ret = 0, depth = 0;
457 struct rt_mutex *lock;
458 bool detect_deadlock;
459 bool requeue = true;
460
461 detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
462
463 /*
464 * The (de)boosting is a step by step approach with a lot of
465 * pitfalls. We want this to be preemptible and we want hold a
466 * maximum of two locks per step. So we have to check
467 * carefully whether things change under us.
468 */
469 again:
470 /*
471 * We limit the lock chain length for each invocation.
472 */
473 if (++depth > max_lock_depth) {
474 static int prev_max;
475
476 /*
477 * Print this only once. If the admin changes the limit,
478 * print a new message when reaching the limit again.
479 */
480 if (prev_max != max_lock_depth) {
481 prev_max = max_lock_depth;
482 printk(KERN_WARNING "Maximum lock depth %d reached "
483 "task: %s (%d)\n", max_lock_depth,
484 top_task->comm, task_pid_nr(top_task));
485 }
486 put_task_struct(task);
487
488 return -EDEADLK;
489 }
490
491 /*
492 * We are fully preemptible here and only hold the refcount on
493 * @task. So everything can have changed under us since the
494 * caller or our own code below (goto retry/again) dropped all
495 * locks.
496 */
497 retry:
498 /*
499 * [1] Task cannot go away as we did a get_task() before !
500 */
501 raw_spin_lock_irq(&task->pi_lock);
502
503 /*
504 * [2] Get the waiter on which @task is blocked on.
505 */
506 waiter = task->pi_blocked_on;
507
508 /*
509 * [3] check_exit_conditions_1() protected by task->pi_lock.
510 */
511
512 /*
513 * Check whether the end of the boosting chain has been
514 * reached or the state of the chain has changed while we
515 * dropped the locks.
516 */
517 if (!waiter)
518 goto out_unlock_pi;
519
520 /*
521 * Check the orig_waiter state. After we dropped the locks,
522 * the previous owner of the lock might have released the lock.
523 */
524 if (orig_waiter && !rt_mutex_owner(orig_lock))
525 goto out_unlock_pi;
526
527 /*
528 * We dropped all locks after taking a refcount on @task, so
529 * the task might have moved on in the lock chain or even left
530 * the chain completely and blocks now on an unrelated lock or
531 * on @orig_lock.
532 *
533 * We stored the lock on which @task was blocked in @next_lock,
534 * so we can detect the chain change.
535 */
536 if (next_lock != waiter->lock)
537 goto out_unlock_pi;
538
539 /*
540 * Drop out, when the task has no waiters. Note,
541 * top_waiter can be NULL, when we are in the deboosting
542 * mode!
543 */
544 if (top_waiter) {
545 if (!task_has_pi_waiters(task))
546 goto out_unlock_pi;
547 /*
548 * If deadlock detection is off, we stop here if we
549 * are not the top pi waiter of the task. If deadlock
550 * detection is enabled we continue, but stop the
551 * requeueing in the chain walk.
552 */
553 if (top_waiter != task_top_pi_waiter(task)) {
554 if (!detect_deadlock)
555 goto out_unlock_pi;
556 else
557 requeue = false;
558 }
559 }
560
561 /*
562 * If the waiter priority is the same as the task priority
563 * then there is no further priority adjustment necessary. If
564 * deadlock detection is off, we stop the chain walk. If its
565 * enabled we continue, but stop the requeueing in the chain
566 * walk.
567 */
568 if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
569 if (!detect_deadlock)
570 goto out_unlock_pi;
571 else
572 requeue = false;
573 }
574
575 /*
576 * [4] Get the next lock
577 */
578 lock = waiter->lock;
579 /*
580 * [5] We need to trylock here as we are holding task->pi_lock,
581 * which is the reverse lock order versus the other rtmutex
582 * operations.
583 */
584 if (!raw_spin_trylock(&lock->wait_lock)) {
585 raw_spin_unlock_irq(&task->pi_lock);
586 cpu_relax();
587 goto retry;
588 }
589
590 /*
591 * [6] check_exit_conditions_2() protected by task->pi_lock and
592 * lock->wait_lock.
593 *
594 * Deadlock detection. If the lock is the same as the original
595 * lock which caused us to walk the lock chain or if the
596 * current lock is owned by the task which initiated the chain
597 * walk, we detected a deadlock.
598 */
599 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
600 debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
601 raw_spin_unlock(&lock->wait_lock);
602 ret = -EDEADLK;
603 goto out_unlock_pi;
604 }
605
606 /*
607 * If we just follow the lock chain for deadlock detection, no
608 * need to do all the requeue operations. To avoid a truckload
609 * of conditionals around the various places below, just do the
610 * minimum chain walk checks.
611 */
612 if (!requeue) {
613 /*
614 * No requeue[7] here. Just release @task [8]
615 */
616 raw_spin_unlock(&task->pi_lock);
617 put_task_struct(task);
618
619 /*
620 * [9] check_exit_conditions_3 protected by lock->wait_lock.
621 * If there is no owner of the lock, end of chain.
622 */
623 if (!rt_mutex_owner(lock)) {
624 raw_spin_unlock_irq(&lock->wait_lock);
625 return 0;
626 }
627
628 /* [10] Grab the next task, i.e. owner of @lock */
629 task = get_task_struct(rt_mutex_owner(lock));
630 raw_spin_lock(&task->pi_lock);
631
632 /*
633 * No requeue [11] here. We just do deadlock detection.
634 *
635 * [12] Store whether owner is blocked
636 * itself. Decision is made after dropping the locks
637 */
638 next_lock = task_blocked_on_lock(task);
639 /*
640 * Get the top waiter for the next iteration
641 */
642 top_waiter = rt_mutex_top_waiter(lock);
643
644 /* [13] Drop locks */
645 raw_spin_unlock(&task->pi_lock);
646 raw_spin_unlock_irq(&lock->wait_lock);
647
648 /* If owner is not blocked, end of chain. */
649 if (!next_lock)
650 goto out_put_task;
651 goto again;
652 }
653
654 /*
655 * Store the current top waiter before doing the requeue
656 * operation on @lock. We need it for the boost/deboost
657 * decision below.
658 */
659 prerequeue_top_waiter = rt_mutex_top_waiter(lock);
660
661 /* [7] Requeue the waiter in the lock waiter tree. */
662 rt_mutex_dequeue(lock, waiter);
663
664 /*
665 * Update the waiter prio fields now that we're dequeued.
666 *
667 * These values can have changed through either:
668 *
669 * sys_sched_set_scheduler() / sys_sched_setattr()
670 *
671 * or
672 *
673 * DL CBS enforcement advancing the effective deadline.
674 *
675 * Even though pi_waiters also uses these fields, and that tree is only
676 * updated in [11], we can do this here, since we hold [L], which
677 * serializes all pi_waiters access and rb_erase() does not care about
678 * the values of the node being removed.
679 */
680 waiter->prio = task->prio;
681 waiter->deadline = task->dl.deadline;
682
683 rt_mutex_enqueue(lock, waiter);
684
685 /* [8] Release the task */
686 raw_spin_unlock(&task->pi_lock);
687 put_task_struct(task);
688
689 /*
690 * [9] check_exit_conditions_3 protected by lock->wait_lock.
691 *
692 * We must abort the chain walk if there is no lock owner even
693 * in the dead lock detection case, as we have nothing to
694 * follow here. This is the end of the chain we are walking.
695 */
696 if (!rt_mutex_owner(lock)) {
697 /*
698 * If the requeue [7] above changed the top waiter,
699 * then we need to wake the new top waiter up to try
700 * to get the lock.
701 */
702 if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
703 wake_up_process(rt_mutex_top_waiter(lock)->task);
704 raw_spin_unlock_irq(&lock->wait_lock);
705 return 0;
706 }
707
708 /* [10] Grab the next task, i.e. the owner of @lock */
709 task = get_task_struct(rt_mutex_owner(lock));
710 raw_spin_lock(&task->pi_lock);
711
712 /* [11] requeue the pi waiters if necessary */
713 if (waiter == rt_mutex_top_waiter(lock)) {
714 /*
715 * The waiter became the new top (highest priority)
716 * waiter on the lock. Replace the previous top waiter
717 * in the owner tasks pi waiters tree with this waiter
718 * and adjust the priority of the owner.
719 */
720 rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
721 rt_mutex_enqueue_pi(task, waiter);
722 rt_mutex_adjust_prio(task);
723
724 } else if (prerequeue_top_waiter == waiter) {
725 /*
726 * The waiter was the top waiter on the lock, but is
727 * no longer the top prority waiter. Replace waiter in
728 * the owner tasks pi waiters tree with the new top
729 * (highest priority) waiter and adjust the priority
730 * of the owner.
731 * The new top waiter is stored in @waiter so that
732 * @waiter == @top_waiter evaluates to true below and
733 * we continue to deboost the rest of the chain.
734 */
735 rt_mutex_dequeue_pi(task, waiter);
736 waiter = rt_mutex_top_waiter(lock);
737 rt_mutex_enqueue_pi(task, waiter);
738 rt_mutex_adjust_prio(task);
739 } else {
740 /*
741 * Nothing changed. No need to do any priority
742 * adjustment.
743 */
744 }
745
746 /*
747 * [12] check_exit_conditions_4() protected by task->pi_lock
748 * and lock->wait_lock. The actual decisions are made after we
749 * dropped the locks.
750 *
751 * Check whether the task which owns the current lock is pi
752 * blocked itself. If yes we store a pointer to the lock for
753 * the lock chain change detection above. After we dropped
754 * task->pi_lock next_lock cannot be dereferenced anymore.
755 */
756 next_lock = task_blocked_on_lock(task);
757 /*
758 * Store the top waiter of @lock for the end of chain walk
759 * decision below.
760 */
761 top_waiter = rt_mutex_top_waiter(lock);
762
763 /* [13] Drop the locks */
764 raw_spin_unlock(&task->pi_lock);
765 raw_spin_unlock_irq(&lock->wait_lock);
766
767 /*
768 * Make the actual exit decisions [12], based on the stored
769 * values.
770 *
771 * We reached the end of the lock chain. Stop right here. No
772 * point to go back just to figure that out.
773 */
774 if (!next_lock)
775 goto out_put_task;
776
777 /*
778 * If the current waiter is not the top waiter on the lock,
779 * then we can stop the chain walk here if we are not in full
780 * deadlock detection mode.
781 */
782 if (!detect_deadlock && waiter != top_waiter)
783 goto out_put_task;
784
785 goto again;
786
787 out_unlock_pi:
788 raw_spin_unlock_irq(&task->pi_lock);
789 out_put_task:
790 put_task_struct(task);
791
792 return ret;
793}
794
795/*
796 * Try to take an rt-mutex
797 *
798 * Must be called with lock->wait_lock held and interrupts disabled
799 *
800 * @lock: The lock to be acquired.
801 * @task: The task which wants to acquire the lock
802 * @waiter: The waiter that is queued to the lock's wait tree if the
803 * callsite called task_blocked_on_lock(), otherwise NULL
804 */
805static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
806 struct rt_mutex_waiter *waiter)
807{
808 lockdep_assert_held(&lock->wait_lock);
809
810 /*
811 * Before testing whether we can acquire @lock, we set the
812 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
813 * other tasks which try to modify @lock into the slow path
814 * and they serialize on @lock->wait_lock.
815 *
816 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
817 * as explained at the top of this file if and only if:
818 *
819 * - There is a lock owner. The caller must fixup the
820 * transient state if it does a trylock or leaves the lock
821 * function due to a signal or timeout.
822 *
823 * - @task acquires the lock and there are no other
824 * waiters. This is undone in rt_mutex_set_owner(@task) at
825 * the end of this function.
826 */
827 mark_rt_mutex_waiters(lock);
828
829 /*
830 * If @lock has an owner, give up.
831 */
832 if (rt_mutex_owner(lock))
833 return 0;
834
835 /*
836 * If @waiter != NULL, @task has already enqueued the waiter
837 * into @lock waiter tree. If @waiter == NULL then this is a
838 * trylock attempt.
839 */
840 if (waiter) {
841 /*
842 * If waiter is not the highest priority waiter of
843 * @lock, give up.
844 */
845 if (waiter != rt_mutex_top_waiter(lock))
846 return 0;
847
848 /*
849 * We can acquire the lock. Remove the waiter from the
850 * lock waiters tree.
851 */
852 rt_mutex_dequeue(lock, waiter);
853
854 } else {
855 /*
856 * If the lock has waiters already we check whether @task is
857 * eligible to take over the lock.
858 *
859 * If there are no other waiters, @task can acquire
860 * the lock. @task->pi_blocked_on is NULL, so it does
861 * not need to be dequeued.
862 */
863 if (rt_mutex_has_waiters(lock)) {
864 /*
865 * If @task->prio is greater than or equal to
866 * the top waiter priority (kernel view),
867 * @task lost.
868 */
869 if (!rt_mutex_waiter_less(task_to_waiter(task),
870 rt_mutex_top_waiter(lock)))
871 return 0;
872
873 /*
874 * The current top waiter stays enqueued. We
875 * don't have to change anything in the lock
876 * waiters order.
877 */
878 } else {
879 /*
880 * No waiters. Take the lock without the
881 * pi_lock dance.@task->pi_blocked_on is NULL
882 * and we have no waiters to enqueue in @task
883 * pi waiters tree.
884 */
885 goto takeit;
886 }
887 }
888
889 /*
890 * Clear @task->pi_blocked_on. Requires protection by
891 * @task->pi_lock. Redundant operation for the @waiter == NULL
892 * case, but conditionals are more expensive than a redundant
893 * store.
894 */
895 raw_spin_lock(&task->pi_lock);
896 task->pi_blocked_on = NULL;
897 /*
898 * Finish the lock acquisition. @task is the new owner. If
899 * other waiters exist we have to insert the highest priority
900 * waiter into @task->pi_waiters tree.
901 */
902 if (rt_mutex_has_waiters(lock))
903 rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
904 raw_spin_unlock(&task->pi_lock);
905
906takeit:
907 /* We got the lock. */
908 debug_rt_mutex_lock(lock);
909
910 /*
911 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
912 * are still waiters or clears it.
913 */
914 rt_mutex_set_owner(lock, task);
915
916 return 1;
917}
918
919/*
920 * Task blocks on lock.
921 *
922 * Prepare waiter and propagate pi chain
923 *
924 * This must be called with lock->wait_lock held and interrupts disabled
925 */
926static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
927 struct rt_mutex_waiter *waiter,
928 struct task_struct *task,
929 enum rtmutex_chainwalk chwalk)
930{
931 struct task_struct *owner = rt_mutex_owner(lock);
932 struct rt_mutex_waiter *top_waiter = waiter;
933 struct rt_mutex *next_lock;
934 int chain_walk = 0, res;
935
936 lockdep_assert_held(&lock->wait_lock);
937
938 /*
939 * Early deadlock detection. We really don't want the task to
940 * enqueue on itself just to untangle the mess later. It's not
941 * only an optimization. We drop the locks, so another waiter
942 * can come in before the chain walk detects the deadlock. So
943 * the other will detect the deadlock and return -EDEADLOCK,
944 * which is wrong, as the other waiter is not in a deadlock
945 * situation.
946 */
947 if (owner == task)
948 return -EDEADLK;
949
950 raw_spin_lock(&task->pi_lock);
951 waiter->task = task;
952 waiter->lock = lock;
953 waiter->prio = task->prio;
954 waiter->deadline = task->dl.deadline;
955
956 /* Get the top priority waiter on the lock */
957 if (rt_mutex_has_waiters(lock))
958 top_waiter = rt_mutex_top_waiter(lock);
959 rt_mutex_enqueue(lock, waiter);
960
961 task->pi_blocked_on = waiter;
962
963 raw_spin_unlock(&task->pi_lock);
964
965 if (!owner)
966 return 0;
967
968 raw_spin_lock(&owner->pi_lock);
969 if (waiter == rt_mutex_top_waiter(lock)) {
970 rt_mutex_dequeue_pi(owner, top_waiter);
971 rt_mutex_enqueue_pi(owner, waiter);
972
973 rt_mutex_adjust_prio(owner);
974 if (owner->pi_blocked_on)
975 chain_walk = 1;
976 } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
977 chain_walk = 1;
978 }
979
980 /* Store the lock on which owner is blocked or NULL */
981 next_lock = task_blocked_on_lock(owner);
982
983 raw_spin_unlock(&owner->pi_lock);
984 /*
985 * Even if full deadlock detection is on, if the owner is not
986 * blocked itself, we can avoid finding this out in the chain
987 * walk.
988 */
989 if (!chain_walk || !next_lock)
990 return 0;
991
992 /*
993 * The owner can't disappear while holding a lock,
994 * so the owner struct is protected by wait_lock.
995 * Gets dropped in rt_mutex_adjust_prio_chain()!
996 */
997 get_task_struct(owner);
998
999 raw_spin_unlock_irq(&lock->wait_lock);
1000
1001 res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1002 next_lock, waiter, task);
1003
1004 raw_spin_lock_irq(&lock->wait_lock);
1005
1006 return res;
1007}
1008
1009/*
1010 * Remove the top waiter from the current tasks pi waiter tree and
1011 * queue it up.
1012 *
1013 * Called with lock->wait_lock held and interrupts disabled.
1014 */
1015static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
1016 struct rt_mutex *lock)
1017{
1018 struct rt_mutex_waiter *waiter;
1019
1020 raw_spin_lock(¤t->pi_lock);
1021
1022 waiter = rt_mutex_top_waiter(lock);
1023
1024 /*
1025 * Remove it from current->pi_waiters and deboost.
1026 *
1027 * We must in fact deboost here in order to ensure we call
1028 * rt_mutex_setprio() to update p->pi_top_task before the
1029 * task unblocks.
1030 */
1031 rt_mutex_dequeue_pi(current, waiter);
1032 rt_mutex_adjust_prio(current);
1033
1034 /*
1035 * As we are waking up the top waiter, and the waiter stays
1036 * queued on the lock until it gets the lock, this lock
1037 * obviously has waiters. Just set the bit here and this has
1038 * the added benefit of forcing all new tasks into the
1039 * slow path making sure no task of lower priority than
1040 * the top waiter can steal this lock.
1041 */
1042 lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1043
1044 /*
1045 * We deboosted before waking the top waiter task such that we don't
1046 * run two tasks with the 'same' priority (and ensure the
1047 * p->pi_top_task pointer points to a blocked task). This however can
1048 * lead to priority inversion if we would get preempted after the
1049 * deboost but before waking our donor task, hence the preempt_disable()
1050 * before unlock.
1051 *
1052 * Pairs with preempt_enable() in rt_mutex_postunlock();
1053 */
1054 preempt_disable();
1055 wake_q_add(wake_q, waiter->task);
1056 raw_spin_unlock(¤t->pi_lock);
1057}
1058
1059/*
1060 * Remove a waiter from a lock and give up
1061 *
1062 * Must be called with lock->wait_lock held and interrupts disabled. I must
1063 * have just failed to try_to_take_rt_mutex().
1064 */
1065static void remove_waiter(struct rt_mutex *lock,
1066 struct rt_mutex_waiter *waiter)
1067{
1068 bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1069 struct task_struct *owner = rt_mutex_owner(lock);
1070 struct rt_mutex *next_lock;
1071
1072 lockdep_assert_held(&lock->wait_lock);
1073
1074 raw_spin_lock(¤t->pi_lock);
1075 rt_mutex_dequeue(lock, waiter);
1076 current->pi_blocked_on = NULL;
1077 raw_spin_unlock(¤t->pi_lock);
1078
1079 /*
1080 * Only update priority if the waiter was the highest priority
1081 * waiter of the lock and there is an owner to update.
1082 */
1083 if (!owner || !is_top_waiter)
1084 return;
1085
1086 raw_spin_lock(&owner->pi_lock);
1087
1088 rt_mutex_dequeue_pi(owner, waiter);
1089
1090 if (rt_mutex_has_waiters(lock))
1091 rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1092
1093 rt_mutex_adjust_prio(owner);
1094
1095 /* Store the lock on which owner is blocked or NULL */
1096 next_lock = task_blocked_on_lock(owner);
1097
1098 raw_spin_unlock(&owner->pi_lock);
1099
1100 /*
1101 * Don't walk the chain, if the owner task is not blocked
1102 * itself.
1103 */
1104 if (!next_lock)
1105 return;
1106
1107 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1108 get_task_struct(owner);
1109
1110 raw_spin_unlock_irq(&lock->wait_lock);
1111
1112 rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1113 next_lock, NULL, current);
1114
1115 raw_spin_lock_irq(&lock->wait_lock);
1116}
1117
1118/*
1119 * Recheck the pi chain, in case we got a priority setting
1120 *
1121 * Called from sched_setscheduler
1122 */
1123void rt_mutex_adjust_pi(struct task_struct *task)
1124{
1125 struct rt_mutex_waiter *waiter;
1126 struct rt_mutex *next_lock;
1127 unsigned long flags;
1128
1129 raw_spin_lock_irqsave(&task->pi_lock, flags);
1130
1131 waiter = task->pi_blocked_on;
1132 if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
1133 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1134 return;
1135 }
1136 next_lock = waiter->lock;
1137 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1138
1139 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1140 get_task_struct(task);
1141
1142 rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1143 next_lock, NULL, task);
1144}
1145
1146void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
1147{
1148 debug_rt_mutex_init_waiter(waiter);
1149 RB_CLEAR_NODE(&waiter->pi_tree_entry);
1150 RB_CLEAR_NODE(&waiter->tree_entry);
1151 waiter->task = NULL;
1152}
1153
1154/**
1155 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
1156 * @lock: the rt_mutex to take
1157 * @state: the state the task should block in (TASK_INTERRUPTIBLE
1158 * or TASK_UNINTERRUPTIBLE)
1159 * @timeout: the pre-initialized and started timer, or NULL for none
1160 * @waiter: the pre-initialized rt_mutex_waiter
1161 *
1162 * Must be called with lock->wait_lock held and interrupts disabled
1163 */
1164static int __sched
1165__rt_mutex_slowlock(struct rt_mutex *lock, int state,
1166 struct hrtimer_sleeper *timeout,
1167 struct rt_mutex_waiter *waiter)
1168{
1169 int ret = 0;
1170
1171 for (;;) {
1172 /* Try to acquire the lock: */
1173 if (try_to_take_rt_mutex(lock, current, waiter))
1174 break;
1175
1176 /*
1177 * TASK_INTERRUPTIBLE checks for signals and
1178 * timeout. Ignored otherwise.
1179 */
1180 if (likely(state == TASK_INTERRUPTIBLE)) {
1181 /* Signal pending? */
1182 if (signal_pending(current))
1183 ret = -EINTR;
1184 if (timeout && !timeout->task)
1185 ret = -ETIMEDOUT;
1186 if (ret)
1187 break;
1188 }
1189
1190 raw_spin_unlock_irq(&lock->wait_lock);
1191
1192 debug_rt_mutex_print_deadlock(waiter);
1193
1194 schedule();
1195
1196 raw_spin_lock_irq(&lock->wait_lock);
1197 set_current_state(state);
1198 }
1199
1200 __set_current_state(TASK_RUNNING);
1201 return ret;
1202}
1203
1204static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
1205 struct rt_mutex_waiter *w)
1206{
1207 /*
1208 * If the result is not -EDEADLOCK or the caller requested
1209 * deadlock detection, nothing to do here.
1210 */
1211 if (res != -EDEADLOCK || detect_deadlock)
1212 return;
1213
1214 /*
1215 * Yell lowdly and stop the task right here.
1216 */
1217 rt_mutex_print_deadlock(w);
1218 while (1) {
1219 set_current_state(TASK_INTERRUPTIBLE);
1220 schedule();
1221 }
1222}
1223
1224/*
1225 * Slow path lock function:
1226 */
1227static int __sched
1228rt_mutex_slowlock(struct rt_mutex *lock, int state,
1229 struct hrtimer_sleeper *timeout,
1230 enum rtmutex_chainwalk chwalk)
1231{
1232 struct rt_mutex_waiter waiter;
1233 unsigned long flags;
1234 int ret = 0;
1235
1236 rt_mutex_init_waiter(&waiter);
1237
1238 /*
1239 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1240 * be called in early boot if the cmpxchg() fast path is disabled
1241 * (debug, no architecture support). In this case we will acquire the
1242 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1243 * enable interrupts in that early boot case. So we need to use the
1244 * irqsave/restore variants.
1245 */
1246 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1247
1248 /* Try to acquire the lock again: */
1249 if (try_to_take_rt_mutex(lock, current, NULL)) {
1250 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1251 return 0;
1252 }
1253
1254 set_current_state(state);
1255
1256 /* Setup the timer, when timeout != NULL */
1257 if (unlikely(timeout))
1258 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1259
1260 ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1261
1262 if (likely(!ret))
1263 /* sleep on the mutex */
1264 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1265
1266 if (unlikely(ret)) {
1267 __set_current_state(TASK_RUNNING);
1268 remove_waiter(lock, &waiter);
1269 rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1270 }
1271
1272 /*
1273 * try_to_take_rt_mutex() sets the waiter bit
1274 * unconditionally. We might have to fix that up.
1275 */
1276 fixup_rt_mutex_waiters(lock);
1277
1278 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1279
1280 /* Remove pending timer: */
1281 if (unlikely(timeout))
1282 hrtimer_cancel(&timeout->timer);
1283
1284 debug_rt_mutex_free_waiter(&waiter);
1285
1286 return ret;
1287}
1288
1289static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
1290{
1291 int ret = try_to_take_rt_mutex(lock, current, NULL);
1292
1293 /*
1294 * try_to_take_rt_mutex() sets the lock waiters bit
1295 * unconditionally. Clean this up.
1296 */
1297 fixup_rt_mutex_waiters(lock);
1298
1299 return ret;
1300}
1301
1302/*
1303 * Slow path try-lock function:
1304 */
1305static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1306{
1307 unsigned long flags;
1308 int ret;
1309
1310 /*
1311 * If the lock already has an owner we fail to get the lock.
1312 * This can be done without taking the @lock->wait_lock as
1313 * it is only being read, and this is a trylock anyway.
1314 */
1315 if (rt_mutex_owner(lock))
1316 return 0;
1317
1318 /*
1319 * The mutex has currently no owner. Lock the wait lock and try to
1320 * acquire the lock. We use irqsave here to support early boot calls.
1321 */
1322 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1323
1324 ret = __rt_mutex_slowtrylock(lock);
1325
1326 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1327
1328 return ret;
1329}
1330
1331/*
1332 * Slow path to release a rt-mutex.
1333 *
1334 * Return whether the current task needs to call rt_mutex_postunlock().
1335 */
1336static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1337 struct wake_q_head *wake_q)
1338{
1339 unsigned long flags;
1340
1341 /* irqsave required to support early boot calls */
1342 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1343
1344 debug_rt_mutex_unlock(lock);
1345
1346 /*
1347 * We must be careful here if the fast path is enabled. If we
1348 * have no waiters queued we cannot set owner to NULL here
1349 * because of:
1350 *
1351 * foo->lock->owner = NULL;
1352 * rtmutex_lock(foo->lock); <- fast path
1353 * free = atomic_dec_and_test(foo->refcnt);
1354 * rtmutex_unlock(foo->lock); <- fast path
1355 * if (free)
1356 * kfree(foo);
1357 * raw_spin_unlock(foo->lock->wait_lock);
1358 *
1359 * So for the fastpath enabled kernel:
1360 *
1361 * Nothing can set the waiters bit as long as we hold
1362 * lock->wait_lock. So we do the following sequence:
1363 *
1364 * owner = rt_mutex_owner(lock);
1365 * clear_rt_mutex_waiters(lock);
1366 * raw_spin_unlock(&lock->wait_lock);
1367 * if (cmpxchg(&lock->owner, owner, 0) == owner)
1368 * return;
1369 * goto retry;
1370 *
1371 * The fastpath disabled variant is simple as all access to
1372 * lock->owner is serialized by lock->wait_lock:
1373 *
1374 * lock->owner = NULL;
1375 * raw_spin_unlock(&lock->wait_lock);
1376 */
1377 while (!rt_mutex_has_waiters(lock)) {
1378 /* Drops lock->wait_lock ! */
1379 if (unlock_rt_mutex_safe(lock, flags) == true)
1380 return false;
1381 /* Relock the rtmutex and try again */
1382 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1383 }
1384
1385 /*
1386 * The wakeup next waiter path does not suffer from the above
1387 * race. See the comments there.
1388 *
1389 * Queue the next waiter for wakeup once we release the wait_lock.
1390 */
1391 mark_wakeup_next_waiter(wake_q, lock);
1392 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1393
1394 return true; /* call rt_mutex_postunlock() */
1395}
1396
1397/*
1398 * debug aware fast / slowpath lock,trylock,unlock
1399 *
1400 * The atomic acquire/release ops are compiled away, when either the
1401 * architecture does not support cmpxchg or when debugging is enabled.
1402 */
1403static inline int
1404rt_mutex_fastlock(struct rt_mutex *lock, int state,
1405 int (*slowfn)(struct rt_mutex *lock, int state,
1406 struct hrtimer_sleeper *timeout,
1407 enum rtmutex_chainwalk chwalk))
1408{
1409 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1410 return 0;
1411
1412 return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1413}
1414
1415static inline int
1416rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1417 struct hrtimer_sleeper *timeout,
1418 enum rtmutex_chainwalk chwalk,
1419 int (*slowfn)(struct rt_mutex *lock, int state,
1420 struct hrtimer_sleeper *timeout,
1421 enum rtmutex_chainwalk chwalk))
1422{
1423 if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1424 likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1425 return 0;
1426
1427 return slowfn(lock, state, timeout, chwalk);
1428}
1429
1430static inline int
1431rt_mutex_fasttrylock(struct rt_mutex *lock,
1432 int (*slowfn)(struct rt_mutex *lock))
1433{
1434 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1435 return 1;
1436
1437 return slowfn(lock);
1438}
1439
1440/*
1441 * Performs the wakeup of the the top-waiter and re-enables preemption.
1442 */
1443void rt_mutex_postunlock(struct wake_q_head *wake_q)
1444{
1445 wake_up_q(wake_q);
1446
1447 /* Pairs with preempt_disable() in rt_mutex_slowunlock() */
1448 preempt_enable();
1449}
1450
1451static inline void
1452rt_mutex_fastunlock(struct rt_mutex *lock,
1453 bool (*slowfn)(struct rt_mutex *lock,
1454 struct wake_q_head *wqh))
1455{
1456 DEFINE_WAKE_Q(wake_q);
1457
1458 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1459 return;
1460
1461 if (slowfn(lock, &wake_q))
1462 rt_mutex_postunlock(&wake_q);
1463}
1464
1465static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
1466{
1467 might_sleep();
1468
1469 mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
1470 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1471}
1472
1473#ifdef CONFIG_DEBUG_LOCK_ALLOC
1474/**
1475 * rt_mutex_lock_nested - lock a rt_mutex
1476 *
1477 * @lock: the rt_mutex to be locked
1478 * @subclass: the lockdep subclass
1479 */
1480void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
1481{
1482 __rt_mutex_lock(lock, subclass);
1483}
1484EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
1485
1486#else /* !CONFIG_DEBUG_LOCK_ALLOC */
1487
1488/**
1489 * rt_mutex_lock - lock a rt_mutex
1490 *
1491 * @lock: the rt_mutex to be locked
1492 */
1493void __sched rt_mutex_lock(struct rt_mutex *lock)
1494{
1495 __rt_mutex_lock(lock, 0);
1496}
1497EXPORT_SYMBOL_GPL(rt_mutex_lock);
1498#endif
1499
1500/**
1501 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1502 *
1503 * @lock: the rt_mutex to be locked
1504 *
1505 * Returns:
1506 * 0 on success
1507 * -EINTR when interrupted by a signal
1508 */
1509int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1510{
1511 int ret;
1512
1513 might_sleep();
1514
1515 mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1516 ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1517 if (ret)
1518 mutex_release(&lock->dep_map, _RET_IP_);
1519
1520 return ret;
1521}
1522EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1523
1524/*
1525 * Futex variant, must not use fastpath.
1526 */
1527int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
1528{
1529 return rt_mutex_slowtrylock(lock);
1530}
1531
1532int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
1533{
1534 return __rt_mutex_slowtrylock(lock);
1535}
1536
1537/**
1538 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1539 * the timeout structure is provided
1540 * by the caller
1541 *
1542 * @lock: the rt_mutex to be locked
1543 * @timeout: timeout structure or NULL (no timeout)
1544 *
1545 * Returns:
1546 * 0 on success
1547 * -EINTR when interrupted by a signal
1548 * -ETIMEDOUT when the timeout expired
1549 */
1550int
1551rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1552{
1553 int ret;
1554
1555 might_sleep();
1556
1557 mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1558 ret = rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1559 RT_MUTEX_MIN_CHAINWALK,
1560 rt_mutex_slowlock);
1561 if (ret)
1562 mutex_release(&lock->dep_map, _RET_IP_);
1563
1564 return ret;
1565}
1566EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1567
1568/**
1569 * rt_mutex_trylock - try to lock a rt_mutex
1570 *
1571 * @lock: the rt_mutex to be locked
1572 *
1573 * This function can only be called in thread context. It's safe to
1574 * call it from atomic regions, but not from hard interrupt or soft
1575 * interrupt context.
1576 *
1577 * Returns 1 on success and 0 on contention
1578 */
1579int __sched rt_mutex_trylock(struct rt_mutex *lock)
1580{
1581 int ret;
1582
1583 if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
1584 return 0;
1585
1586 ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1587 if (ret)
1588 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1589
1590 return ret;
1591}
1592EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1593
1594/**
1595 * rt_mutex_unlock - unlock a rt_mutex
1596 *
1597 * @lock: the rt_mutex to be unlocked
1598 */
1599void __sched rt_mutex_unlock(struct rt_mutex *lock)
1600{
1601 mutex_release(&lock->dep_map, _RET_IP_);
1602 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1603}
1604EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1605
1606/**
1607 * Futex variant, that since futex variants do not use the fast-path, can be
1608 * simple and will not need to retry.
1609 */
1610bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
1611 struct wake_q_head *wake_q)
1612{
1613 lockdep_assert_held(&lock->wait_lock);
1614
1615 debug_rt_mutex_unlock(lock);
1616
1617 if (!rt_mutex_has_waiters(lock)) {
1618 lock->owner = NULL;
1619 return false; /* done */
1620 }
1621
1622 /*
1623 * We've already deboosted, mark_wakeup_next_waiter() will
1624 * retain preempt_disabled when we drop the wait_lock, to
1625 * avoid inversion prior to the wakeup. preempt_disable()
1626 * therein pairs with rt_mutex_postunlock().
1627 */
1628 mark_wakeup_next_waiter(wake_q, lock);
1629
1630 return true; /* call postunlock() */
1631}
1632
1633void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
1634{
1635 DEFINE_WAKE_Q(wake_q);
1636 unsigned long flags;
1637 bool postunlock;
1638
1639 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1640 postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
1641 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1642
1643 if (postunlock)
1644 rt_mutex_postunlock(&wake_q);
1645}
1646
1647/**
1648 * rt_mutex_destroy - mark a mutex unusable
1649 * @lock: the mutex to be destroyed
1650 *
1651 * This function marks the mutex uninitialized, and any subsequent
1652 * use of the mutex is forbidden. The mutex must not be locked when
1653 * this function is called.
1654 */
1655void rt_mutex_destroy(struct rt_mutex *lock)
1656{
1657 WARN_ON(rt_mutex_is_locked(lock));
1658#ifdef CONFIG_DEBUG_RT_MUTEXES
1659 lock->magic = NULL;
1660#endif
1661}
1662EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1663
1664/**
1665 * __rt_mutex_init - initialize the rt lock
1666 *
1667 * @lock: the rt lock to be initialized
1668 *
1669 * Initialize the rt lock to unlocked state.
1670 *
1671 * Initializing of a locked rt lock is not allowed
1672 */
1673void __rt_mutex_init(struct rt_mutex *lock, const char *name,
1674 struct lock_class_key *key)
1675{
1676 lock->owner = NULL;
1677 raw_spin_lock_init(&lock->wait_lock);
1678 lock->waiters = RB_ROOT_CACHED;
1679
1680 if (name && key)
1681 debug_rt_mutex_init(lock, name, key);
1682}
1683EXPORT_SYMBOL_GPL(__rt_mutex_init);
1684
1685/**
1686 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1687 * proxy owner
1688 *
1689 * @lock: the rt_mutex to be locked
1690 * @proxy_owner:the task to set as owner
1691 *
1692 * No locking. Caller has to do serializing itself
1693 *
1694 * Special API call for PI-futex support. This initializes the rtmutex and
1695 * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
1696 * possible at this point because the pi_state which contains the rtmutex
1697 * is not yet visible to other tasks.
1698 */
1699void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1700 struct task_struct *proxy_owner)
1701{
1702 __rt_mutex_init(lock, NULL, NULL);
1703 debug_rt_mutex_proxy_lock(lock, proxy_owner);
1704 rt_mutex_set_owner(lock, proxy_owner);
1705}
1706
1707/**
1708 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1709 *
1710 * @lock: the rt_mutex to be locked
1711 *
1712 * No locking. Caller has to do serializing itself
1713 *
1714 * Special API call for PI-futex support. This merrily cleans up the rtmutex
1715 * (debugging) state. Concurrent operations on this rt_mutex are not
1716 * possible because it belongs to the pi_state which is about to be freed
1717 * and it is not longer visible to other tasks.
1718 */
1719void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1720 struct task_struct *proxy_owner)
1721{
1722 debug_rt_mutex_proxy_unlock(lock);
1723 rt_mutex_set_owner(lock, NULL);
1724}
1725
1726/**
1727 * __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1728 * @lock: the rt_mutex to take
1729 * @waiter: the pre-initialized rt_mutex_waiter
1730 * @task: the task to prepare
1731 *
1732 * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
1733 * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
1734 *
1735 * NOTE: does _NOT_ remove the @waiter on failure; must either call
1736 * rt_mutex_wait_proxy_lock() or rt_mutex_cleanup_proxy_lock() after this.
1737 *
1738 * Returns:
1739 * 0 - task blocked on lock
1740 * 1 - acquired the lock for task, caller should wake it up
1741 * <0 - error
1742 *
1743 * Special API call for PI-futex support.
1744 */
1745int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1746 struct rt_mutex_waiter *waiter,
1747 struct task_struct *task)
1748{
1749 int ret;
1750
1751 lockdep_assert_held(&lock->wait_lock);
1752
1753 if (try_to_take_rt_mutex(lock, task, NULL))
1754 return 1;
1755
1756 /* We enforce deadlock detection for futexes */
1757 ret = task_blocks_on_rt_mutex(lock, waiter, task,
1758 RT_MUTEX_FULL_CHAINWALK);
1759
1760 if (ret && !rt_mutex_owner(lock)) {
1761 /*
1762 * Reset the return value. We might have
1763 * returned with -EDEADLK and the owner
1764 * released the lock while we were walking the
1765 * pi chain. Let the waiter sort it out.
1766 */
1767 ret = 0;
1768 }
1769
1770 debug_rt_mutex_print_deadlock(waiter);
1771
1772 return ret;
1773}
1774
1775/**
1776 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1777 * @lock: the rt_mutex to take
1778 * @waiter: the pre-initialized rt_mutex_waiter
1779 * @task: the task to prepare
1780 *
1781 * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
1782 * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
1783 *
1784 * NOTE: unlike __rt_mutex_start_proxy_lock this _DOES_ remove the @waiter
1785 * on failure.
1786 *
1787 * Returns:
1788 * 0 - task blocked on lock
1789 * 1 - acquired the lock for task, caller should wake it up
1790 * <0 - error
1791 *
1792 * Special API call for PI-futex support.
1793 */
1794int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1795 struct rt_mutex_waiter *waiter,
1796 struct task_struct *task)
1797{
1798 int ret;
1799
1800 raw_spin_lock_irq(&lock->wait_lock);
1801 ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
1802 if (unlikely(ret))
1803 remove_waiter(lock, waiter);
1804 raw_spin_unlock_irq(&lock->wait_lock);
1805
1806 return ret;
1807}
1808
1809/**
1810 * rt_mutex_next_owner - return the next owner of the lock
1811 *
1812 * @lock: the rt lock query
1813 *
1814 * Returns the next owner of the lock or NULL
1815 *
1816 * Caller has to serialize against other accessors to the lock
1817 * itself.
1818 *
1819 * Special API call for PI-futex support
1820 */
1821struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1822{
1823 if (!rt_mutex_has_waiters(lock))
1824 return NULL;
1825
1826 return rt_mutex_top_waiter(lock)->task;
1827}
1828
1829/**
1830 * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
1831 * @lock: the rt_mutex we were woken on
1832 * @to: the timeout, null if none. hrtimer should already have
1833 * been started.
1834 * @waiter: the pre-initialized rt_mutex_waiter
1835 *
1836 * Wait for the the lock acquisition started on our behalf by
1837 * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
1838 * rt_mutex_cleanup_proxy_lock().
1839 *
1840 * Returns:
1841 * 0 - success
1842 * <0 - error, one of -EINTR, -ETIMEDOUT
1843 *
1844 * Special API call for PI-futex support
1845 */
1846int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
1847 struct hrtimer_sleeper *to,
1848 struct rt_mutex_waiter *waiter)
1849{
1850 int ret;
1851
1852 raw_spin_lock_irq(&lock->wait_lock);
1853 /* sleep on the mutex */
1854 set_current_state(TASK_INTERRUPTIBLE);
1855 ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1856 /*
1857 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1858 * have to fix that up.
1859 */
1860 fixup_rt_mutex_waiters(lock);
1861 raw_spin_unlock_irq(&lock->wait_lock);
1862
1863 return ret;
1864}
1865
1866/**
1867 * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
1868 * @lock: the rt_mutex we were woken on
1869 * @waiter: the pre-initialized rt_mutex_waiter
1870 *
1871 * Attempt to clean up after a failed __rt_mutex_start_proxy_lock() or
1872 * rt_mutex_wait_proxy_lock().
1873 *
1874 * Unless we acquired the lock; we're still enqueued on the wait-list and can
1875 * in fact still be granted ownership until we're removed. Therefore we can
1876 * find we are in fact the owner and must disregard the
1877 * rt_mutex_wait_proxy_lock() failure.
1878 *
1879 * Returns:
1880 * true - did the cleanup, we done.
1881 * false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
1882 * caller should disregards its return value.
1883 *
1884 * Special API call for PI-futex support
1885 */
1886bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
1887 struct rt_mutex_waiter *waiter)
1888{
1889 bool cleanup = false;
1890
1891 raw_spin_lock_irq(&lock->wait_lock);
1892 /*
1893 * Do an unconditional try-lock, this deals with the lock stealing
1894 * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
1895 * sets a NULL owner.
1896 *
1897 * We're not interested in the return value, because the subsequent
1898 * test on rt_mutex_owner() will infer that. If the trylock succeeded,
1899 * we will own the lock and it will have removed the waiter. If we
1900 * failed the trylock, we're still not owner and we need to remove
1901 * ourselves.
1902 */
1903 try_to_take_rt_mutex(lock, current, waiter);
1904 /*
1905 * Unless we're the owner; we're still enqueued on the wait_list.
1906 * So check if we became owner, if not, take us off the wait_list.
1907 */
1908 if (rt_mutex_owner(lock) != current) {
1909 remove_waiter(lock, waiter);
1910 cleanup = true;
1911 }
1912 /*
1913 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1914 * have to fix that up.
1915 */
1916 fixup_rt_mutex_waiters(lock);
1917
1918 raw_spin_unlock_irq(&lock->wait_lock);
1919
1920 return cleanup;
1921}