projects/linux·blob v3.16 · refs

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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 <[email protected]>
7 * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <[email protected]>
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
87/*
88 * Safe fastpath aware unlock:
89 * 1) Clear the waiters bit
90 * 2) Drop lock->wait_lock
91 * 3) Try to unlock the lock with cmpxchg
92 */
93static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock)
94 __releases(lock->wait_lock)
95{
96 struct task_struct *owner = rt_mutex_owner(lock);
97
98 clear_rt_mutex_waiters(lock);
99 raw_spin_unlock(&lock->wait_lock);
100 /*
101 * If a new waiter comes in between the unlock and the cmpxchg
102 * we have two situations:
103 *
104 * unlock(wait_lock);
105 * lock(wait_lock);
106 * cmpxchg(p, owner, 0) == owner
107 * mark_rt_mutex_waiters(lock);
108 * acquire(lock);
109 * or:
110 *
111 * unlock(wait_lock);
112 * lock(wait_lock);
113 * mark_rt_mutex_waiters(lock);
114 *
115 * cmpxchg(p, owner, 0) != owner
116 * enqueue_waiter();
117 * unlock(wait_lock);
118 * lock(wait_lock);
119 * wake waiter();
120 * unlock(wait_lock);
121 * lock(wait_lock);
122 * acquire(lock);
123 */
124 return rt_mutex_cmpxchg(lock, owner, NULL);
125}
126
127#else
128# define rt_mutex_cmpxchg(l,c,n) (0)
129static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
130{
131 lock->owner = (struct task_struct *)
132 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
133}
134
135/*
136 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
137 */
138static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock)
139 __releases(lock->wait_lock)
140{
141 lock->owner = NULL;
142 raw_spin_unlock(&lock->wait_lock);
143 return true;
144}
145#endif
146
147static inline int
148rt_mutex_waiter_less(struct rt_mutex_waiter *left,
149 struct rt_mutex_waiter *right)
150{
151 if (left->prio < right->prio)
152 return 1;
153
154 /*
155 * If both waiters have dl_prio(), we check the deadlines of the
156 * associated tasks.
157 * If left waiter has a dl_prio(), and we didn't return 1 above,
158 * then right waiter has a dl_prio() too.
159 */
160 if (dl_prio(left->prio))
161 return (left->task->dl.deadline < right->task->dl.deadline);
162
163 return 0;
164}
165
166static void
167rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
168{
169 struct rb_node **link = &lock->waiters.rb_node;
170 struct rb_node *parent = NULL;
171 struct rt_mutex_waiter *entry;
172 int leftmost = 1;
173
174 while (*link) {
175 parent = *link;
176 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
177 if (rt_mutex_waiter_less(waiter, entry)) {
178 link = &parent->rb_left;
179 } else {
180 link = &parent->rb_right;
181 leftmost = 0;
182 }
183 }
184
185 if (leftmost)
186 lock->waiters_leftmost = &waiter->tree_entry;
187
188 rb_link_node(&waiter->tree_entry, parent, link);
189 rb_insert_color(&waiter->tree_entry, &lock->waiters);
190}
191
192static void
193rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
194{
195 if (RB_EMPTY_NODE(&waiter->tree_entry))
196 return;
197
198 if (lock->waiters_leftmost == &waiter->tree_entry)
199 lock->waiters_leftmost = rb_next(&waiter->tree_entry);
200
201 rb_erase(&waiter->tree_entry, &lock->waiters);
202 RB_CLEAR_NODE(&waiter->tree_entry);
203}
204
205static void
206rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
207{
208 struct rb_node **link = &task->pi_waiters.rb_node;
209 struct rb_node *parent = NULL;
210 struct rt_mutex_waiter *entry;
211 int leftmost = 1;
212
213 while (*link) {
214 parent = *link;
215 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
216 if (rt_mutex_waiter_less(waiter, entry)) {
217 link = &parent->rb_left;
218 } else {
219 link = &parent->rb_right;
220 leftmost = 0;
221 }
222 }
223
224 if (leftmost)
225 task->pi_waiters_leftmost = &waiter->pi_tree_entry;
226
227 rb_link_node(&waiter->pi_tree_entry, parent, link);
228 rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
229}
230
231static void
232rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
233{
234 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
235 return;
236
237 if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
238 task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
239
240 rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
241 RB_CLEAR_NODE(&waiter->pi_tree_entry);
242}
243
244/*
245 * Calculate task priority from the waiter tree priority
246 *
247 * Return task->normal_prio when the waiter tree is empty or when
248 * the waiter is not allowed to do priority boosting
249 */
250int rt_mutex_getprio(struct task_struct *task)
251{
252 if (likely(!task_has_pi_waiters(task)))
253 return task->normal_prio;
254
255 return min(task_top_pi_waiter(task)->prio,
256 task->normal_prio);
257}
258
259struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
260{
261 if (likely(!task_has_pi_waiters(task)))
262 return NULL;
263
264 return task_top_pi_waiter(task)->task;
265}
266
267/*
268 * Called by sched_setscheduler() to check whether the priority change
269 * is overruled by a possible priority boosting.
270 */
271int rt_mutex_check_prio(struct task_struct *task, int newprio)
272{
273 if (!task_has_pi_waiters(task))
274 return 0;
275
276 return task_top_pi_waiter(task)->task->prio <= newprio;
277}
278
279/*
280 * Adjust the priority of a task, after its pi_waiters got modified.
281 *
282 * This can be both boosting and unboosting. task->pi_lock must be held.
283 */
284static void __rt_mutex_adjust_prio(struct task_struct *task)
285{
286 int prio = rt_mutex_getprio(task);
287
288 if (task->prio != prio || dl_prio(prio))
289 rt_mutex_setprio(task, prio);
290}
291
292/*
293 * Adjust task priority (undo boosting). Called from the exit path of
294 * rt_mutex_slowunlock() and rt_mutex_slowlock().
295 *
296 * (Note: We do this outside of the protection of lock->wait_lock to
297 * allow the lock to be taken while or before we readjust the priority
298 * of task. We do not use the spin_xx_mutex() variants here as we are
299 * outside of the debug path.)
300 */
301static void rt_mutex_adjust_prio(struct task_struct *task)
302{
303 unsigned long flags;
304
305 raw_spin_lock_irqsave(&task->pi_lock, flags);
306 __rt_mutex_adjust_prio(task);
307 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
308}
309
310/*
311 * Max number of times we'll walk the boosting chain:
312 */
313int max_lock_depth = 1024;
314
315static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
316{
317 return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
318}
319
320/*
321 * Adjust the priority chain. Also used for deadlock detection.
322 * Decreases task's usage by one - may thus free the task.
323 *
324 * @task: the task owning the mutex (owner) for which a chain walk is
325 * probably needed
326 * @deadlock_detect: do we have to carry out deadlock detection?
327 * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
328 * things for a task that has just got its priority adjusted, and
329 * is waiting on a mutex)
330 * @next_lock: the mutex on which the owner of @orig_lock was blocked before
331 * we dropped its pi_lock. Is never dereferenced, only used for
332 * comparison to detect lock chain changes.
333 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
334 * its priority to the mutex owner (can be NULL in the case
335 * depicted above or if the top waiter is gone away and we are
336 * actually deboosting the owner)
337 * @top_task: the current top waiter
338 *
339 * Returns 0 or -EDEADLK.
340 */
341static int rt_mutex_adjust_prio_chain(struct task_struct *task,
342 int deadlock_detect,
343 struct rt_mutex *orig_lock,
344 struct rt_mutex *next_lock,
345 struct rt_mutex_waiter *orig_waiter,
346 struct task_struct *top_task)
347{
348 struct rt_mutex *lock;
349 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
350 int detect_deadlock, ret = 0, depth = 0;
351 unsigned long flags;
352
353 detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
354 deadlock_detect);
355
356 /*
357 * The (de)boosting is a step by step approach with a lot of
358 * pitfalls. We want this to be preemptible and we want hold a
359 * maximum of two locks per step. So we have to check
360 * carefully whether things change under us.
361 */
362 again:
363 if (++depth > max_lock_depth) {
364 static int prev_max;
365
366 /*
367 * Print this only once. If the admin changes the limit,
368 * print a new message when reaching the limit again.
369 */
370 if (prev_max != max_lock_depth) {
371 prev_max = max_lock_depth;
372 printk(KERN_WARNING "Maximum lock depth %d reached "
373 "task: %s (%d)\n", max_lock_depth,
374 top_task->comm, task_pid_nr(top_task));
375 }
376 put_task_struct(task);
377
378 return -EDEADLK;
379 }
380 retry:
381 /*
382 * Task can not go away as we did a get_task() before !
383 */
384 raw_spin_lock_irqsave(&task->pi_lock, flags);
385
386 waiter = task->pi_blocked_on;
387 /*
388 * Check whether the end of the boosting chain has been
389 * reached or the state of the chain has changed while we
390 * dropped the locks.
391 */
392 if (!waiter)
393 goto out_unlock_pi;
394
395 /*
396 * Check the orig_waiter state. After we dropped the locks,
397 * the previous owner of the lock might have released the lock.
398 */
399 if (orig_waiter && !rt_mutex_owner(orig_lock))
400 goto out_unlock_pi;
401
402 /*
403 * We dropped all locks after taking a refcount on @task, so
404 * the task might have moved on in the lock chain or even left
405 * the chain completely and blocks now on an unrelated lock or
406 * on @orig_lock.
407 *
408 * We stored the lock on which @task was blocked in @next_lock,
409 * so we can detect the chain change.
410 */
411 if (next_lock != waiter->lock)
412 goto out_unlock_pi;
413
414 /*
415 * Drop out, when the task has no waiters. Note,
416 * top_waiter can be NULL, when we are in the deboosting
417 * mode!
418 */
419 if (top_waiter) {
420 if (!task_has_pi_waiters(task))
421 goto out_unlock_pi;
422 /*
423 * If deadlock detection is off, we stop here if we
424 * are not the top pi waiter of the task.
425 */
426 if (!detect_deadlock && top_waiter != task_top_pi_waiter(task))
427 goto out_unlock_pi;
428 }
429
430 /*
431 * When deadlock detection is off then we check, if further
432 * priority adjustment is necessary.
433 */
434 if (!detect_deadlock && waiter->prio == task->prio)
435 goto out_unlock_pi;
436
437 lock = waiter->lock;
438 if (!raw_spin_trylock(&lock->wait_lock)) {
439 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
440 cpu_relax();
441 goto retry;
442 }
443
444 /*
445 * Deadlock detection. If the lock is the same as the original
446 * lock which caused us to walk the lock chain or if the
447 * current lock is owned by the task which initiated the chain
448 * walk, we detected a deadlock.
449 */
450 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
451 debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
452 raw_spin_unlock(&lock->wait_lock);
453 ret = -EDEADLK;
454 goto out_unlock_pi;
455 }
456
457 top_waiter = rt_mutex_top_waiter(lock);
458
459 /* Requeue the waiter */
460 rt_mutex_dequeue(lock, waiter);
461 waiter->prio = task->prio;
462 rt_mutex_enqueue(lock, waiter);
463
464 /* Release the task */
465 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
466 if (!rt_mutex_owner(lock)) {
467 /*
468 * If the requeue above changed the top waiter, then we need
469 * to wake the new top waiter up to try to get the lock.
470 */
471
472 if (top_waiter != rt_mutex_top_waiter(lock))
473 wake_up_process(rt_mutex_top_waiter(lock)->task);
474 raw_spin_unlock(&lock->wait_lock);
475 goto out_put_task;
476 }
477 put_task_struct(task);
478
479 /* Grab the next task */
480 task = rt_mutex_owner(lock);
481 get_task_struct(task);
482 raw_spin_lock_irqsave(&task->pi_lock, flags);
483
484 if (waiter == rt_mutex_top_waiter(lock)) {
485 /* Boost the owner */
486 rt_mutex_dequeue_pi(task, top_waiter);
487 rt_mutex_enqueue_pi(task, waiter);
488 __rt_mutex_adjust_prio(task);
489
490 } else if (top_waiter == waiter) {
491 /* Deboost the owner */
492 rt_mutex_dequeue_pi(task, waiter);
493 waiter = rt_mutex_top_waiter(lock);
494 rt_mutex_enqueue_pi(task, waiter);
495 __rt_mutex_adjust_prio(task);
496 }
497
498 /*
499 * Check whether the task which owns the current lock is pi
500 * blocked itself. If yes we store a pointer to the lock for
501 * the lock chain change detection above. After we dropped
502 * task->pi_lock next_lock cannot be dereferenced anymore.
503 */
504 next_lock = task_blocked_on_lock(task);
505
506 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
507
508 top_waiter = rt_mutex_top_waiter(lock);
509 raw_spin_unlock(&lock->wait_lock);
510
511 /*
512 * We reached the end of the lock chain. Stop right here. No
513 * point to go back just to figure that out.
514 */
515 if (!next_lock)
516 goto out_put_task;
517
518 if (!detect_deadlock && waiter != top_waiter)
519 goto out_put_task;
520
521 goto again;
522
523 out_unlock_pi:
524 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
525 out_put_task:
526 put_task_struct(task);
527
528 return ret;
529}
530
531/*
532 * Try to take an rt-mutex
533 *
534 * Must be called with lock->wait_lock held.
535 *
536 * @lock: the lock to be acquired.
537 * @task: the task which wants to acquire the lock
538 * @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
539 */
540static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
541 struct rt_mutex_waiter *waiter)
542{
543 /*
544 * We have to be careful here if the atomic speedups are
545 * enabled, such that, when
546 * - no other waiter is on the lock
547 * - the lock has been released since we did the cmpxchg
548 * the lock can be released or taken while we are doing the
549 * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
550 *
551 * The atomic acquire/release aware variant of
552 * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
553 * the WAITERS bit, the atomic release / acquire can not
554 * happen anymore and lock->wait_lock protects us from the
555 * non-atomic case.
556 *
557 * Note, that this might set lock->owner =
558 * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
559 * any more. This is fixed up when we take the ownership.
560 * This is the transitional state explained at the top of this file.
561 */
562 mark_rt_mutex_waiters(lock);
563
564 if (rt_mutex_owner(lock))
565 return 0;
566
567 /*
568 * It will get the lock because of one of these conditions:
569 * 1) there is no waiter
570 * 2) higher priority than waiters
571 * 3) it is top waiter
572 */
573 if (rt_mutex_has_waiters(lock)) {
574 if (task->prio >= rt_mutex_top_waiter(lock)->prio) {
575 if (!waiter || waiter != rt_mutex_top_waiter(lock))
576 return 0;
577 }
578 }
579
580 if (waiter || rt_mutex_has_waiters(lock)) {
581 unsigned long flags;
582 struct rt_mutex_waiter *top;
583
584 raw_spin_lock_irqsave(&task->pi_lock, flags);
585
586 /* remove the queued waiter. */
587 if (waiter) {
588 rt_mutex_dequeue(lock, waiter);
589 task->pi_blocked_on = NULL;
590 }
591
592 /*
593 * We have to enqueue the top waiter(if it exists) into
594 * task->pi_waiters list.
595 */
596 if (rt_mutex_has_waiters(lock)) {
597 top = rt_mutex_top_waiter(lock);
598 rt_mutex_enqueue_pi(task, top);
599 }
600 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
601 }
602
603 /* We got the lock. */
604 debug_rt_mutex_lock(lock);
605
606 rt_mutex_set_owner(lock, task);
607
608 rt_mutex_deadlock_account_lock(lock, task);
609
610 return 1;
611}
612
613/*
614 * Task blocks on lock.
615 *
616 * Prepare waiter and propagate pi chain
617 *
618 * This must be called with lock->wait_lock held.
619 */
620static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
621 struct rt_mutex_waiter *waiter,
622 struct task_struct *task,
623 int detect_deadlock)
624{
625 struct task_struct *owner = rt_mutex_owner(lock);
626 struct rt_mutex_waiter *top_waiter = waiter;
627 struct rt_mutex *next_lock;
628 int chain_walk = 0, res;
629 unsigned long flags;
630
631 /*
632 * Early deadlock detection. We really don't want the task to
633 * enqueue on itself just to untangle the mess later. It's not
634 * only an optimization. We drop the locks, so another waiter
635 * can come in before the chain walk detects the deadlock. So
636 * the other will detect the deadlock and return -EDEADLOCK,
637 * which is wrong, as the other waiter is not in a deadlock
638 * situation.
639 */
640 if (owner == task)
641 return -EDEADLK;
642
643 raw_spin_lock_irqsave(&task->pi_lock, flags);
644 __rt_mutex_adjust_prio(task);
645 waiter->task = task;
646 waiter->lock = lock;
647 waiter->prio = task->prio;
648
649 /* Get the top priority waiter on the lock */
650 if (rt_mutex_has_waiters(lock))
651 top_waiter = rt_mutex_top_waiter(lock);
652 rt_mutex_enqueue(lock, waiter);
653
654 task->pi_blocked_on = waiter;
655
656 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
657
658 if (!owner)
659 return 0;
660
661 raw_spin_lock_irqsave(&owner->pi_lock, flags);
662 if (waiter == rt_mutex_top_waiter(lock)) {
663 rt_mutex_dequeue_pi(owner, top_waiter);
664 rt_mutex_enqueue_pi(owner, waiter);
665
666 __rt_mutex_adjust_prio(owner);
667 if (owner->pi_blocked_on)
668 chain_walk = 1;
669 } else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock)) {
670 chain_walk = 1;
671 }
672
673 /* Store the lock on which owner is blocked or NULL */
674 next_lock = task_blocked_on_lock(owner);
675
676 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
677 /*
678 * Even if full deadlock detection is on, if the owner is not
679 * blocked itself, we can avoid finding this out in the chain
680 * walk.
681 */
682 if (!chain_walk || !next_lock)
683 return 0;
684
685 /*
686 * The owner can't disappear while holding a lock,
687 * so the owner struct is protected by wait_lock.
688 * Gets dropped in rt_mutex_adjust_prio_chain()!
689 */
690 get_task_struct(owner);
691
692 raw_spin_unlock(&lock->wait_lock);
693
694 res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock,
695 next_lock, waiter, task);
696
697 raw_spin_lock(&lock->wait_lock);
698
699 return res;
700}
701
702/*
703 * Wake up the next waiter on the lock.
704 *
705 * Remove the top waiter from the current tasks pi waiter list and
706 * wake it up.
707 *
708 * Called with lock->wait_lock held.
709 */
710static void wakeup_next_waiter(struct rt_mutex *lock)
711{
712 struct rt_mutex_waiter *waiter;
713 unsigned long flags;
714
715 raw_spin_lock_irqsave(&current->pi_lock, flags);
716
717 waiter = rt_mutex_top_waiter(lock);
718
719 /*
720 * Remove it from current->pi_waiters. We do not adjust a
721 * possible priority boost right now. We execute wakeup in the
722 * boosted mode and go back to normal after releasing
723 * lock->wait_lock.
724 */
725 rt_mutex_dequeue_pi(current, waiter);
726
727 /*
728 * As we are waking up the top waiter, and the waiter stays
729 * queued on the lock until it gets the lock, this lock
730 * obviously has waiters. Just set the bit here and this has
731 * the added benefit of forcing all new tasks into the
732 * slow path making sure no task of lower priority than
733 * the top waiter can steal this lock.
734 */
735 lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
736
737 raw_spin_unlock_irqrestore(&current->pi_lock, flags);
738
739 /*
740 * It's safe to dereference waiter as it cannot go away as
741 * long as we hold lock->wait_lock. The waiter task needs to
742 * acquire it in order to dequeue the waiter.
743 */
744 wake_up_process(waiter->task);
745}
746
747/*
748 * Remove a waiter from a lock and give up
749 *
750 * Must be called with lock->wait_lock held and
751 * have just failed to try_to_take_rt_mutex().
752 */
753static void remove_waiter(struct rt_mutex *lock,
754 struct rt_mutex_waiter *waiter)
755{
756 int first = (waiter == rt_mutex_top_waiter(lock));
757 struct task_struct *owner = rt_mutex_owner(lock);
758 struct rt_mutex *next_lock = NULL;
759 unsigned long flags;
760
761 raw_spin_lock_irqsave(&current->pi_lock, flags);
762 rt_mutex_dequeue(lock, waiter);
763 current->pi_blocked_on = NULL;
764 raw_spin_unlock_irqrestore(&current->pi_lock, flags);
765
766 if (!owner)
767 return;
768
769 if (first) {
770
771 raw_spin_lock_irqsave(&owner->pi_lock, flags);
772
773 rt_mutex_dequeue_pi(owner, waiter);
774
775 if (rt_mutex_has_waiters(lock)) {
776 struct rt_mutex_waiter *next;
777
778 next = rt_mutex_top_waiter(lock);
779 rt_mutex_enqueue_pi(owner, next);
780 }
781 __rt_mutex_adjust_prio(owner);
782
783 /* Store the lock on which owner is blocked or NULL */
784 next_lock = task_blocked_on_lock(owner);
785
786 raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
787 }
788
789 if (!next_lock)
790 return;
791
792 /* gets dropped in rt_mutex_adjust_prio_chain()! */
793 get_task_struct(owner);
794
795 raw_spin_unlock(&lock->wait_lock);
796
797 rt_mutex_adjust_prio_chain(owner, 0, lock, next_lock, NULL, current);
798
799 raw_spin_lock(&lock->wait_lock);
800}
801
802/*
803 * Recheck the pi chain, in case we got a priority setting
804 *
805 * Called from sched_setscheduler
806 */
807void rt_mutex_adjust_pi(struct task_struct *task)
808{
809 struct rt_mutex_waiter *waiter;
810 struct rt_mutex *next_lock;
811 unsigned long flags;
812
813 raw_spin_lock_irqsave(&task->pi_lock, flags);
814
815 waiter = task->pi_blocked_on;
816 if (!waiter || (waiter->prio == task->prio &&
817 !dl_prio(task->prio))) {
818 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
819 return;
820 }
821 next_lock = waiter->lock;
822 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
823
824 /* gets dropped in rt_mutex_adjust_prio_chain()! */
825 get_task_struct(task);
826
827 rt_mutex_adjust_prio_chain(task, 0, NULL, next_lock, NULL, task);
828}
829
830/**
831 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
832 * @lock: the rt_mutex to take
833 * @state: the state the task should block in (TASK_INTERRUPTIBLE
834 * or TASK_UNINTERRUPTIBLE)
835 * @timeout: the pre-initialized and started timer, or NULL for none
836 * @waiter: the pre-initialized rt_mutex_waiter
837 *
838 * lock->wait_lock must be held by the caller.
839 */
840static int __sched
841__rt_mutex_slowlock(struct rt_mutex *lock, int state,
842 struct hrtimer_sleeper *timeout,
843 struct rt_mutex_waiter *waiter)
844{
845 int ret = 0;
846
847 for (;;) {
848 /* Try to acquire the lock: */
849 if (try_to_take_rt_mutex(lock, current, waiter))
850 break;
851
852 /*
853 * TASK_INTERRUPTIBLE checks for signals and
854 * timeout. Ignored otherwise.
855 */
856 if (unlikely(state == TASK_INTERRUPTIBLE)) {
857 /* Signal pending? */
858 if (signal_pending(current))
859 ret = -EINTR;
860 if (timeout && !timeout->task)
861 ret = -ETIMEDOUT;
862 if (ret)
863 break;
864 }
865
866 raw_spin_unlock(&lock->wait_lock);
867
868 debug_rt_mutex_print_deadlock(waiter);
869
870 schedule_rt_mutex(lock);
871
872 raw_spin_lock(&lock->wait_lock);
873 set_current_state(state);
874 }
875
876 return ret;
877}
878
879static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
880 struct rt_mutex_waiter *w)
881{
882 /*
883 * If the result is not -EDEADLOCK or the caller requested
884 * deadlock detection, nothing to do here.
885 */
886 if (res != -EDEADLOCK || detect_deadlock)
887 return;
888
889 /*
890 * Yell lowdly and stop the task right here.
891 */
892 rt_mutex_print_deadlock(w);
893 while (1) {
894 set_current_state(TASK_INTERRUPTIBLE);
895 schedule();
896 }
897}
898
899/*
900 * Slow path lock function:
901 */
902static int __sched
903rt_mutex_slowlock(struct rt_mutex *lock, int state,
904 struct hrtimer_sleeper *timeout,
905 int detect_deadlock)
906{
907 struct rt_mutex_waiter waiter;
908 int ret = 0;
909
910 debug_rt_mutex_init_waiter(&waiter);
911 RB_CLEAR_NODE(&waiter.pi_tree_entry);
912 RB_CLEAR_NODE(&waiter.tree_entry);
913
914 raw_spin_lock(&lock->wait_lock);
915
916 /* Try to acquire the lock again: */
917 if (try_to_take_rt_mutex(lock, current, NULL)) {
918 raw_spin_unlock(&lock->wait_lock);
919 return 0;
920 }
921
922 set_current_state(state);
923
924 /* Setup the timer, when timeout != NULL */
925 if (unlikely(timeout)) {
926 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
927 if (!hrtimer_active(&timeout->timer))
928 timeout->task = NULL;
929 }
930
931 ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
932
933 if (likely(!ret))
934 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
935
936 set_current_state(TASK_RUNNING);
937
938 if (unlikely(ret)) {
939 remove_waiter(lock, &waiter);
940 rt_mutex_handle_deadlock(ret, detect_deadlock, &waiter);
941 }
942
943 /*
944 * try_to_take_rt_mutex() sets the waiter bit
945 * unconditionally. We might have to fix that up.
946 */
947 fixup_rt_mutex_waiters(lock);
948
949 raw_spin_unlock(&lock->wait_lock);
950
951 /* Remove pending timer: */
952 if (unlikely(timeout))
953 hrtimer_cancel(&timeout->timer);
954
955 debug_rt_mutex_free_waiter(&waiter);
956
957 return ret;
958}
959
960/*
961 * Slow path try-lock function:
962 */
963static inline int
964rt_mutex_slowtrylock(struct rt_mutex *lock)
965{
966 int ret = 0;
967
968 raw_spin_lock(&lock->wait_lock);
969
970 if (likely(rt_mutex_owner(lock) != current)) {
971
972 ret = try_to_take_rt_mutex(lock, current, NULL);
973 /*
974 * try_to_take_rt_mutex() sets the lock waiters
975 * bit unconditionally. Clean this up.
976 */
977 fixup_rt_mutex_waiters(lock);
978 }
979
980 raw_spin_unlock(&lock->wait_lock);
981
982 return ret;
983}
984
985/*
986 * Slow path to release a rt-mutex:
987 */
988static void __sched
989rt_mutex_slowunlock(struct rt_mutex *lock)
990{
991 raw_spin_lock(&lock->wait_lock);
992
993 debug_rt_mutex_unlock(lock);
994
995 rt_mutex_deadlock_account_unlock(current);
996
997 /*
998 * We must be careful here if the fast path is enabled. If we
999 * have no waiters queued we cannot set owner to NULL here
1000 * because of:
1001 *
1002 * foo->lock->owner = NULL;
1003 * rtmutex_lock(foo->lock); <- fast path
1004 * free = atomic_dec_and_test(foo->refcnt);
1005 * rtmutex_unlock(foo->lock); <- fast path
1006 * if (free)
1007 * kfree(foo);
1008 * raw_spin_unlock(foo->lock->wait_lock);
1009 *
1010 * So for the fastpath enabled kernel:
1011 *
1012 * Nothing can set the waiters bit as long as we hold
1013 * lock->wait_lock. So we do the following sequence:
1014 *
1015 * owner = rt_mutex_owner(lock);
1016 * clear_rt_mutex_waiters(lock);
1017 * raw_spin_unlock(&lock->wait_lock);
1018 * if (cmpxchg(&lock->owner, owner, 0) == owner)
1019 * return;
1020 * goto retry;
1021 *
1022 * The fastpath disabled variant is simple as all access to
1023 * lock->owner is serialized by lock->wait_lock:
1024 *
1025 * lock->owner = NULL;
1026 * raw_spin_unlock(&lock->wait_lock);
1027 */
1028 while (!rt_mutex_has_waiters(lock)) {
1029 /* Drops lock->wait_lock ! */
1030 if (unlock_rt_mutex_safe(lock) == true)
1031 return;
1032 /* Relock the rtmutex and try again */
1033 raw_spin_lock(&lock->wait_lock);
1034 }
1035
1036 /*
1037 * The wakeup next waiter path does not suffer from the above
1038 * race. See the comments there.
1039 */
1040 wakeup_next_waiter(lock);
1041
1042 raw_spin_unlock(&lock->wait_lock);
1043
1044 /* Undo pi boosting if necessary: */
1045 rt_mutex_adjust_prio(current);
1046}
1047
1048/*
1049 * debug aware fast / slowpath lock,trylock,unlock
1050 *
1051 * The atomic acquire/release ops are compiled away, when either the
1052 * architecture does not support cmpxchg or when debugging is enabled.
1053 */
1054static inline int
1055rt_mutex_fastlock(struct rt_mutex *lock, int state,
1056 int detect_deadlock,
1057 int (*slowfn)(struct rt_mutex *lock, int state,
1058 struct hrtimer_sleeper *timeout,
1059 int detect_deadlock))
1060{
1061 if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1062 rt_mutex_deadlock_account_lock(lock, current);
1063 return 0;
1064 } else
1065 return slowfn(lock, state, NULL, detect_deadlock);
1066}
1067
1068static inline int
1069rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1070 struct hrtimer_sleeper *timeout, int detect_deadlock,
1071 int (*slowfn)(struct rt_mutex *lock, int state,
1072 struct hrtimer_sleeper *timeout,
1073 int detect_deadlock))
1074{
1075 if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1076 rt_mutex_deadlock_account_lock(lock, current);
1077 return 0;
1078 } else
1079 return slowfn(lock, state, timeout, detect_deadlock);
1080}
1081
1082static inline int
1083rt_mutex_fasttrylock(struct rt_mutex *lock,
1084 int (*slowfn)(struct rt_mutex *lock))
1085{
1086 if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
1087 rt_mutex_deadlock_account_lock(lock, current);
1088 return 1;
1089 }
1090 return slowfn(lock);
1091}
1092
1093static inline void
1094rt_mutex_fastunlock(struct rt_mutex *lock,
1095 void (*slowfn)(struct rt_mutex *lock))
1096{
1097 if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
1098 rt_mutex_deadlock_account_unlock(current);
1099 else
1100 slowfn(lock);
1101}
1102
1103/**
1104 * rt_mutex_lock - lock a rt_mutex
1105 *
1106 * @lock: the rt_mutex to be locked
1107 */
1108void __sched rt_mutex_lock(struct rt_mutex *lock)
1109{
1110 might_sleep();
1111
1112 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
1113}
1114EXPORT_SYMBOL_GPL(rt_mutex_lock);
1115
1116/**
1117 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1118 *
1119 * @lock: the rt_mutex to be locked
1120 * @detect_deadlock: deadlock detection on/off
1121 *
1122 * Returns:
1123 * 0 on success
1124 * -EINTR when interrupted by a signal
1125 * -EDEADLK when the lock would deadlock (when deadlock detection is on)
1126 */
1127int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
1128 int detect_deadlock)
1129{
1130 might_sleep();
1131
1132 return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
1133 detect_deadlock, rt_mutex_slowlock);
1134}
1135EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1136
1137/**
1138 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1139 * the timeout structure is provided
1140 * by the caller
1141 *
1142 * @lock: the rt_mutex to be locked
1143 * @timeout: timeout structure or NULL (no timeout)
1144 * @detect_deadlock: deadlock detection on/off
1145 *
1146 * Returns:
1147 * 0 on success
1148 * -EINTR when interrupted by a signal
1149 * -ETIMEDOUT when the timeout expired
1150 * -EDEADLK when the lock would deadlock (when deadlock detection is on)
1151 */
1152int
1153rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
1154 int detect_deadlock)
1155{
1156 might_sleep();
1157
1158 return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1159 detect_deadlock, rt_mutex_slowlock);
1160}
1161EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1162
1163/**
1164 * rt_mutex_trylock - try to lock a rt_mutex
1165 *
1166 * @lock: the rt_mutex to be locked
1167 *
1168 * Returns 1 on success and 0 on contention
1169 */
1170int __sched rt_mutex_trylock(struct rt_mutex *lock)
1171{
1172 return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1173}
1174EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1175
1176/**
1177 * rt_mutex_unlock - unlock a rt_mutex
1178 *
1179 * @lock: the rt_mutex to be unlocked
1180 */
1181void __sched rt_mutex_unlock(struct rt_mutex *lock)
1182{
1183 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1184}
1185EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1186
1187/**
1188 * rt_mutex_destroy - mark a mutex unusable
1189 * @lock: the mutex to be destroyed
1190 *
1191 * This function marks the mutex uninitialized, and any subsequent
1192 * use of the mutex is forbidden. The mutex must not be locked when
1193 * this function is called.
1194 */
1195void rt_mutex_destroy(struct rt_mutex *lock)
1196{
1197 WARN_ON(rt_mutex_is_locked(lock));
1198#ifdef CONFIG_DEBUG_RT_MUTEXES
1199 lock->magic = NULL;
1200#endif
1201}
1202
1203EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1204
1205/**
1206 * __rt_mutex_init - initialize the rt lock
1207 *
1208 * @lock: the rt lock to be initialized
1209 *
1210 * Initialize the rt lock to unlocked state.
1211 *
1212 * Initializing of a locked rt lock is not allowed
1213 */
1214void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1215{
1216 lock->owner = NULL;
1217 raw_spin_lock_init(&lock->wait_lock);
1218 lock->waiters = RB_ROOT;
1219 lock->waiters_leftmost = NULL;
1220
1221 debug_rt_mutex_init(lock, name);
1222}
1223EXPORT_SYMBOL_GPL(__rt_mutex_init);
1224
1225/**
1226 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1227 * proxy owner
1228 *
1229 * @lock: the rt_mutex to be locked
1230 * @proxy_owner:the task to set as owner
1231 *
1232 * No locking. Caller has to do serializing itself
1233 * Special API call for PI-futex support
1234 */
1235void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1236 struct task_struct *proxy_owner)
1237{
1238 __rt_mutex_init(lock, NULL);
1239 debug_rt_mutex_proxy_lock(lock, proxy_owner);
1240 rt_mutex_set_owner(lock, proxy_owner);
1241 rt_mutex_deadlock_account_lock(lock, proxy_owner);
1242}
1243
1244/**
1245 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1246 *
1247 * @lock: the rt_mutex to be locked
1248 *
1249 * No locking. Caller has to do serializing itself
1250 * Special API call for PI-futex support
1251 */
1252void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1253 struct task_struct *proxy_owner)
1254{
1255 debug_rt_mutex_proxy_unlock(lock);
1256 rt_mutex_set_owner(lock, NULL);
1257 rt_mutex_deadlock_account_unlock(proxy_owner);
1258}
1259
1260/**
1261 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1262 * @lock: the rt_mutex to take
1263 * @waiter: the pre-initialized rt_mutex_waiter
1264 * @task: the task to prepare
1265 * @detect_deadlock: perform deadlock detection (1) or not (0)
1266 *
1267 * Returns:
1268 * 0 - task blocked on lock
1269 * 1 - acquired the lock for task, caller should wake it up
1270 * <0 - error
1271 *
1272 * Special API call for FUTEX_REQUEUE_PI support.
1273 */
1274int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1275 struct rt_mutex_waiter *waiter,
1276 struct task_struct *task, int detect_deadlock)
1277{
1278 int ret;
1279
1280 raw_spin_lock(&lock->wait_lock);
1281
1282 if (try_to_take_rt_mutex(lock, task, NULL)) {
1283 raw_spin_unlock(&lock->wait_lock);
1284 return 1;
1285 }
1286
1287 /* We enforce deadlock detection for futexes */
1288 ret = task_blocks_on_rt_mutex(lock, waiter, task, 1);
1289
1290 if (ret && !rt_mutex_owner(lock)) {
1291 /*
1292 * Reset the return value. We might have
1293 * returned with -EDEADLK and the owner
1294 * released the lock while we were walking the
1295 * pi chain. Let the waiter sort it out.
1296 */
1297 ret = 0;
1298 }
1299
1300 if (unlikely(ret))
1301 remove_waiter(lock, waiter);
1302
1303 raw_spin_unlock(&lock->wait_lock);
1304
1305 debug_rt_mutex_print_deadlock(waiter);
1306
1307 return ret;
1308}
1309
1310/**
1311 * rt_mutex_next_owner - return the next owner of the lock
1312 *
1313 * @lock: the rt lock query
1314 *
1315 * Returns the next owner of the lock or NULL
1316 *
1317 * Caller has to serialize against other accessors to the lock
1318 * itself.
1319 *
1320 * Special API call for PI-futex support
1321 */
1322struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1323{
1324 if (!rt_mutex_has_waiters(lock))
1325 return NULL;
1326
1327 return rt_mutex_top_waiter(lock)->task;
1328}
1329
1330/**
1331 * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1332 * @lock: the rt_mutex we were woken on
1333 * @to: the timeout, null if none. hrtimer should already have
1334 * been started.
1335 * @waiter: the pre-initialized rt_mutex_waiter
1336 * @detect_deadlock: perform deadlock detection (1) or not (0)
1337 *
1338 * Complete the lock acquisition started our behalf by another thread.
1339 *
1340 * Returns:
1341 * 0 - success
1342 * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1343 *
1344 * Special API call for PI-futex requeue support
1345 */
1346int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1347 struct hrtimer_sleeper *to,
1348 struct rt_mutex_waiter *waiter,
1349 int detect_deadlock)
1350{
1351 int ret;
1352
1353 raw_spin_lock(&lock->wait_lock);
1354
1355 set_current_state(TASK_INTERRUPTIBLE);
1356
1357 ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1358
1359 set_current_state(TASK_RUNNING);
1360
1361 if (unlikely(ret))
1362 remove_waiter(lock, waiter);
1363
1364 /*
1365 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1366 * have to fix that up.
1367 */
1368 fixup_rt_mutex_waiters(lock);
1369
1370 raw_spin_unlock(&lock->wait_lock);
1371
1372 return ret;
1373}