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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 * Adaptive Spinlocks:
12 * Copyright (C) 2008 Novell, Inc., Gregory Haskins, Sven Dietrich,
13 * and Peter Morreale,
14 * Adaptive Spinlocks simplification:
15 * Copyright (C) 2008 Red Hat, Inc., Steven Rostedt <srostedt@redhat.com>
16 *
17 * See Documentation/locking/rt-mutex-design.rst for details.
18 */
19#include <linux/sched.h>
20#include <linux/sched/debug.h>
21#include <linux/sched/deadline.h>
22#include <linux/sched/signal.h>
23#include <linux/sched/rt.h>
24#include <linux/sched/wake_q.h>
25#include <linux/ww_mutex.h>
26
27#include <trace/events/lock.h>
28
29#include "rtmutex_common.h"
30
31#ifndef WW_RT
32# define build_ww_mutex() (false)
33# define ww_container_of(rtm) NULL
34
35static inline int __ww_mutex_add_waiter(struct rt_mutex_waiter *waiter,
36 struct rt_mutex *lock,
37 struct ww_acquire_ctx *ww_ctx)
38{
39 return 0;
40}
41
42static inline void __ww_mutex_check_waiters(struct rt_mutex *lock,
43 struct ww_acquire_ctx *ww_ctx)
44{
45}
46
47static inline void ww_mutex_lock_acquired(struct ww_mutex *lock,
48 struct ww_acquire_ctx *ww_ctx)
49{
50}
51
52static inline int __ww_mutex_check_kill(struct rt_mutex *lock,
53 struct rt_mutex_waiter *waiter,
54 struct ww_acquire_ctx *ww_ctx)
55{
56 return 0;
57}
58
59#else
60# define build_ww_mutex() (true)
61# define ww_container_of(rtm) container_of(rtm, struct ww_mutex, base)
62# include "ww_mutex.h"
63#endif
64
65/*
66 * lock->owner state tracking:
67 *
68 * lock->owner holds the task_struct pointer of the owner. Bit 0
69 * is used to keep track of the "lock has waiters" state.
70 *
71 * owner bit0
72 * NULL 0 lock is free (fast acquire possible)
73 * NULL 1 lock is free and has waiters and the top waiter
74 * is going to take the lock*
75 * taskpointer 0 lock is held (fast release possible)
76 * taskpointer 1 lock is held and has waiters**
77 *
78 * The fast atomic compare exchange based acquire and release is only
79 * possible when bit 0 of lock->owner is 0.
80 *
81 * (*) It also can be a transitional state when grabbing the lock
82 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
83 * we need to set the bit0 before looking at the lock, and the owner may be
84 * NULL in this small time, hence this can be a transitional state.
85 *
86 * (**) There is a small time when bit 0 is set but there are no
87 * waiters. This can happen when grabbing the lock in the slow path.
88 * To prevent a cmpxchg of the owner releasing the lock, we need to
89 * set this bit before looking at the lock.
90 */
91
92static __always_inline struct task_struct *
93rt_mutex_owner_encode(struct rt_mutex_base *lock, struct task_struct *owner)
94{
95 unsigned long val = (unsigned long)owner;
96
97 if (rt_mutex_has_waiters(lock))
98 val |= RT_MUTEX_HAS_WAITERS;
99
100 return (struct task_struct *)val;
101}
102
103static __always_inline void
104rt_mutex_set_owner(struct rt_mutex_base *lock, struct task_struct *owner)
105{
106 /*
107 * lock->wait_lock is held but explicit acquire semantics are needed
108 * for a new lock owner so WRITE_ONCE is insufficient.
109 */
110 xchg_acquire(&lock->owner, rt_mutex_owner_encode(lock, owner));
111}
112
113static __always_inline void rt_mutex_clear_owner(struct rt_mutex_base *lock)
114{
115 /* lock->wait_lock is held so the unlock provides release semantics. */
116 WRITE_ONCE(lock->owner, rt_mutex_owner_encode(lock, NULL));
117}
118
119static __always_inline void clear_rt_mutex_waiters(struct rt_mutex_base *lock)
120{
121 lock->owner = (struct task_struct *)
122 ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
123}
124
125static __always_inline void
126fixup_rt_mutex_waiters(struct rt_mutex_base *lock, bool acquire_lock)
127{
128 unsigned long owner, *p = (unsigned long *) &lock->owner;
129
130 if (rt_mutex_has_waiters(lock))
131 return;
132
133 /*
134 * The rbtree has no waiters enqueued, now make sure that the
135 * lock->owner still has the waiters bit set, otherwise the
136 * following can happen:
137 *
138 * CPU 0 CPU 1 CPU2
139 * l->owner=T1
140 * rt_mutex_lock(l)
141 * lock(l->lock)
142 * l->owner = T1 | HAS_WAITERS;
143 * enqueue(T2)
144 * boost()
145 * unlock(l->lock)
146 * block()
147 *
148 * rt_mutex_lock(l)
149 * lock(l->lock)
150 * l->owner = T1 | HAS_WAITERS;
151 * enqueue(T3)
152 * boost()
153 * unlock(l->lock)
154 * block()
155 * signal(->T2) signal(->T3)
156 * lock(l->lock)
157 * dequeue(T2)
158 * deboost()
159 * unlock(l->lock)
160 * lock(l->lock)
161 * dequeue(T3)
162 * ==> wait list is empty
163 * deboost()
164 * unlock(l->lock)
165 * lock(l->lock)
166 * fixup_rt_mutex_waiters()
167 * if (wait_list_empty(l) {
168 * l->owner = owner
169 * owner = l->owner & ~HAS_WAITERS;
170 * ==> l->owner = T1
171 * }
172 * lock(l->lock)
173 * rt_mutex_unlock(l) fixup_rt_mutex_waiters()
174 * if (wait_list_empty(l) {
175 * owner = l->owner & ~HAS_WAITERS;
176 * cmpxchg(l->owner, T1, NULL)
177 * ===> Success (l->owner = NULL)
178 *
179 * l->owner = owner
180 * ==> l->owner = T1
181 * }
182 *
183 * With the check for the waiter bit in place T3 on CPU2 will not
184 * overwrite. All tasks fiddling with the waiters bit are
185 * serialized by l->lock, so nothing else can modify the waiters
186 * bit. If the bit is set then nothing can change l->owner either
187 * so the simple RMW is safe. The cmpxchg() will simply fail if it
188 * happens in the middle of the RMW because the waiters bit is
189 * still set.
190 */
191 owner = READ_ONCE(*p);
192 if (owner & RT_MUTEX_HAS_WAITERS) {
193 /*
194 * See rt_mutex_set_owner() and rt_mutex_clear_owner() on
195 * why xchg_acquire() is used for updating owner for
196 * locking and WRITE_ONCE() for unlocking.
197 *
198 * WRITE_ONCE() would work for the acquire case too, but
199 * in case that the lock acquisition failed it might
200 * force other lockers into the slow path unnecessarily.
201 */
202 if (acquire_lock)
203 xchg_acquire(p, owner & ~RT_MUTEX_HAS_WAITERS);
204 else
205 WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
206 }
207}
208
209/*
210 * We can speed up the acquire/release, if there's no debugging state to be
211 * set up.
212 */
213#ifndef CONFIG_DEBUG_RT_MUTEXES
214static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
215 struct task_struct *old,
216 struct task_struct *new)
217{
218 return try_cmpxchg_acquire(&lock->owner, &old, new);
219}
220
221static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
222 struct task_struct *old,
223 struct task_struct *new)
224{
225 return try_cmpxchg_release(&lock->owner, &old, new);
226}
227
228/*
229 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
230 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
231 * relaxed semantics suffice.
232 */
233static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
234{
235 unsigned long owner, *p = (unsigned long *) &lock->owner;
236
237 do {
238 owner = *p;
239 } while (cmpxchg_relaxed(p, owner,
240 owner | RT_MUTEX_HAS_WAITERS) != owner);
241
242 /*
243 * The cmpxchg loop above is relaxed to avoid back-to-back ACQUIRE
244 * operations in the event of contention. Ensure the successful
245 * cmpxchg is visible.
246 */
247 smp_mb__after_atomic();
248}
249
250/*
251 * Safe fastpath aware unlock:
252 * 1) Clear the waiters bit
253 * 2) Drop lock->wait_lock
254 * 3) Try to unlock the lock with cmpxchg
255 */
256static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
257 unsigned long flags)
258 __releases(lock->wait_lock)
259{
260 struct task_struct *owner = rt_mutex_owner(lock);
261
262 clear_rt_mutex_waiters(lock);
263 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
264 /*
265 * If a new waiter comes in between the unlock and the cmpxchg
266 * we have two situations:
267 *
268 * unlock(wait_lock);
269 * lock(wait_lock);
270 * cmpxchg(p, owner, 0) == owner
271 * mark_rt_mutex_waiters(lock);
272 * acquire(lock);
273 * or:
274 *
275 * unlock(wait_lock);
276 * lock(wait_lock);
277 * mark_rt_mutex_waiters(lock);
278 *
279 * cmpxchg(p, owner, 0) != owner
280 * enqueue_waiter();
281 * unlock(wait_lock);
282 * lock(wait_lock);
283 * wake waiter();
284 * unlock(wait_lock);
285 * lock(wait_lock);
286 * acquire(lock);
287 */
288 return rt_mutex_cmpxchg_release(lock, owner, NULL);
289}
290
291#else
292static __always_inline bool rt_mutex_cmpxchg_acquire(struct rt_mutex_base *lock,
293 struct task_struct *old,
294 struct task_struct *new)
295{
296 return false;
297
298}
299
300static __always_inline bool rt_mutex_cmpxchg_release(struct rt_mutex_base *lock,
301 struct task_struct *old,
302 struct task_struct *new)
303{
304 return false;
305}
306
307static __always_inline void mark_rt_mutex_waiters(struct rt_mutex_base *lock)
308{
309 lock->owner = (struct task_struct *)
310 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
311}
312
313/*
314 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
315 */
316static __always_inline bool unlock_rt_mutex_safe(struct rt_mutex_base *lock,
317 unsigned long flags)
318 __releases(lock->wait_lock)
319{
320 lock->owner = NULL;
321 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
322 return true;
323}
324#endif
325
326static __always_inline int __waiter_prio(struct task_struct *task)
327{
328 int prio = task->prio;
329
330 if (!rt_prio(prio))
331 return DEFAULT_PRIO;
332
333 return prio;
334}
335
336static __always_inline void
337waiter_update_prio(struct rt_mutex_waiter *waiter, struct task_struct *task)
338{
339 waiter->prio = __waiter_prio(task);
340 waiter->deadline = task->dl.deadline;
341}
342
343/*
344 * Only use with rt_mutex_waiter_{less,equal}()
345 */
346#define task_to_waiter(p) \
347 &(struct rt_mutex_waiter){ .prio = __waiter_prio(p), .deadline = (p)->dl.deadline }
348
349static __always_inline int rt_mutex_waiter_less(struct rt_mutex_waiter *left,
350 struct rt_mutex_waiter *right)
351{
352 if (left->prio < right->prio)
353 return 1;
354
355 /*
356 * If both waiters have dl_prio(), we check the deadlines of the
357 * associated tasks.
358 * If left waiter has a dl_prio(), and we didn't return 1 above,
359 * then right waiter has a dl_prio() too.
360 */
361 if (dl_prio(left->prio))
362 return dl_time_before(left->deadline, right->deadline);
363
364 return 0;
365}
366
367static __always_inline int rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
368 struct rt_mutex_waiter *right)
369{
370 if (left->prio != right->prio)
371 return 0;
372
373 /*
374 * If both waiters have dl_prio(), we check the deadlines of the
375 * associated tasks.
376 * If left waiter has a dl_prio(), and we didn't return 0 above,
377 * then right waiter has a dl_prio() too.
378 */
379 if (dl_prio(left->prio))
380 return left->deadline == right->deadline;
381
382 return 1;
383}
384
385static inline bool rt_mutex_steal(struct rt_mutex_waiter *waiter,
386 struct rt_mutex_waiter *top_waiter)
387{
388 if (rt_mutex_waiter_less(waiter, top_waiter))
389 return true;
390
391#ifdef RT_MUTEX_BUILD_SPINLOCKS
392 /*
393 * Note that RT tasks are excluded from same priority (lateral)
394 * steals to prevent the introduction of an unbounded latency.
395 */
396 if (rt_prio(waiter->prio) || dl_prio(waiter->prio))
397 return false;
398
399 return rt_mutex_waiter_equal(waiter, top_waiter);
400#else
401 return false;
402#endif
403}
404
405#define __node_2_waiter(node) \
406 rb_entry((node), struct rt_mutex_waiter, tree_entry)
407
408static __always_inline bool __waiter_less(struct rb_node *a, const struct rb_node *b)
409{
410 struct rt_mutex_waiter *aw = __node_2_waiter(a);
411 struct rt_mutex_waiter *bw = __node_2_waiter(b);
412
413 if (rt_mutex_waiter_less(aw, bw))
414 return 1;
415
416 if (!build_ww_mutex())
417 return 0;
418
419 if (rt_mutex_waiter_less(bw, aw))
420 return 0;
421
422 /* NOTE: relies on waiter->ww_ctx being set before insertion */
423 if (aw->ww_ctx) {
424 if (!bw->ww_ctx)
425 return 1;
426
427 return (signed long)(aw->ww_ctx->stamp -
428 bw->ww_ctx->stamp) < 0;
429 }
430
431 return 0;
432}
433
434static __always_inline void
435rt_mutex_enqueue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
436{
437 rb_add_cached(&waiter->tree_entry, &lock->waiters, __waiter_less);
438}
439
440static __always_inline void
441rt_mutex_dequeue(struct rt_mutex_base *lock, struct rt_mutex_waiter *waiter)
442{
443 if (RB_EMPTY_NODE(&waiter->tree_entry))
444 return;
445
446 rb_erase_cached(&waiter->tree_entry, &lock->waiters);
447 RB_CLEAR_NODE(&waiter->tree_entry);
448}
449
450#define __node_2_pi_waiter(node) \
451 rb_entry((node), struct rt_mutex_waiter, pi_tree_entry)
452
453static __always_inline bool
454__pi_waiter_less(struct rb_node *a, const struct rb_node *b)
455{
456 return rt_mutex_waiter_less(__node_2_pi_waiter(a), __node_2_pi_waiter(b));
457}
458
459static __always_inline void
460rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
461{
462 rb_add_cached(&waiter->pi_tree_entry, &task->pi_waiters, __pi_waiter_less);
463}
464
465static __always_inline void
466rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
467{
468 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
469 return;
470
471 rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
472 RB_CLEAR_NODE(&waiter->pi_tree_entry);
473}
474
475static __always_inline void rt_mutex_adjust_prio(struct task_struct *p)
476{
477 struct task_struct *pi_task = NULL;
478
479 lockdep_assert_held(&p->pi_lock);
480
481 if (task_has_pi_waiters(p))
482 pi_task = task_top_pi_waiter(p)->task;
483
484 rt_mutex_setprio(p, pi_task);
485}
486
487/* RT mutex specific wake_q wrappers */
488static __always_inline void rt_mutex_wake_q_add_task(struct rt_wake_q_head *wqh,
489 struct task_struct *task,
490 unsigned int wake_state)
491{
492 if (IS_ENABLED(CONFIG_PREEMPT_RT) && wake_state == TASK_RTLOCK_WAIT) {
493 if (IS_ENABLED(CONFIG_PROVE_LOCKING))
494 WARN_ON_ONCE(wqh->rtlock_task);
495 get_task_struct(task);
496 wqh->rtlock_task = task;
497 } else {
498 wake_q_add(&wqh->head, task);
499 }
500}
501
502static __always_inline void rt_mutex_wake_q_add(struct rt_wake_q_head *wqh,
503 struct rt_mutex_waiter *w)
504{
505 rt_mutex_wake_q_add_task(wqh, w->task, w->wake_state);
506}
507
508static __always_inline void rt_mutex_wake_up_q(struct rt_wake_q_head *wqh)
509{
510 if (IS_ENABLED(CONFIG_PREEMPT_RT) && wqh->rtlock_task) {
511 wake_up_state(wqh->rtlock_task, TASK_RTLOCK_WAIT);
512 put_task_struct(wqh->rtlock_task);
513 wqh->rtlock_task = NULL;
514 }
515
516 if (!wake_q_empty(&wqh->head))
517 wake_up_q(&wqh->head);
518
519 /* Pairs with preempt_disable() in mark_wakeup_next_waiter() */
520 preempt_enable();
521}
522
523/*
524 * Deadlock detection is conditional:
525 *
526 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
527 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
528 *
529 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
530 * conducted independent of the detect argument.
531 *
532 * If the waiter argument is NULL this indicates the deboost path and
533 * deadlock detection is disabled independent of the detect argument
534 * and the config settings.
535 */
536static __always_inline bool
537rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
538 enum rtmutex_chainwalk chwalk)
539{
540 if (IS_ENABLED(CONFIG_DEBUG_RT_MUTEXES))
541 return waiter != NULL;
542 return chwalk == RT_MUTEX_FULL_CHAINWALK;
543}
544
545static __always_inline struct rt_mutex_base *task_blocked_on_lock(struct task_struct *p)
546{
547 return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
548}
549
550/*
551 * Adjust the priority chain. Also used for deadlock detection.
552 * Decreases task's usage by one - may thus free the task.
553 *
554 * @task: the task owning the mutex (owner) for which a chain walk is
555 * probably needed
556 * @chwalk: do we have to carry out deadlock detection?
557 * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
558 * things for a task that has just got its priority adjusted, and
559 * is waiting on a mutex)
560 * @next_lock: the mutex on which the owner of @orig_lock was blocked before
561 * we dropped its pi_lock. Is never dereferenced, only used for
562 * comparison to detect lock chain changes.
563 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
564 * its priority to the mutex owner (can be NULL in the case
565 * depicted above or if the top waiter is gone away and we are
566 * actually deboosting the owner)
567 * @top_task: the current top waiter
568 *
569 * Returns 0 or -EDEADLK.
570 *
571 * Chain walk basics and protection scope
572 *
573 * [R] refcount on task
574 * [P] task->pi_lock held
575 * [L] rtmutex->wait_lock held
576 *
577 * Step Description Protected by
578 * function arguments:
579 * @task [R]
580 * @orig_lock if != NULL @top_task is blocked on it
581 * @next_lock Unprotected. Cannot be
582 * dereferenced. Only used for
583 * comparison.
584 * @orig_waiter if != NULL @top_task is blocked on it
585 * @top_task current, or in case of proxy
586 * locking protected by calling
587 * code
588 * again:
589 * loop_sanity_check();
590 * retry:
591 * [1] lock(task->pi_lock); [R] acquire [P]
592 * [2] waiter = task->pi_blocked_on; [P]
593 * [3] check_exit_conditions_1(); [P]
594 * [4] lock = waiter->lock; [P]
595 * [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
596 * unlock(task->pi_lock); release [P]
597 * goto retry;
598 * }
599 * [6] check_exit_conditions_2(); [P] + [L]
600 * [7] requeue_lock_waiter(lock, waiter); [P] + [L]
601 * [8] unlock(task->pi_lock); release [P]
602 * put_task_struct(task); release [R]
603 * [9] check_exit_conditions_3(); [L]
604 * [10] task = owner(lock); [L]
605 * get_task_struct(task); [L] acquire [R]
606 * lock(task->pi_lock); [L] acquire [P]
607 * [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
608 * [12] check_exit_conditions_4(); [P] + [L]
609 * [13] unlock(task->pi_lock); release [P]
610 * unlock(lock->wait_lock); release [L]
611 * goto again;
612 */
613static int __sched rt_mutex_adjust_prio_chain(struct task_struct *task,
614 enum rtmutex_chainwalk chwalk,
615 struct rt_mutex_base *orig_lock,
616 struct rt_mutex_base *next_lock,
617 struct rt_mutex_waiter *orig_waiter,
618 struct task_struct *top_task)
619{
620 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
621 struct rt_mutex_waiter *prerequeue_top_waiter;
622 int ret = 0, depth = 0;
623 struct rt_mutex_base *lock;
624 bool detect_deadlock;
625 bool requeue = true;
626
627 detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
628
629 /*
630 * The (de)boosting is a step by step approach with a lot of
631 * pitfalls. We want this to be preemptible and we want hold a
632 * maximum of two locks per step. So we have to check
633 * carefully whether things change under us.
634 */
635 again:
636 /*
637 * We limit the lock chain length for each invocation.
638 */
639 if (++depth > max_lock_depth) {
640 static int prev_max;
641
642 /*
643 * Print this only once. If the admin changes the limit,
644 * print a new message when reaching the limit again.
645 */
646 if (prev_max != max_lock_depth) {
647 prev_max = max_lock_depth;
648 printk(KERN_WARNING "Maximum lock depth %d reached "
649 "task: %s (%d)\n", max_lock_depth,
650 top_task->comm, task_pid_nr(top_task));
651 }
652 put_task_struct(task);
653
654 return -EDEADLK;
655 }
656
657 /*
658 * We are fully preemptible here and only hold the refcount on
659 * @task. So everything can have changed under us since the
660 * caller or our own code below (goto retry/again) dropped all
661 * locks.
662 */
663 retry:
664 /*
665 * [1] Task cannot go away as we did a get_task() before !
666 */
667 raw_spin_lock_irq(&task->pi_lock);
668
669 /*
670 * [2] Get the waiter on which @task is blocked on.
671 */
672 waiter = task->pi_blocked_on;
673
674 /*
675 * [3] check_exit_conditions_1() protected by task->pi_lock.
676 */
677
678 /*
679 * Check whether the end of the boosting chain has been
680 * reached or the state of the chain has changed while we
681 * dropped the locks.
682 */
683 if (!waiter)
684 goto out_unlock_pi;
685
686 /*
687 * Check the orig_waiter state. After we dropped the locks,
688 * the previous owner of the lock might have released the lock.
689 */
690 if (orig_waiter && !rt_mutex_owner(orig_lock))
691 goto out_unlock_pi;
692
693 /*
694 * We dropped all locks after taking a refcount on @task, so
695 * the task might have moved on in the lock chain or even left
696 * the chain completely and blocks now on an unrelated lock or
697 * on @orig_lock.
698 *
699 * We stored the lock on which @task was blocked in @next_lock,
700 * so we can detect the chain change.
701 */
702 if (next_lock != waiter->lock)
703 goto out_unlock_pi;
704
705 /*
706 * There could be 'spurious' loops in the lock graph due to ww_mutex,
707 * consider:
708 *
709 * P1: A, ww_A, ww_B
710 * P2: ww_B, ww_A
711 * P3: A
712 *
713 * P3 should not return -EDEADLK because it gets trapped in the cycle
714 * created by P1 and P2 (which will resolve -- and runs into
715 * max_lock_depth above). Therefore disable detect_deadlock such that
716 * the below termination condition can trigger once all relevant tasks
717 * are boosted.
718 *
719 * Even when we start with ww_mutex we can disable deadlock detection,
720 * since we would supress a ww_mutex induced deadlock at [6] anyway.
721 * Supressing it here however is not sufficient since we might still
722 * hit [6] due to adjustment driven iteration.
723 *
724 * NOTE: if someone were to create a deadlock between 2 ww_classes we'd
725 * utterly fail to report it; lockdep should.
726 */
727 if (IS_ENABLED(CONFIG_PREEMPT_RT) && waiter->ww_ctx && detect_deadlock)
728 detect_deadlock = false;
729
730 /*
731 * Drop out, when the task has no waiters. Note,
732 * top_waiter can be NULL, when we are in the deboosting
733 * mode!
734 */
735 if (top_waiter) {
736 if (!task_has_pi_waiters(task))
737 goto out_unlock_pi;
738 /*
739 * If deadlock detection is off, we stop here if we
740 * are not the top pi waiter of the task. If deadlock
741 * detection is enabled we continue, but stop the
742 * requeueing in the chain walk.
743 */
744 if (top_waiter != task_top_pi_waiter(task)) {
745 if (!detect_deadlock)
746 goto out_unlock_pi;
747 else
748 requeue = false;
749 }
750 }
751
752 /*
753 * If the waiter priority is the same as the task priority
754 * then there is no further priority adjustment necessary. If
755 * deadlock detection is off, we stop the chain walk. If its
756 * enabled we continue, but stop the requeueing in the chain
757 * walk.
758 */
759 if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
760 if (!detect_deadlock)
761 goto out_unlock_pi;
762 else
763 requeue = false;
764 }
765
766 /*
767 * [4] Get the next lock
768 */
769 lock = waiter->lock;
770 /*
771 * [5] We need to trylock here as we are holding task->pi_lock,
772 * which is the reverse lock order versus the other rtmutex
773 * operations.
774 */
775 if (!raw_spin_trylock(&lock->wait_lock)) {
776 raw_spin_unlock_irq(&task->pi_lock);
777 cpu_relax();
778 goto retry;
779 }
780
781 /*
782 * [6] check_exit_conditions_2() protected by task->pi_lock and
783 * lock->wait_lock.
784 *
785 * Deadlock detection. If the lock is the same as the original
786 * lock which caused us to walk the lock chain or if the
787 * current lock is owned by the task which initiated the chain
788 * walk, we detected a deadlock.
789 */
790 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
791 ret = -EDEADLK;
792
793 /*
794 * When the deadlock is due to ww_mutex; also see above. Don't
795 * report the deadlock and instead let the ww_mutex wound/die
796 * logic pick which of the contending threads gets -EDEADLK.
797 *
798 * NOTE: assumes the cycle only contains a single ww_class; any
799 * other configuration and we fail to report; also, see
800 * lockdep.
801 */
802 if (IS_ENABLED(CONFIG_PREEMPT_RT) && orig_waiter && orig_waiter->ww_ctx)
803 ret = 0;
804
805 raw_spin_unlock(&lock->wait_lock);
806 goto out_unlock_pi;
807 }
808
809 /*
810 * If we just follow the lock chain for deadlock detection, no
811 * need to do all the requeue operations. To avoid a truckload
812 * of conditionals around the various places below, just do the
813 * minimum chain walk checks.
814 */
815 if (!requeue) {
816 /*
817 * No requeue[7] here. Just release @task [8]
818 */
819 raw_spin_unlock(&task->pi_lock);
820 put_task_struct(task);
821
822 /*
823 * [9] check_exit_conditions_3 protected by lock->wait_lock.
824 * If there is no owner of the lock, end of chain.
825 */
826 if (!rt_mutex_owner(lock)) {
827 raw_spin_unlock_irq(&lock->wait_lock);
828 return 0;
829 }
830
831 /* [10] Grab the next task, i.e. owner of @lock */
832 task = get_task_struct(rt_mutex_owner(lock));
833 raw_spin_lock(&task->pi_lock);
834
835 /*
836 * No requeue [11] here. We just do deadlock detection.
837 *
838 * [12] Store whether owner is blocked
839 * itself. Decision is made after dropping the locks
840 */
841 next_lock = task_blocked_on_lock(task);
842 /*
843 * Get the top waiter for the next iteration
844 */
845 top_waiter = rt_mutex_top_waiter(lock);
846
847 /* [13] Drop locks */
848 raw_spin_unlock(&task->pi_lock);
849 raw_spin_unlock_irq(&lock->wait_lock);
850
851 /* If owner is not blocked, end of chain. */
852 if (!next_lock)
853 goto out_put_task;
854 goto again;
855 }
856
857 /*
858 * Store the current top waiter before doing the requeue
859 * operation on @lock. We need it for the boost/deboost
860 * decision below.
861 */
862 prerequeue_top_waiter = rt_mutex_top_waiter(lock);
863
864 /* [7] Requeue the waiter in the lock waiter tree. */
865 rt_mutex_dequeue(lock, waiter);
866
867 /*
868 * Update the waiter prio fields now that we're dequeued.
869 *
870 * These values can have changed through either:
871 *
872 * sys_sched_set_scheduler() / sys_sched_setattr()
873 *
874 * or
875 *
876 * DL CBS enforcement advancing the effective deadline.
877 *
878 * Even though pi_waiters also uses these fields, and that tree is only
879 * updated in [11], we can do this here, since we hold [L], which
880 * serializes all pi_waiters access and rb_erase() does not care about
881 * the values of the node being removed.
882 */
883 waiter_update_prio(waiter, task);
884
885 rt_mutex_enqueue(lock, waiter);
886
887 /* [8] Release the task */
888 raw_spin_unlock(&task->pi_lock);
889 put_task_struct(task);
890
891 /*
892 * [9] check_exit_conditions_3 protected by lock->wait_lock.
893 *
894 * We must abort the chain walk if there is no lock owner even
895 * in the dead lock detection case, as we have nothing to
896 * follow here. This is the end of the chain we are walking.
897 */
898 if (!rt_mutex_owner(lock)) {
899 /*
900 * If the requeue [7] above changed the top waiter,
901 * then we need to wake the new top waiter up to try
902 * to get the lock.
903 */
904 top_waiter = rt_mutex_top_waiter(lock);
905 if (prerequeue_top_waiter != top_waiter)
906 wake_up_state(top_waiter->task, top_waiter->wake_state);
907 raw_spin_unlock_irq(&lock->wait_lock);
908 return 0;
909 }
910
911 /* [10] Grab the next task, i.e. the owner of @lock */
912 task = get_task_struct(rt_mutex_owner(lock));
913 raw_spin_lock(&task->pi_lock);
914
915 /* [11] requeue the pi waiters if necessary */
916 if (waiter == rt_mutex_top_waiter(lock)) {
917 /*
918 * The waiter became the new top (highest priority)
919 * waiter on the lock. Replace the previous top waiter
920 * in the owner tasks pi waiters tree with this waiter
921 * and adjust the priority of the owner.
922 */
923 rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
924 rt_mutex_enqueue_pi(task, waiter);
925 rt_mutex_adjust_prio(task);
926
927 } else if (prerequeue_top_waiter == waiter) {
928 /*
929 * The waiter was the top waiter on the lock, but is
930 * no longer the top priority waiter. Replace waiter in
931 * the owner tasks pi waiters tree with the new top
932 * (highest priority) waiter and adjust the priority
933 * of the owner.
934 * The new top waiter is stored in @waiter so that
935 * @waiter == @top_waiter evaluates to true below and
936 * we continue to deboost the rest of the chain.
937 */
938 rt_mutex_dequeue_pi(task, waiter);
939 waiter = rt_mutex_top_waiter(lock);
940 rt_mutex_enqueue_pi(task, waiter);
941 rt_mutex_adjust_prio(task);
942 } else {
943 /*
944 * Nothing changed. No need to do any priority
945 * adjustment.
946 */
947 }
948
949 /*
950 * [12] check_exit_conditions_4() protected by task->pi_lock
951 * and lock->wait_lock. The actual decisions are made after we
952 * dropped the locks.
953 *
954 * Check whether the task which owns the current lock is pi
955 * blocked itself. If yes we store a pointer to the lock for
956 * the lock chain change detection above. After we dropped
957 * task->pi_lock next_lock cannot be dereferenced anymore.
958 */
959 next_lock = task_blocked_on_lock(task);
960 /*
961 * Store the top waiter of @lock for the end of chain walk
962 * decision below.
963 */
964 top_waiter = rt_mutex_top_waiter(lock);
965
966 /* [13] Drop the locks */
967 raw_spin_unlock(&task->pi_lock);
968 raw_spin_unlock_irq(&lock->wait_lock);
969
970 /*
971 * Make the actual exit decisions [12], based on the stored
972 * values.
973 *
974 * We reached the end of the lock chain. Stop right here. No
975 * point to go back just to figure that out.
976 */
977 if (!next_lock)
978 goto out_put_task;
979
980 /*
981 * If the current waiter is not the top waiter on the lock,
982 * then we can stop the chain walk here if we are not in full
983 * deadlock detection mode.
984 */
985 if (!detect_deadlock && waiter != top_waiter)
986 goto out_put_task;
987
988 goto again;
989
990 out_unlock_pi:
991 raw_spin_unlock_irq(&task->pi_lock);
992 out_put_task:
993 put_task_struct(task);
994
995 return ret;
996}
997
998/*
999 * Try to take an rt-mutex
1000 *
1001 * Must be called with lock->wait_lock held and interrupts disabled
1002 *
1003 * @lock: The lock to be acquired.
1004 * @task: The task which wants to acquire the lock
1005 * @waiter: The waiter that is queued to the lock's wait tree if the
1006 * callsite called task_blocked_on_lock(), otherwise NULL
1007 */
1008static int __sched
1009try_to_take_rt_mutex(struct rt_mutex_base *lock, struct task_struct *task,
1010 struct rt_mutex_waiter *waiter)
1011{
1012 lockdep_assert_held(&lock->wait_lock);
1013
1014 /*
1015 * Before testing whether we can acquire @lock, we set the
1016 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
1017 * other tasks which try to modify @lock into the slow path
1018 * and they serialize on @lock->wait_lock.
1019 *
1020 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
1021 * as explained at the top of this file if and only if:
1022 *
1023 * - There is a lock owner. The caller must fixup the
1024 * transient state if it does a trylock or leaves the lock
1025 * function due to a signal or timeout.
1026 *
1027 * - @task acquires the lock and there are no other
1028 * waiters. This is undone in rt_mutex_set_owner(@task) at
1029 * the end of this function.
1030 */
1031 mark_rt_mutex_waiters(lock);
1032
1033 /*
1034 * If @lock has an owner, give up.
1035 */
1036 if (rt_mutex_owner(lock))
1037 return 0;
1038
1039 /*
1040 * If @waiter != NULL, @task has already enqueued the waiter
1041 * into @lock waiter tree. If @waiter == NULL then this is a
1042 * trylock attempt.
1043 */
1044 if (waiter) {
1045 struct rt_mutex_waiter *top_waiter = rt_mutex_top_waiter(lock);
1046
1047 /*
1048 * If waiter is the highest priority waiter of @lock,
1049 * or allowed to steal it, take it over.
1050 */
1051 if (waiter == top_waiter || rt_mutex_steal(waiter, top_waiter)) {
1052 /*
1053 * We can acquire the lock. Remove the waiter from the
1054 * lock waiters tree.
1055 */
1056 rt_mutex_dequeue(lock, waiter);
1057 } else {
1058 return 0;
1059 }
1060 } else {
1061 /*
1062 * If the lock has waiters already we check whether @task is
1063 * eligible to take over the lock.
1064 *
1065 * If there are no other waiters, @task can acquire
1066 * the lock. @task->pi_blocked_on is NULL, so it does
1067 * not need to be dequeued.
1068 */
1069 if (rt_mutex_has_waiters(lock)) {
1070 /* Check whether the trylock can steal it. */
1071 if (!rt_mutex_steal(task_to_waiter(task),
1072 rt_mutex_top_waiter(lock)))
1073 return 0;
1074
1075 /*
1076 * The current top waiter stays enqueued. We
1077 * don't have to change anything in the lock
1078 * waiters order.
1079 */
1080 } else {
1081 /*
1082 * No waiters. Take the lock without the
1083 * pi_lock dance.@task->pi_blocked_on is NULL
1084 * and we have no waiters to enqueue in @task
1085 * pi waiters tree.
1086 */
1087 goto takeit;
1088 }
1089 }
1090
1091 /*
1092 * Clear @task->pi_blocked_on. Requires protection by
1093 * @task->pi_lock. Redundant operation for the @waiter == NULL
1094 * case, but conditionals are more expensive than a redundant
1095 * store.
1096 */
1097 raw_spin_lock(&task->pi_lock);
1098 task->pi_blocked_on = NULL;
1099 /*
1100 * Finish the lock acquisition. @task is the new owner. If
1101 * other waiters exist we have to insert the highest priority
1102 * waiter into @task->pi_waiters tree.
1103 */
1104 if (rt_mutex_has_waiters(lock))
1105 rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
1106 raw_spin_unlock(&task->pi_lock);
1107
1108takeit:
1109 /*
1110 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
1111 * are still waiters or clears it.
1112 */
1113 rt_mutex_set_owner(lock, task);
1114
1115 return 1;
1116}
1117
1118/*
1119 * Task blocks on lock.
1120 *
1121 * Prepare waiter and propagate pi chain
1122 *
1123 * This must be called with lock->wait_lock held and interrupts disabled
1124 */
1125static int __sched task_blocks_on_rt_mutex(struct rt_mutex_base *lock,
1126 struct rt_mutex_waiter *waiter,
1127 struct task_struct *task,
1128 struct ww_acquire_ctx *ww_ctx,
1129 enum rtmutex_chainwalk chwalk)
1130{
1131 struct task_struct *owner = rt_mutex_owner(lock);
1132 struct rt_mutex_waiter *top_waiter = waiter;
1133 struct rt_mutex_base *next_lock;
1134 int chain_walk = 0, res;
1135
1136 lockdep_assert_held(&lock->wait_lock);
1137
1138 /*
1139 * Early deadlock detection. We really don't want the task to
1140 * enqueue on itself just to untangle the mess later. It's not
1141 * only an optimization. We drop the locks, so another waiter
1142 * can come in before the chain walk detects the deadlock. So
1143 * the other will detect the deadlock and return -EDEADLOCK,
1144 * which is wrong, as the other waiter is not in a deadlock
1145 * situation.
1146 *
1147 * Except for ww_mutex, in that case the chain walk must already deal
1148 * with spurious cycles, see the comments at [3] and [6].
1149 */
1150 if (owner == task && !(build_ww_mutex() && ww_ctx))
1151 return -EDEADLK;
1152
1153 raw_spin_lock(&task->pi_lock);
1154 waiter->task = task;
1155 waiter->lock = lock;
1156 waiter_update_prio(waiter, task);
1157
1158 /* Get the top priority waiter on the lock */
1159 if (rt_mutex_has_waiters(lock))
1160 top_waiter = rt_mutex_top_waiter(lock);
1161 rt_mutex_enqueue(lock, waiter);
1162
1163 task->pi_blocked_on = waiter;
1164
1165 raw_spin_unlock(&task->pi_lock);
1166
1167 if (build_ww_mutex() && ww_ctx) {
1168 struct rt_mutex *rtm;
1169
1170 /* Check whether the waiter should back out immediately */
1171 rtm = container_of(lock, struct rt_mutex, rtmutex);
1172 res = __ww_mutex_add_waiter(waiter, rtm, ww_ctx);
1173 if (res) {
1174 raw_spin_lock(&task->pi_lock);
1175 rt_mutex_dequeue(lock, waiter);
1176 task->pi_blocked_on = NULL;
1177 raw_spin_unlock(&task->pi_lock);
1178 return res;
1179 }
1180 }
1181
1182 if (!owner)
1183 return 0;
1184
1185 raw_spin_lock(&owner->pi_lock);
1186 if (waiter == rt_mutex_top_waiter(lock)) {
1187 rt_mutex_dequeue_pi(owner, top_waiter);
1188 rt_mutex_enqueue_pi(owner, waiter);
1189
1190 rt_mutex_adjust_prio(owner);
1191 if (owner->pi_blocked_on)
1192 chain_walk = 1;
1193 } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
1194 chain_walk = 1;
1195 }
1196
1197 /* Store the lock on which owner is blocked or NULL */
1198 next_lock = task_blocked_on_lock(owner);
1199
1200 raw_spin_unlock(&owner->pi_lock);
1201 /*
1202 * Even if full deadlock detection is on, if the owner is not
1203 * blocked itself, we can avoid finding this out in the chain
1204 * walk.
1205 */
1206 if (!chain_walk || !next_lock)
1207 return 0;
1208
1209 /*
1210 * The owner can't disappear while holding a lock,
1211 * so the owner struct is protected by wait_lock.
1212 * Gets dropped in rt_mutex_adjust_prio_chain()!
1213 */
1214 get_task_struct(owner);
1215
1216 raw_spin_unlock_irq(&lock->wait_lock);
1217
1218 res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1219 next_lock, waiter, task);
1220
1221 raw_spin_lock_irq(&lock->wait_lock);
1222
1223 return res;
1224}
1225
1226/*
1227 * Remove the top waiter from the current tasks pi waiter tree and
1228 * queue it up.
1229 *
1230 * Called with lock->wait_lock held and interrupts disabled.
1231 */
1232static void __sched mark_wakeup_next_waiter(struct rt_wake_q_head *wqh,
1233 struct rt_mutex_base *lock)
1234{
1235 struct rt_mutex_waiter *waiter;
1236
1237 raw_spin_lock(¤t->pi_lock);
1238
1239 waiter = rt_mutex_top_waiter(lock);
1240
1241 /*
1242 * Remove it from current->pi_waiters and deboost.
1243 *
1244 * We must in fact deboost here in order to ensure we call
1245 * rt_mutex_setprio() to update p->pi_top_task before the
1246 * task unblocks.
1247 */
1248 rt_mutex_dequeue_pi(current, waiter);
1249 rt_mutex_adjust_prio(current);
1250
1251 /*
1252 * As we are waking up the top waiter, and the waiter stays
1253 * queued on the lock until it gets the lock, this lock
1254 * obviously has waiters. Just set the bit here and this has
1255 * the added benefit of forcing all new tasks into the
1256 * slow path making sure no task of lower priority than
1257 * the top waiter can steal this lock.
1258 */
1259 lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1260
1261 /*
1262 * We deboosted before waking the top waiter task such that we don't
1263 * run two tasks with the 'same' priority (and ensure the
1264 * p->pi_top_task pointer points to a blocked task). This however can
1265 * lead to priority inversion if we would get preempted after the
1266 * deboost but before waking our donor task, hence the preempt_disable()
1267 * before unlock.
1268 *
1269 * Pairs with preempt_enable() in rt_mutex_wake_up_q();
1270 */
1271 preempt_disable();
1272 rt_mutex_wake_q_add(wqh, waiter);
1273 raw_spin_unlock(¤t->pi_lock);
1274}
1275
1276static int __sched __rt_mutex_slowtrylock(struct rt_mutex_base *lock)
1277{
1278 int ret = try_to_take_rt_mutex(lock, current, NULL);
1279
1280 /*
1281 * try_to_take_rt_mutex() sets the lock waiters bit
1282 * unconditionally. Clean this up.
1283 */
1284 fixup_rt_mutex_waiters(lock, true);
1285
1286 return ret;
1287}
1288
1289/*
1290 * Slow path try-lock function:
1291 */
1292static int __sched rt_mutex_slowtrylock(struct rt_mutex_base *lock)
1293{
1294 unsigned long flags;
1295 int ret;
1296
1297 /*
1298 * If the lock already has an owner we fail to get the lock.
1299 * This can be done without taking the @lock->wait_lock as
1300 * it is only being read, and this is a trylock anyway.
1301 */
1302 if (rt_mutex_owner(lock))
1303 return 0;
1304
1305 /*
1306 * The mutex has currently no owner. Lock the wait lock and try to
1307 * acquire the lock. We use irqsave here to support early boot calls.
1308 */
1309 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1310
1311 ret = __rt_mutex_slowtrylock(lock);
1312
1313 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1314
1315 return ret;
1316}
1317
1318static __always_inline int __rt_mutex_trylock(struct rt_mutex_base *lock)
1319{
1320 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1321 return 1;
1322
1323 return rt_mutex_slowtrylock(lock);
1324}
1325
1326/*
1327 * Slow path to release a rt-mutex.
1328 */
1329static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
1330{
1331 DEFINE_RT_WAKE_Q(wqh);
1332 unsigned long flags;
1333
1334 /* irqsave required to support early boot calls */
1335 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1336
1337 debug_rt_mutex_unlock(lock);
1338
1339 /*
1340 * We must be careful here if the fast path is enabled. If we
1341 * have no waiters queued we cannot set owner to NULL here
1342 * because of:
1343 *
1344 * foo->lock->owner = NULL;
1345 * rtmutex_lock(foo->lock); <- fast path
1346 * free = atomic_dec_and_test(foo->refcnt);
1347 * rtmutex_unlock(foo->lock); <- fast path
1348 * if (free)
1349 * kfree(foo);
1350 * raw_spin_unlock(foo->lock->wait_lock);
1351 *
1352 * So for the fastpath enabled kernel:
1353 *
1354 * Nothing can set the waiters bit as long as we hold
1355 * lock->wait_lock. So we do the following sequence:
1356 *
1357 * owner = rt_mutex_owner(lock);
1358 * clear_rt_mutex_waiters(lock);
1359 * raw_spin_unlock(&lock->wait_lock);
1360 * if (cmpxchg(&lock->owner, owner, 0) == owner)
1361 * return;
1362 * goto retry;
1363 *
1364 * The fastpath disabled variant is simple as all access to
1365 * lock->owner is serialized by lock->wait_lock:
1366 *
1367 * lock->owner = NULL;
1368 * raw_spin_unlock(&lock->wait_lock);
1369 */
1370 while (!rt_mutex_has_waiters(lock)) {
1371 /* Drops lock->wait_lock ! */
1372 if (unlock_rt_mutex_safe(lock, flags) == true)
1373 return;
1374 /* Relock the rtmutex and try again */
1375 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1376 }
1377
1378 /*
1379 * The wakeup next waiter path does not suffer from the above
1380 * race. See the comments there.
1381 *
1382 * Queue the next waiter for wakeup once we release the wait_lock.
1383 */
1384 mark_wakeup_next_waiter(&wqh, lock);
1385 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1386
1387 rt_mutex_wake_up_q(&wqh);
1388}
1389
1390static __always_inline void __rt_mutex_unlock(struct rt_mutex_base *lock)
1391{
1392 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1393 return;
1394
1395 rt_mutex_slowunlock(lock);
1396}
1397
1398#ifdef CONFIG_SMP
1399static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
1400 struct rt_mutex_waiter *waiter,
1401 struct task_struct *owner)
1402{
1403 bool res = true;
1404
1405 rcu_read_lock();
1406 for (;;) {
1407 /* If owner changed, trylock again. */
1408 if (owner != rt_mutex_owner(lock))
1409 break;
1410 /*
1411 * Ensure that @owner is dereferenced after checking that
1412 * the lock owner still matches @owner. If that fails,
1413 * @owner might point to freed memory. If it still matches,
1414 * the rcu_read_lock() ensures the memory stays valid.
1415 */
1416 barrier();
1417 /*
1418 * Stop spinning when:
1419 * - the lock owner has been scheduled out
1420 * - current is not longer the top waiter
1421 * - current is requested to reschedule (redundant
1422 * for CONFIG_PREEMPT_RCU=y)
1423 * - the VCPU on which owner runs is preempted
1424 */
1425 if (!owner_on_cpu(owner) || need_resched() ||
1426 !rt_mutex_waiter_is_top_waiter(lock, waiter)) {
1427 res = false;
1428 break;
1429 }
1430 cpu_relax();
1431 }
1432 rcu_read_unlock();
1433 return res;
1434}
1435#else
1436static bool rtmutex_spin_on_owner(struct rt_mutex_base *lock,
1437 struct rt_mutex_waiter *waiter,
1438 struct task_struct *owner)
1439{
1440 return false;
1441}
1442#endif
1443
1444#ifdef RT_MUTEX_BUILD_MUTEX
1445/*
1446 * Functions required for:
1447 * - rtmutex, futex on all kernels
1448 * - mutex and rwsem substitutions on RT kernels
1449 */
1450
1451/*
1452 * Remove a waiter from a lock and give up
1453 *
1454 * Must be called with lock->wait_lock held and interrupts disabled. It must
1455 * have just failed to try_to_take_rt_mutex().
1456 */
1457static void __sched remove_waiter(struct rt_mutex_base *lock,
1458 struct rt_mutex_waiter *waiter)
1459{
1460 bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1461 struct task_struct *owner = rt_mutex_owner(lock);
1462 struct rt_mutex_base *next_lock;
1463
1464 lockdep_assert_held(&lock->wait_lock);
1465
1466 raw_spin_lock(¤t->pi_lock);
1467 rt_mutex_dequeue(lock, waiter);
1468 current->pi_blocked_on = NULL;
1469 raw_spin_unlock(¤t->pi_lock);
1470
1471 /*
1472 * Only update priority if the waiter was the highest priority
1473 * waiter of the lock and there is an owner to update.
1474 */
1475 if (!owner || !is_top_waiter)
1476 return;
1477
1478 raw_spin_lock(&owner->pi_lock);
1479
1480 rt_mutex_dequeue_pi(owner, waiter);
1481
1482 if (rt_mutex_has_waiters(lock))
1483 rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1484
1485 rt_mutex_adjust_prio(owner);
1486
1487 /* Store the lock on which owner is blocked or NULL */
1488 next_lock = task_blocked_on_lock(owner);
1489
1490 raw_spin_unlock(&owner->pi_lock);
1491
1492 /*
1493 * Don't walk the chain, if the owner task is not blocked
1494 * itself.
1495 */
1496 if (!next_lock)
1497 return;
1498
1499 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1500 get_task_struct(owner);
1501
1502 raw_spin_unlock_irq(&lock->wait_lock);
1503
1504 rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1505 next_lock, NULL, current);
1506
1507 raw_spin_lock_irq(&lock->wait_lock);
1508}
1509
1510/**
1511 * rt_mutex_slowlock_block() - Perform the wait-wake-try-to-take loop
1512 * @lock: the rt_mutex to take
1513 * @ww_ctx: WW mutex context pointer
1514 * @state: the state the task should block in (TASK_INTERRUPTIBLE
1515 * or TASK_UNINTERRUPTIBLE)
1516 * @timeout: the pre-initialized and started timer, or NULL for none
1517 * @waiter: the pre-initialized rt_mutex_waiter
1518 *
1519 * Must be called with lock->wait_lock held and interrupts disabled
1520 */
1521static int __sched rt_mutex_slowlock_block(struct rt_mutex_base *lock,
1522 struct ww_acquire_ctx *ww_ctx,
1523 unsigned int state,
1524 struct hrtimer_sleeper *timeout,
1525 struct rt_mutex_waiter *waiter)
1526{
1527 struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
1528 struct task_struct *owner;
1529 int ret = 0;
1530
1531 for (;;) {
1532 /* Try to acquire the lock: */
1533 if (try_to_take_rt_mutex(lock, current, waiter))
1534 break;
1535
1536 if (timeout && !timeout->task) {
1537 ret = -ETIMEDOUT;
1538 break;
1539 }
1540 if (signal_pending_state(state, current)) {
1541 ret = -EINTR;
1542 break;
1543 }
1544
1545 if (build_ww_mutex() && ww_ctx) {
1546 ret = __ww_mutex_check_kill(rtm, waiter, ww_ctx);
1547 if (ret)
1548 break;
1549 }
1550
1551 if (waiter == rt_mutex_top_waiter(lock))
1552 owner = rt_mutex_owner(lock);
1553 else
1554 owner = NULL;
1555 raw_spin_unlock_irq(&lock->wait_lock);
1556
1557 if (!owner || !rtmutex_spin_on_owner(lock, waiter, owner))
1558 schedule();
1559
1560 raw_spin_lock_irq(&lock->wait_lock);
1561 set_current_state(state);
1562 }
1563
1564 __set_current_state(TASK_RUNNING);
1565 return ret;
1566}
1567
1568static void __sched rt_mutex_handle_deadlock(int res, int detect_deadlock,
1569 struct rt_mutex_waiter *w)
1570{
1571 /*
1572 * If the result is not -EDEADLOCK or the caller requested
1573 * deadlock detection, nothing to do here.
1574 */
1575 if (res != -EDEADLOCK || detect_deadlock)
1576 return;
1577
1578 if (build_ww_mutex() && w->ww_ctx)
1579 return;
1580
1581 /*
1582 * Yell loudly and stop the task right here.
1583 */
1584 WARN(1, "rtmutex deadlock detected\n");
1585 while (1) {
1586 set_current_state(TASK_INTERRUPTIBLE);
1587 schedule();
1588 }
1589}
1590
1591/**
1592 * __rt_mutex_slowlock - Locking slowpath invoked with lock::wait_lock held
1593 * @lock: The rtmutex to block lock
1594 * @ww_ctx: WW mutex context pointer
1595 * @state: The task state for sleeping
1596 * @chwalk: Indicator whether full or partial chainwalk is requested
1597 * @waiter: Initializer waiter for blocking
1598 */
1599static int __sched __rt_mutex_slowlock(struct rt_mutex_base *lock,
1600 struct ww_acquire_ctx *ww_ctx,
1601 unsigned int state,
1602 enum rtmutex_chainwalk chwalk,
1603 struct rt_mutex_waiter *waiter)
1604{
1605 struct rt_mutex *rtm = container_of(lock, struct rt_mutex, rtmutex);
1606 struct ww_mutex *ww = ww_container_of(rtm);
1607 int ret;
1608
1609 lockdep_assert_held(&lock->wait_lock);
1610
1611 /* Try to acquire the lock again: */
1612 if (try_to_take_rt_mutex(lock, current, NULL)) {
1613 if (build_ww_mutex() && ww_ctx) {
1614 __ww_mutex_check_waiters(rtm, ww_ctx);
1615 ww_mutex_lock_acquired(ww, ww_ctx);
1616 }
1617 return 0;
1618 }
1619
1620 set_current_state(state);
1621
1622 trace_contention_begin(lock, LCB_F_RT);
1623
1624 ret = task_blocks_on_rt_mutex(lock, waiter, current, ww_ctx, chwalk);
1625 if (likely(!ret))
1626 ret = rt_mutex_slowlock_block(lock, ww_ctx, state, NULL, waiter);
1627
1628 if (likely(!ret)) {
1629 /* acquired the lock */
1630 if (build_ww_mutex() && ww_ctx) {
1631 if (!ww_ctx->is_wait_die)
1632 __ww_mutex_check_waiters(rtm, ww_ctx);
1633 ww_mutex_lock_acquired(ww, ww_ctx);
1634 }
1635 } else {
1636 __set_current_state(TASK_RUNNING);
1637 remove_waiter(lock, waiter);
1638 rt_mutex_handle_deadlock(ret, chwalk, waiter);
1639 }
1640
1641 /*
1642 * try_to_take_rt_mutex() sets the waiter bit
1643 * unconditionally. We might have to fix that up.
1644 */
1645 fixup_rt_mutex_waiters(lock, true);
1646
1647 trace_contention_end(lock, ret);
1648
1649 return ret;
1650}
1651
1652static inline int __rt_mutex_slowlock_locked(struct rt_mutex_base *lock,
1653 struct ww_acquire_ctx *ww_ctx,
1654 unsigned int state)
1655{
1656 struct rt_mutex_waiter waiter;
1657 int ret;
1658
1659 rt_mutex_init_waiter(&waiter);
1660 waiter.ww_ctx = ww_ctx;
1661
1662 ret = __rt_mutex_slowlock(lock, ww_ctx, state, RT_MUTEX_MIN_CHAINWALK,
1663 &waiter);
1664
1665 debug_rt_mutex_free_waiter(&waiter);
1666 return ret;
1667}
1668
1669/*
1670 * rt_mutex_slowlock - Locking slowpath invoked when fast path fails
1671 * @lock: The rtmutex to block lock
1672 * @ww_ctx: WW mutex context pointer
1673 * @state: The task state for sleeping
1674 */
1675static int __sched rt_mutex_slowlock(struct rt_mutex_base *lock,
1676 struct ww_acquire_ctx *ww_ctx,
1677 unsigned int state)
1678{
1679 unsigned long flags;
1680 int ret;
1681
1682 /*
1683 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1684 * be called in early boot if the cmpxchg() fast path is disabled
1685 * (debug, no architecture support). In this case we will acquire the
1686 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1687 * enable interrupts in that early boot case. So we need to use the
1688 * irqsave/restore variants.
1689 */
1690 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1691 ret = __rt_mutex_slowlock_locked(lock, ww_ctx, state);
1692 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1693
1694 return ret;
1695}
1696
1697static __always_inline int __rt_mutex_lock(struct rt_mutex_base *lock,
1698 unsigned int state)
1699{
1700 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1701 return 0;
1702
1703 return rt_mutex_slowlock(lock, NULL, state);
1704}
1705#endif /* RT_MUTEX_BUILD_MUTEX */
1706
1707#ifdef RT_MUTEX_BUILD_SPINLOCKS
1708/*
1709 * Functions required for spin/rw_lock substitution on RT kernels
1710 */
1711
1712/**
1713 * rtlock_slowlock_locked - Slow path lock acquisition for RT locks
1714 * @lock: The underlying RT mutex
1715 */
1716static void __sched rtlock_slowlock_locked(struct rt_mutex_base *lock)
1717{
1718 struct rt_mutex_waiter waiter;
1719 struct task_struct *owner;
1720
1721 lockdep_assert_held(&lock->wait_lock);
1722
1723 if (try_to_take_rt_mutex(lock, current, NULL))
1724 return;
1725
1726 rt_mutex_init_rtlock_waiter(&waiter);
1727
1728 /* Save current state and set state to TASK_RTLOCK_WAIT */
1729 current_save_and_set_rtlock_wait_state();
1730
1731 trace_contention_begin(lock, LCB_F_RT);
1732
1733 task_blocks_on_rt_mutex(lock, &waiter, current, NULL, RT_MUTEX_MIN_CHAINWALK);
1734
1735 for (;;) {
1736 /* Try to acquire the lock again */
1737 if (try_to_take_rt_mutex(lock, current, &waiter))
1738 break;
1739
1740 if (&waiter == rt_mutex_top_waiter(lock))
1741 owner = rt_mutex_owner(lock);
1742 else
1743 owner = NULL;
1744 raw_spin_unlock_irq(&lock->wait_lock);
1745
1746 if (!owner || !rtmutex_spin_on_owner(lock, &waiter, owner))
1747 schedule_rtlock();
1748
1749 raw_spin_lock_irq(&lock->wait_lock);
1750 set_current_state(TASK_RTLOCK_WAIT);
1751 }
1752
1753 /* Restore the task state */
1754 current_restore_rtlock_saved_state();
1755
1756 /*
1757 * try_to_take_rt_mutex() sets the waiter bit unconditionally.
1758 * We might have to fix that up:
1759 */
1760 fixup_rt_mutex_waiters(lock, true);
1761 debug_rt_mutex_free_waiter(&waiter);
1762
1763 trace_contention_end(lock, 0);
1764}
1765
1766static __always_inline void __sched rtlock_slowlock(struct rt_mutex_base *lock)
1767{
1768 unsigned long flags;
1769
1770 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1771 rtlock_slowlock_locked(lock);
1772 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1773}
1774
1775#endif /* RT_MUTEX_BUILD_SPINLOCKS */