projects/linux·blob v3.15 · 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#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(&current->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(&current->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(&current->pi_lock, flags);
651 rt_mutex_dequeue(lock, waiter);
652 current->pi_blocked_on = NULL;
653 raw_spin_unlock_irqrestore(&current->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}