projects/linux·blob v4.19 · 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/locking/rt-mutex-design.txt for details.
12 */
13#include <linux/spinlock.h>
14#include <linux/export.h>
15#include <linux/sched/signal.h>
16#include <linux/sched/rt.h>
17#include <linux/sched/deadline.h>
18#include <linux/sched/wake_q.h>
19#include <linux/sched/debug.h>
20#include <linux/timer.h>
21
22#include "rtmutex_common.h"
23
24/*
25 * lock->owner state tracking:
26 *
27 * lock->owner holds the task_struct pointer of the owner. Bit 0
28 * is used to keep track of the "lock has waiters" state.
29 *
30 * owner bit0
31 * NULL 0 lock is free (fast acquire possible)
32 * NULL 1 lock is free and has waiters and the top waiter
33 * is going to take the lock*
34 * taskpointer 0 lock is held (fast release possible)
35 * taskpointer 1 lock is held and has waiters**
36 *
37 * The fast atomic compare exchange based acquire and release is only
38 * possible when bit 0 of lock->owner is 0.
39 *
40 * (*) It also can be a transitional state when grabbing the lock
41 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
42 * we need to set the bit0 before looking at the lock, and the owner may be
43 * NULL in this small time, hence this can be a transitional state.
44 *
45 * (**) There is a small time when bit 0 is set but there are no
46 * waiters. This can happen when grabbing the lock in the slow path.
47 * To prevent a cmpxchg of the owner releasing the lock, we need to
48 * set this bit before looking at the lock.
49 */
50
51static void
52rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
53{
54 unsigned long val = (unsigned long)owner;
55
56 if (rt_mutex_has_waiters(lock))
57 val |= RT_MUTEX_HAS_WAITERS;
58
59 lock->owner = (struct task_struct *)val;
60}
61
62static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
63{
64 lock->owner = (struct task_struct *)
65 ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
66}
67
68static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
69{
70 unsigned long owner, *p = (unsigned long *) &lock->owner;
71
72 if (rt_mutex_has_waiters(lock))
73 return;
74
75 /*
76 * The rbtree has no waiters enqueued, now make sure that the
77 * lock->owner still has the waiters bit set, otherwise the
78 * following can happen:
79 *
80 * CPU 0 CPU 1 CPU2
81 * l->owner=T1
82 * rt_mutex_lock(l)
83 * lock(l->lock)
84 * l->owner = T1 | HAS_WAITERS;
85 * enqueue(T2)
86 * boost()
87 * unlock(l->lock)
88 * block()
89 *
90 * rt_mutex_lock(l)
91 * lock(l->lock)
92 * l->owner = T1 | HAS_WAITERS;
93 * enqueue(T3)
94 * boost()
95 * unlock(l->lock)
96 * block()
97 * signal(->T2) signal(->T3)
98 * lock(l->lock)
99 * dequeue(T2)
100 * deboost()
101 * unlock(l->lock)
102 * lock(l->lock)
103 * dequeue(T3)
104 * ==> wait list is empty
105 * deboost()
106 * unlock(l->lock)
107 * lock(l->lock)
108 * fixup_rt_mutex_waiters()
109 * if (wait_list_empty(l) {
110 * l->owner = owner
111 * owner = l->owner & ~HAS_WAITERS;
112 * ==> l->owner = T1
113 * }
114 * lock(l->lock)
115 * rt_mutex_unlock(l) fixup_rt_mutex_waiters()
116 * if (wait_list_empty(l) {
117 * owner = l->owner & ~HAS_WAITERS;
118 * cmpxchg(l->owner, T1, NULL)
119 * ===> Success (l->owner = NULL)
120 *
121 * l->owner = owner
122 * ==> l->owner = T1
123 * }
124 *
125 * With the check for the waiter bit in place T3 on CPU2 will not
126 * overwrite. All tasks fiddling with the waiters bit are
127 * serialized by l->lock, so nothing else can modify the waiters
128 * bit. If the bit is set then nothing can change l->owner either
129 * so the simple RMW is safe. The cmpxchg() will simply fail if it
130 * happens in the middle of the RMW because the waiters bit is
131 * still set.
132 */
133 owner = READ_ONCE(*p);
134 if (owner & RT_MUTEX_HAS_WAITERS)
135 WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
136}
137
138/*
139 * We can speed up the acquire/release, if there's no debugging state to be
140 * set up.
141 */
142#ifndef CONFIG_DEBUG_RT_MUTEXES
143# define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
144# define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
145# define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
146
147/*
148 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
149 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
150 * relaxed semantics suffice.
151 */
152static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
153{
154 unsigned long owner, *p = (unsigned long *) &lock->owner;
155
156 do {
157 owner = *p;
158 } while (cmpxchg_relaxed(p, owner,
159 owner | RT_MUTEX_HAS_WAITERS) != owner);
160}
161
162/*
163 * Safe fastpath aware unlock:
164 * 1) Clear the waiters bit
165 * 2) Drop lock->wait_lock
166 * 3) Try to unlock the lock with cmpxchg
167 */
168static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
169 unsigned long flags)
170 __releases(lock->wait_lock)
171{
172 struct task_struct *owner = rt_mutex_owner(lock);
173
174 clear_rt_mutex_waiters(lock);
175 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
176 /*
177 * If a new waiter comes in between the unlock and the cmpxchg
178 * we have two situations:
179 *
180 * unlock(wait_lock);
181 * lock(wait_lock);
182 * cmpxchg(p, owner, 0) == owner
183 * mark_rt_mutex_waiters(lock);
184 * acquire(lock);
185 * or:
186 *
187 * unlock(wait_lock);
188 * lock(wait_lock);
189 * mark_rt_mutex_waiters(lock);
190 *
191 * cmpxchg(p, owner, 0) != owner
192 * enqueue_waiter();
193 * unlock(wait_lock);
194 * lock(wait_lock);
195 * wake waiter();
196 * unlock(wait_lock);
197 * lock(wait_lock);
198 * acquire(lock);
199 */
200 return rt_mutex_cmpxchg_release(lock, owner, NULL);
201}
202
203#else
204# define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
205# define rt_mutex_cmpxchg_acquire(l,c,n) (0)
206# define rt_mutex_cmpxchg_release(l,c,n) (0)
207
208static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
209{
210 lock->owner = (struct task_struct *)
211 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
212}
213
214/*
215 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
216 */
217static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
218 unsigned long flags)
219 __releases(lock->wait_lock)
220{
221 lock->owner = NULL;
222 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
223 return true;
224}
225#endif
226
227/*
228 * Only use with rt_mutex_waiter_{less,equal}()
229 */
230#define task_to_waiter(p) \
231 &(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }
232
233static inline int
234rt_mutex_waiter_less(struct rt_mutex_waiter *left,
235 struct rt_mutex_waiter *right)
236{
237 if (left->prio < right->prio)
238 return 1;
239
240 /*
241 * If both waiters have dl_prio(), we check the deadlines of the
242 * associated tasks.
243 * If left waiter has a dl_prio(), and we didn't return 1 above,
244 * then right waiter has a dl_prio() too.
245 */
246 if (dl_prio(left->prio))
247 return dl_time_before(left->deadline, right->deadline);
248
249 return 0;
250}
251
252static inline int
253rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
254 struct rt_mutex_waiter *right)
255{
256 if (left->prio != right->prio)
257 return 0;
258
259 /*
260 * If both waiters have dl_prio(), we check the deadlines of the
261 * associated tasks.
262 * If left waiter has a dl_prio(), and we didn't return 0 above,
263 * then right waiter has a dl_prio() too.
264 */
265 if (dl_prio(left->prio))
266 return left->deadline == right->deadline;
267
268 return 1;
269}
270
271static void
272rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
273{
274 struct rb_node **link = &lock->waiters.rb_root.rb_node;
275 struct rb_node *parent = NULL;
276 struct rt_mutex_waiter *entry;
277 bool leftmost = true;
278
279 while (*link) {
280 parent = *link;
281 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
282 if (rt_mutex_waiter_less(waiter, entry)) {
283 link = &parent->rb_left;
284 } else {
285 link = &parent->rb_right;
286 leftmost = false;
287 }
288 }
289
290 rb_link_node(&waiter->tree_entry, parent, link);
291 rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
292}
293
294static void
295rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
296{
297 if (RB_EMPTY_NODE(&waiter->tree_entry))
298 return;
299
300 rb_erase_cached(&waiter->tree_entry, &lock->waiters);
301 RB_CLEAR_NODE(&waiter->tree_entry);
302}
303
304static void
305rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
306{
307 struct rb_node **link = &task->pi_waiters.rb_root.rb_node;
308 struct rb_node *parent = NULL;
309 struct rt_mutex_waiter *entry;
310 bool leftmost = true;
311
312 while (*link) {
313 parent = *link;
314 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
315 if (rt_mutex_waiter_less(waiter, entry)) {
316 link = &parent->rb_left;
317 } else {
318 link = &parent->rb_right;
319 leftmost = false;
320 }
321 }
322
323 rb_link_node(&waiter->pi_tree_entry, parent, link);
324 rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
325}
326
327static void
328rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
329{
330 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
331 return;
332
333 rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
334 RB_CLEAR_NODE(&waiter->pi_tree_entry);
335}
336
337static void rt_mutex_adjust_prio(struct task_struct *p)
338{
339 struct task_struct *pi_task = NULL;
340
341 lockdep_assert_held(&p->pi_lock);
342
343 if (task_has_pi_waiters(p))
344 pi_task = task_top_pi_waiter(p)->task;
345
346 rt_mutex_setprio(p, pi_task);
347}
348
349/*
350 * Deadlock detection is conditional:
351 *
352 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
353 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
354 *
355 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
356 * conducted independent of the detect argument.
357 *
358 * If the waiter argument is NULL this indicates the deboost path and
359 * deadlock detection is disabled independent of the detect argument
360 * and the config settings.
361 */
362static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
363 enum rtmutex_chainwalk chwalk)
364{
365 /*
366 * This is just a wrapper function for the following call,
367 * because debug_rt_mutex_detect_deadlock() smells like a magic
368 * debug feature and I wanted to keep the cond function in the
369 * main source file along with the comments instead of having
370 * two of the same in the headers.
371 */
372 return debug_rt_mutex_detect_deadlock(waiter, chwalk);
373}
374
375/*
376 * Max number of times we'll walk the boosting chain:
377 */
378int max_lock_depth = 1024;
379
380static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
381{
382 return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
383}
384
385/*
386 * Adjust the priority chain. Also used for deadlock detection.
387 * Decreases task's usage by one - may thus free the task.
388 *
389 * @task: the task owning the mutex (owner) for which a chain walk is
390 * probably needed
391 * @chwalk: do we have to carry out deadlock detection?
392 * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
393 * things for a task that has just got its priority adjusted, and
394 * is waiting on a mutex)
395 * @next_lock: the mutex on which the owner of @orig_lock was blocked before
396 * we dropped its pi_lock. Is never dereferenced, only used for
397 * comparison to detect lock chain changes.
398 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
399 * its priority to the mutex owner (can be NULL in the case
400 * depicted above or if the top waiter is gone away and we are
401 * actually deboosting the owner)
402 * @top_task: the current top waiter
403 *
404 * Returns 0 or -EDEADLK.
405 *
406 * Chain walk basics and protection scope
407 *
408 * [R] refcount on task
409 * [P] task->pi_lock held
410 * [L] rtmutex->wait_lock held
411 *
412 * Step Description Protected by
413 * function arguments:
414 * @task [R]
415 * @orig_lock if != NULL @top_task is blocked on it
416 * @next_lock Unprotected. Cannot be
417 * dereferenced. Only used for
418 * comparison.
419 * @orig_waiter if != NULL @top_task is blocked on it
420 * @top_task current, or in case of proxy
421 * locking protected by calling
422 * code
423 * again:
424 * loop_sanity_check();
425 * retry:
426 * [1] lock(task->pi_lock); [R] acquire [P]
427 * [2] waiter = task->pi_blocked_on; [P]
428 * [3] check_exit_conditions_1(); [P]
429 * [4] lock = waiter->lock; [P]
430 * [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
431 * unlock(task->pi_lock); release [P]
432 * goto retry;
433 * }
434 * [6] check_exit_conditions_2(); [P] + [L]
435 * [7] requeue_lock_waiter(lock, waiter); [P] + [L]
436 * [8] unlock(task->pi_lock); release [P]
437 * put_task_struct(task); release [R]
438 * [9] check_exit_conditions_3(); [L]
439 * [10] task = owner(lock); [L]
440 * get_task_struct(task); [L] acquire [R]
441 * lock(task->pi_lock); [L] acquire [P]
442 * [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
443 * [12] check_exit_conditions_4(); [P] + [L]
444 * [13] unlock(task->pi_lock); release [P]
445 * unlock(lock->wait_lock); release [L]
446 * goto again;
447 */
448static int rt_mutex_adjust_prio_chain(struct task_struct *task,
449 enum rtmutex_chainwalk chwalk,
450 struct rt_mutex *orig_lock,
451 struct rt_mutex *next_lock,
452 struct rt_mutex_waiter *orig_waiter,
453 struct task_struct *top_task)
454{
455 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
456 struct rt_mutex_waiter *prerequeue_top_waiter;
457 int ret = 0, depth = 0;
458 struct rt_mutex *lock;
459 bool detect_deadlock;
460 bool requeue = true;
461
462 detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
463
464 /*
465 * The (de)boosting is a step by step approach with a lot of
466 * pitfalls. We want this to be preemptible and we want hold a
467 * maximum of two locks per step. So we have to check
468 * carefully whether things change under us.
469 */
470 again:
471 /*
472 * We limit the lock chain length for each invocation.
473 */
474 if (++depth > max_lock_depth) {
475 static int prev_max;
476
477 /*
478 * Print this only once. If the admin changes the limit,
479 * print a new message when reaching the limit again.
480 */
481 if (prev_max != max_lock_depth) {
482 prev_max = max_lock_depth;
483 printk(KERN_WARNING "Maximum lock depth %d reached "
484 "task: %s (%d)\n", max_lock_depth,
485 top_task->comm, task_pid_nr(top_task));
486 }
487 put_task_struct(task);
488
489 return -EDEADLK;
490 }
491
492 /*
493 * We are fully preemptible here and only hold the refcount on
494 * @task. So everything can have changed under us since the
495 * caller or our own code below (goto retry/again) dropped all
496 * locks.
497 */
498 retry:
499 /*
500 * [1] Task cannot go away as we did a get_task() before !
501 */
502 raw_spin_lock_irq(&task->pi_lock);
503
504 /*
505 * [2] Get the waiter on which @task is blocked on.
506 */
507 waiter = task->pi_blocked_on;
508
509 /*
510 * [3] check_exit_conditions_1() protected by task->pi_lock.
511 */
512
513 /*
514 * Check whether the end of the boosting chain has been
515 * reached or the state of the chain has changed while we
516 * dropped the locks.
517 */
518 if (!waiter)
519 goto out_unlock_pi;
520
521 /*
522 * Check the orig_waiter state. After we dropped the locks,
523 * the previous owner of the lock might have released the lock.
524 */
525 if (orig_waiter && !rt_mutex_owner(orig_lock))
526 goto out_unlock_pi;
527
528 /*
529 * We dropped all locks after taking a refcount on @task, so
530 * the task might have moved on in the lock chain or even left
531 * the chain completely and blocks now on an unrelated lock or
532 * on @orig_lock.
533 *
534 * We stored the lock on which @task was blocked in @next_lock,
535 * so we can detect the chain change.
536 */
537 if (next_lock != waiter->lock)
538 goto out_unlock_pi;
539
540 /*
541 * Drop out, when the task has no waiters. Note,
542 * top_waiter can be NULL, when we are in the deboosting
543 * mode!
544 */
545 if (top_waiter) {
546 if (!task_has_pi_waiters(task))
547 goto out_unlock_pi;
548 /*
549 * If deadlock detection is off, we stop here if we
550 * are not the top pi waiter of the task. If deadlock
551 * detection is enabled we continue, but stop the
552 * requeueing in the chain walk.
553 */
554 if (top_waiter != task_top_pi_waiter(task)) {
555 if (!detect_deadlock)
556 goto out_unlock_pi;
557 else
558 requeue = false;
559 }
560 }
561
562 /*
563 * If the waiter priority is the same as the task priority
564 * then there is no further priority adjustment necessary. If
565 * deadlock detection is off, we stop the chain walk. If its
566 * enabled we continue, but stop the requeueing in the chain
567 * walk.
568 */
569 if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
570 if (!detect_deadlock)
571 goto out_unlock_pi;
572 else
573 requeue = false;
574 }
575
576 /*
577 * [4] Get the next lock
578 */
579 lock = waiter->lock;
580 /*
581 * [5] We need to trylock here as we are holding task->pi_lock,
582 * which is the reverse lock order versus the other rtmutex
583 * operations.
584 */
585 if (!raw_spin_trylock(&lock->wait_lock)) {
586 raw_spin_unlock_irq(&task->pi_lock);
587 cpu_relax();
588 goto retry;
589 }
590
591 /*
592 * [6] check_exit_conditions_2() protected by task->pi_lock and
593 * lock->wait_lock.
594 *
595 * Deadlock detection. If the lock is the same as the original
596 * lock which caused us to walk the lock chain or if the
597 * current lock is owned by the task which initiated the chain
598 * walk, we detected a deadlock.
599 */
600 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
601 debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
602 raw_spin_unlock(&lock->wait_lock);
603 ret = -EDEADLK;
604 goto out_unlock_pi;
605 }
606
607 /*
608 * If we just follow the lock chain for deadlock detection, no
609 * need to do all the requeue operations. To avoid a truckload
610 * of conditionals around the various places below, just do the
611 * minimum chain walk checks.
612 */
613 if (!requeue) {
614 /*
615 * No requeue[7] here. Just release @task [8]
616 */
617 raw_spin_unlock(&task->pi_lock);
618 put_task_struct(task);
619
620 /*
621 * [9] check_exit_conditions_3 protected by lock->wait_lock.
622 * If there is no owner of the lock, end of chain.
623 */
624 if (!rt_mutex_owner(lock)) {
625 raw_spin_unlock_irq(&lock->wait_lock);
626 return 0;
627 }
628
629 /* [10] Grab the next task, i.e. owner of @lock */
630 task = rt_mutex_owner(lock);
631 get_task_struct(task);
632 raw_spin_lock(&task->pi_lock);
633
634 /*
635 * No requeue [11] here. We just do deadlock detection.
636 *
637 * [12] Store whether owner is blocked
638 * itself. Decision is made after dropping the locks
639 */
640 next_lock = task_blocked_on_lock(task);
641 /*
642 * Get the top waiter for the next iteration
643 */
644 top_waiter = rt_mutex_top_waiter(lock);
645
646 /* [13] Drop locks */
647 raw_spin_unlock(&task->pi_lock);
648 raw_spin_unlock_irq(&lock->wait_lock);
649
650 /* If owner is not blocked, end of chain. */
651 if (!next_lock)
652 goto out_put_task;
653 goto again;
654 }
655
656 /*
657 * Store the current top waiter before doing the requeue
658 * operation on @lock. We need it for the boost/deboost
659 * decision below.
660 */
661 prerequeue_top_waiter = rt_mutex_top_waiter(lock);
662
663 /* [7] Requeue the waiter in the lock waiter tree. */
664 rt_mutex_dequeue(lock, waiter);
665
666 /*
667 * Update the waiter prio fields now that we're dequeued.
668 *
669 * These values can have changed through either:
670 *
671 * sys_sched_set_scheduler() / sys_sched_setattr()
672 *
673 * or
674 *
675 * DL CBS enforcement advancing the effective deadline.
676 *
677 * Even though pi_waiters also uses these fields, and that tree is only
678 * updated in [11], we can do this here, since we hold [L], which
679 * serializes all pi_waiters access and rb_erase() does not care about
680 * the values of the node being removed.
681 */
682 waiter->prio = task->prio;
683 waiter->deadline = task->dl.deadline;
684
685 rt_mutex_enqueue(lock, waiter);
686
687 /* [8] Release the task */
688 raw_spin_unlock(&task->pi_lock);
689 put_task_struct(task);
690
691 /*
692 * [9] check_exit_conditions_3 protected by lock->wait_lock.
693 *
694 * We must abort the chain walk if there is no lock owner even
695 * in the dead lock detection case, as we have nothing to
696 * follow here. This is the end of the chain we are walking.
697 */
698 if (!rt_mutex_owner(lock)) {
699 /*
700 * If the requeue [7] above changed the top waiter,
701 * then we need to wake the new top waiter up to try
702 * to get the lock.
703 */
704 if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
705 wake_up_process(rt_mutex_top_waiter(lock)->task);
706 raw_spin_unlock_irq(&lock->wait_lock);
707 return 0;
708 }
709
710 /* [10] Grab the next task, i.e. the owner of @lock */
711 task = rt_mutex_owner(lock);
712 get_task_struct(task);
713 raw_spin_lock(&task->pi_lock);
714
715 /* [11] requeue the pi waiters if necessary */
716 if (waiter == rt_mutex_top_waiter(lock)) {
717 /*
718 * The waiter became the new top (highest priority)
719 * waiter on the lock. Replace the previous top waiter
720 * in the owner tasks pi waiters tree with this waiter
721 * and adjust the priority of the owner.
722 */
723 rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
724 rt_mutex_enqueue_pi(task, waiter);
725 rt_mutex_adjust_prio(task);
726
727 } else if (prerequeue_top_waiter == waiter) {
728 /*
729 * The waiter was the top waiter on the lock, but is
730 * no longer the top prority waiter. Replace waiter in
731 * the owner tasks pi waiters tree with the new top
732 * (highest priority) waiter and adjust the priority
733 * of the owner.
734 * The new top waiter is stored in @waiter so that
735 * @waiter == @top_waiter evaluates to true below and
736 * we continue to deboost the rest of the chain.
737 */
738 rt_mutex_dequeue_pi(task, waiter);
739 waiter = rt_mutex_top_waiter(lock);
740 rt_mutex_enqueue_pi(task, waiter);
741 rt_mutex_adjust_prio(task);
742 } else {
743 /*
744 * Nothing changed. No need to do any priority
745 * adjustment.
746 */
747 }
748
749 /*
750 * [12] check_exit_conditions_4() protected by task->pi_lock
751 * and lock->wait_lock. The actual decisions are made after we
752 * dropped the locks.
753 *
754 * Check whether the task which owns the current lock is pi
755 * blocked itself. If yes we store a pointer to the lock for
756 * the lock chain change detection above. After we dropped
757 * task->pi_lock next_lock cannot be dereferenced anymore.
758 */
759 next_lock = task_blocked_on_lock(task);
760 /*
761 * Store the top waiter of @lock for the end of chain walk
762 * decision below.
763 */
764 top_waiter = rt_mutex_top_waiter(lock);
765
766 /* [13] Drop the locks */
767 raw_spin_unlock(&task->pi_lock);
768 raw_spin_unlock_irq(&lock->wait_lock);
769
770 /*
771 * Make the actual exit decisions [12], based on the stored
772 * values.
773 *
774 * We reached the end of the lock chain. Stop right here. No
775 * point to go back just to figure that out.
776 */
777 if (!next_lock)
778 goto out_put_task;
779
780 /*
781 * If the current waiter is not the top waiter on the lock,
782 * then we can stop the chain walk here if we are not in full
783 * deadlock detection mode.
784 */
785 if (!detect_deadlock && waiter != top_waiter)
786 goto out_put_task;
787
788 goto again;
789
790 out_unlock_pi:
791 raw_spin_unlock_irq(&task->pi_lock);
792 out_put_task:
793 put_task_struct(task);
794
795 return ret;
796}
797
798/*
799 * Try to take an rt-mutex
800 *
801 * Must be called with lock->wait_lock held and interrupts disabled
802 *
803 * @lock: The lock to be acquired.
804 * @task: The task which wants to acquire the lock
805 * @waiter: The waiter that is queued to the lock's wait tree if the
806 * callsite called task_blocked_on_lock(), otherwise NULL
807 */
808static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
809 struct rt_mutex_waiter *waiter)
810{
811 lockdep_assert_held(&lock->wait_lock);
812
813 /*
814 * Before testing whether we can acquire @lock, we set the
815 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
816 * other tasks which try to modify @lock into the slow path
817 * and they serialize on @lock->wait_lock.
818 *
819 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
820 * as explained at the top of this file if and only if:
821 *
822 * - There is a lock owner. The caller must fixup the
823 * transient state if it does a trylock or leaves the lock
824 * function due to a signal or timeout.
825 *
826 * - @task acquires the lock and there are no other
827 * waiters. This is undone in rt_mutex_set_owner(@task) at
828 * the end of this function.
829 */
830 mark_rt_mutex_waiters(lock);
831
832 /*
833 * If @lock has an owner, give up.
834 */
835 if (rt_mutex_owner(lock))
836 return 0;
837
838 /*
839 * If @waiter != NULL, @task has already enqueued the waiter
840 * into @lock waiter tree. If @waiter == NULL then this is a
841 * trylock attempt.
842 */
843 if (waiter) {
844 /*
845 * If waiter is not the highest priority waiter of
846 * @lock, give up.
847 */
848 if (waiter != rt_mutex_top_waiter(lock))
849 return 0;
850
851 /*
852 * We can acquire the lock. Remove the waiter from the
853 * lock waiters tree.
854 */
855 rt_mutex_dequeue(lock, waiter);
856
857 } else {
858 /*
859 * If the lock has waiters already we check whether @task is
860 * eligible to take over the lock.
861 *
862 * If there are no other waiters, @task can acquire
863 * the lock. @task->pi_blocked_on is NULL, so it does
864 * not need to be dequeued.
865 */
866 if (rt_mutex_has_waiters(lock)) {
867 /*
868 * If @task->prio is greater than or equal to
869 * the top waiter priority (kernel view),
870 * @task lost.
871 */
872 if (!rt_mutex_waiter_less(task_to_waiter(task),
873 rt_mutex_top_waiter(lock)))
874 return 0;
875
876 /*
877 * The current top waiter stays enqueued. We
878 * don't have to change anything in the lock
879 * waiters order.
880 */
881 } else {
882 /*
883 * No waiters. Take the lock without the
884 * pi_lock dance.@task->pi_blocked_on is NULL
885 * and we have no waiters to enqueue in @task
886 * pi waiters tree.
887 */
888 goto takeit;
889 }
890 }
891
892 /*
893 * Clear @task->pi_blocked_on. Requires protection by
894 * @task->pi_lock. Redundant operation for the @waiter == NULL
895 * case, but conditionals are more expensive than a redundant
896 * store.
897 */
898 raw_spin_lock(&task->pi_lock);
899 task->pi_blocked_on = NULL;
900 /*
901 * Finish the lock acquisition. @task is the new owner. If
902 * other waiters exist we have to insert the highest priority
903 * waiter into @task->pi_waiters tree.
904 */
905 if (rt_mutex_has_waiters(lock))
906 rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
907 raw_spin_unlock(&task->pi_lock);
908
909takeit:
910 /* We got the lock. */
911 debug_rt_mutex_lock(lock);
912
913 /*
914 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
915 * are still waiters or clears it.
916 */
917 rt_mutex_set_owner(lock, task);
918
919 return 1;
920}
921
922/*
923 * Task blocks on lock.
924 *
925 * Prepare waiter and propagate pi chain
926 *
927 * This must be called with lock->wait_lock held and interrupts disabled
928 */
929static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
930 struct rt_mutex_waiter *waiter,
931 struct task_struct *task,
932 enum rtmutex_chainwalk chwalk)
933{
934 struct task_struct *owner = rt_mutex_owner(lock);
935 struct rt_mutex_waiter *top_waiter = waiter;
936 struct rt_mutex *next_lock;
937 int chain_walk = 0, res;
938
939 lockdep_assert_held(&lock->wait_lock);
940
941 /*
942 * Early deadlock detection. We really don't want the task to
943 * enqueue on itself just to untangle the mess later. It's not
944 * only an optimization. We drop the locks, so another waiter
945 * can come in before the chain walk detects the deadlock. So
946 * the other will detect the deadlock and return -EDEADLOCK,
947 * which is wrong, as the other waiter is not in a deadlock
948 * situation.
949 */
950 if (owner == task)
951 return -EDEADLK;
952
953 raw_spin_lock(&task->pi_lock);
954 waiter->task = task;
955 waiter->lock = lock;
956 waiter->prio = task->prio;
957 waiter->deadline = task->dl.deadline;
958
959 /* Get the top priority waiter on the lock */
960 if (rt_mutex_has_waiters(lock))
961 top_waiter = rt_mutex_top_waiter(lock);
962 rt_mutex_enqueue(lock, waiter);
963
964 task->pi_blocked_on = waiter;
965
966 raw_spin_unlock(&task->pi_lock);
967
968 if (!owner)
969 return 0;
970
971 raw_spin_lock(&owner->pi_lock);
972 if (waiter == rt_mutex_top_waiter(lock)) {
973 rt_mutex_dequeue_pi(owner, top_waiter);
974 rt_mutex_enqueue_pi(owner, waiter);
975
976 rt_mutex_adjust_prio(owner);
977 if (owner->pi_blocked_on)
978 chain_walk = 1;
979 } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
980 chain_walk = 1;
981 }
982
983 /* Store the lock on which owner is blocked or NULL */
984 next_lock = task_blocked_on_lock(owner);
985
986 raw_spin_unlock(&owner->pi_lock);
987 /*
988 * Even if full deadlock detection is on, if the owner is not
989 * blocked itself, we can avoid finding this out in the chain
990 * walk.
991 */
992 if (!chain_walk || !next_lock)
993 return 0;
994
995 /*
996 * The owner can't disappear while holding a lock,
997 * so the owner struct is protected by wait_lock.
998 * Gets dropped in rt_mutex_adjust_prio_chain()!
999 */
1000 get_task_struct(owner);
1001
1002 raw_spin_unlock_irq(&lock->wait_lock);
1003
1004 res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1005 next_lock, waiter, task);
1006
1007 raw_spin_lock_irq(&lock->wait_lock);
1008
1009 return res;
1010}
1011
1012/*
1013 * Remove the top waiter from the current tasks pi waiter tree and
1014 * queue it up.
1015 *
1016 * Called with lock->wait_lock held and interrupts disabled.
1017 */
1018static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
1019 struct rt_mutex *lock)
1020{
1021 struct rt_mutex_waiter *waiter;
1022
1023 raw_spin_lock(&current->pi_lock);
1024
1025 waiter = rt_mutex_top_waiter(lock);
1026
1027 /*
1028 * Remove it from current->pi_waiters and deboost.
1029 *
1030 * We must in fact deboost here in order to ensure we call
1031 * rt_mutex_setprio() to update p->pi_top_task before the
1032 * task unblocks.
1033 */
1034 rt_mutex_dequeue_pi(current, waiter);
1035 rt_mutex_adjust_prio(current);
1036
1037 /*
1038 * As we are waking up the top waiter, and the waiter stays
1039 * queued on the lock until it gets the lock, this lock
1040 * obviously has waiters. Just set the bit here and this has
1041 * the added benefit of forcing all new tasks into the
1042 * slow path making sure no task of lower priority than
1043 * the top waiter can steal this lock.
1044 */
1045 lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1046
1047 /*
1048 * We deboosted before waking the top waiter task such that we don't
1049 * run two tasks with the 'same' priority (and ensure the
1050 * p->pi_top_task pointer points to a blocked task). This however can
1051 * lead to priority inversion if we would get preempted after the
1052 * deboost but before waking our donor task, hence the preempt_disable()
1053 * before unlock.
1054 *
1055 * Pairs with preempt_enable() in rt_mutex_postunlock();
1056 */
1057 preempt_disable();
1058 wake_q_add(wake_q, waiter->task);
1059 raw_spin_unlock(&current->pi_lock);
1060}
1061
1062/*
1063 * Remove a waiter from a lock and give up
1064 *
1065 * Must be called with lock->wait_lock held and interrupts disabled. I must
1066 * have just failed to try_to_take_rt_mutex().
1067 */
1068static void remove_waiter(struct rt_mutex *lock,
1069 struct rt_mutex_waiter *waiter)
1070{
1071 bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1072 struct task_struct *owner = rt_mutex_owner(lock);
1073 struct rt_mutex *next_lock;
1074
1075 lockdep_assert_held(&lock->wait_lock);
1076
1077 raw_spin_lock(&current->pi_lock);
1078 rt_mutex_dequeue(lock, waiter);
1079 current->pi_blocked_on = NULL;
1080 raw_spin_unlock(&current->pi_lock);
1081
1082 /*
1083 * Only update priority if the waiter was the highest priority
1084 * waiter of the lock and there is an owner to update.
1085 */
1086 if (!owner || !is_top_waiter)
1087 return;
1088
1089 raw_spin_lock(&owner->pi_lock);
1090
1091 rt_mutex_dequeue_pi(owner, waiter);
1092
1093 if (rt_mutex_has_waiters(lock))
1094 rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1095
1096 rt_mutex_adjust_prio(owner);
1097
1098 /* Store the lock on which owner is blocked or NULL */
1099 next_lock = task_blocked_on_lock(owner);
1100
1101 raw_spin_unlock(&owner->pi_lock);
1102
1103 /*
1104 * Don't walk the chain, if the owner task is not blocked
1105 * itself.
1106 */
1107 if (!next_lock)
1108 return;
1109
1110 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1111 get_task_struct(owner);
1112
1113 raw_spin_unlock_irq(&lock->wait_lock);
1114
1115 rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1116 next_lock, NULL, current);
1117
1118 raw_spin_lock_irq(&lock->wait_lock);
1119}
1120
1121/*
1122 * Recheck the pi chain, in case we got a priority setting
1123 *
1124 * Called from sched_setscheduler
1125 */
1126void rt_mutex_adjust_pi(struct task_struct *task)
1127{
1128 struct rt_mutex_waiter *waiter;
1129 struct rt_mutex *next_lock;
1130 unsigned long flags;
1131
1132 raw_spin_lock_irqsave(&task->pi_lock, flags);
1133
1134 waiter = task->pi_blocked_on;
1135 if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
1136 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1137 return;
1138 }
1139 next_lock = waiter->lock;
1140 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1141
1142 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1143 get_task_struct(task);
1144
1145 rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1146 next_lock, NULL, task);
1147}
1148
1149void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
1150{
1151 debug_rt_mutex_init_waiter(waiter);
1152 RB_CLEAR_NODE(&waiter->pi_tree_entry);
1153 RB_CLEAR_NODE(&waiter->tree_entry);
1154 waiter->task = NULL;
1155}
1156
1157/**
1158 * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
1159 * @lock: the rt_mutex to take
1160 * @state: the state the task should block in (TASK_INTERRUPTIBLE
1161 * or TASK_UNINTERRUPTIBLE)
1162 * @timeout: the pre-initialized and started timer, or NULL for none
1163 * @waiter: the pre-initialized rt_mutex_waiter
1164 *
1165 * Must be called with lock->wait_lock held and interrupts disabled
1166 */
1167static int __sched
1168__rt_mutex_slowlock(struct rt_mutex *lock, int state,
1169 struct hrtimer_sleeper *timeout,
1170 struct rt_mutex_waiter *waiter)
1171{
1172 int ret = 0;
1173
1174 for (;;) {
1175 /* Try to acquire the lock: */
1176 if (try_to_take_rt_mutex(lock, current, waiter))
1177 break;
1178
1179 /*
1180 * TASK_INTERRUPTIBLE checks for signals and
1181 * timeout. Ignored otherwise.
1182 */
1183 if (likely(state == TASK_INTERRUPTIBLE)) {
1184 /* Signal pending? */
1185 if (signal_pending(current))
1186 ret = -EINTR;
1187 if (timeout && !timeout->task)
1188 ret = -ETIMEDOUT;
1189 if (ret)
1190 break;
1191 }
1192
1193 raw_spin_unlock_irq(&lock->wait_lock);
1194
1195 debug_rt_mutex_print_deadlock(waiter);
1196
1197 schedule();
1198
1199 raw_spin_lock_irq(&lock->wait_lock);
1200 set_current_state(state);
1201 }
1202
1203 __set_current_state(TASK_RUNNING);
1204 return ret;
1205}
1206
1207static void rt_mutex_handle_deadlock(int res, int detect_deadlock,
1208 struct rt_mutex_waiter *w)
1209{
1210 /*
1211 * If the result is not -EDEADLOCK or the caller requested
1212 * deadlock detection, nothing to do here.
1213 */
1214 if (res != -EDEADLOCK || detect_deadlock)
1215 return;
1216
1217 /*
1218 * Yell lowdly and stop the task right here.
1219 */
1220 rt_mutex_print_deadlock(w);
1221 while (1) {
1222 set_current_state(TASK_INTERRUPTIBLE);
1223 schedule();
1224 }
1225}
1226
1227/*
1228 * Slow path lock function:
1229 */
1230static int __sched
1231rt_mutex_slowlock(struct rt_mutex *lock, int state,
1232 struct hrtimer_sleeper *timeout,
1233 enum rtmutex_chainwalk chwalk)
1234{
1235 struct rt_mutex_waiter waiter;
1236 unsigned long flags;
1237 int ret = 0;
1238
1239 rt_mutex_init_waiter(&waiter);
1240
1241 /*
1242 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1243 * be called in early boot if the cmpxchg() fast path is disabled
1244 * (debug, no architecture support). In this case we will acquire the
1245 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1246 * enable interrupts in that early boot case. So we need to use the
1247 * irqsave/restore variants.
1248 */
1249 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1250
1251 /* Try to acquire the lock again: */
1252 if (try_to_take_rt_mutex(lock, current, NULL)) {
1253 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1254 return 0;
1255 }
1256
1257 set_current_state(state);
1258
1259 /* Setup the timer, when timeout != NULL */
1260 if (unlikely(timeout))
1261 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1262
1263 ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1264
1265 if (likely(!ret))
1266 /* sleep on the mutex */
1267 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1268
1269 if (unlikely(ret)) {
1270 __set_current_state(TASK_RUNNING);
1271 remove_waiter(lock, &waiter);
1272 rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1273 }
1274
1275 /*
1276 * try_to_take_rt_mutex() sets the waiter bit
1277 * unconditionally. We might have to fix that up.
1278 */
1279 fixup_rt_mutex_waiters(lock);
1280
1281 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1282
1283 /* Remove pending timer: */
1284 if (unlikely(timeout))
1285 hrtimer_cancel(&timeout->timer);
1286
1287 debug_rt_mutex_free_waiter(&waiter);
1288
1289 return ret;
1290}
1291
1292static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
1293{
1294 int ret = try_to_take_rt_mutex(lock, current, NULL);
1295
1296 /*
1297 * try_to_take_rt_mutex() sets the lock waiters bit
1298 * unconditionally. Clean this up.
1299 */
1300 fixup_rt_mutex_waiters(lock);
1301
1302 return ret;
1303}
1304
1305/*
1306 * Slow path try-lock function:
1307 */
1308static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1309{
1310 unsigned long flags;
1311 int ret;
1312
1313 /*
1314 * If the lock already has an owner we fail to get the lock.
1315 * This can be done without taking the @lock->wait_lock as
1316 * it is only being read, and this is a trylock anyway.
1317 */
1318 if (rt_mutex_owner(lock))
1319 return 0;
1320
1321 /*
1322 * The mutex has currently no owner. Lock the wait lock and try to
1323 * acquire the lock. We use irqsave here to support early boot calls.
1324 */
1325 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1326
1327 ret = __rt_mutex_slowtrylock(lock);
1328
1329 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1330
1331 return ret;
1332}
1333
1334/*
1335 * Slow path to release a rt-mutex.
1336 *
1337 * Return whether the current task needs to call rt_mutex_postunlock().
1338 */
1339static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1340 struct wake_q_head *wake_q)
1341{
1342 unsigned long flags;
1343
1344 /* irqsave required to support early boot calls */
1345 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1346
1347 debug_rt_mutex_unlock(lock);
1348
1349 /*
1350 * We must be careful here if the fast path is enabled. If we
1351 * have no waiters queued we cannot set owner to NULL here
1352 * because of:
1353 *
1354 * foo->lock->owner = NULL;
1355 * rtmutex_lock(foo->lock); <- fast path
1356 * free = atomic_dec_and_test(foo->refcnt);
1357 * rtmutex_unlock(foo->lock); <- fast path
1358 * if (free)
1359 * kfree(foo);
1360 * raw_spin_unlock(foo->lock->wait_lock);
1361 *
1362 * So for the fastpath enabled kernel:
1363 *
1364 * Nothing can set the waiters bit as long as we hold
1365 * lock->wait_lock. So we do the following sequence:
1366 *
1367 * owner = rt_mutex_owner(lock);
1368 * clear_rt_mutex_waiters(lock);
1369 * raw_spin_unlock(&lock->wait_lock);
1370 * if (cmpxchg(&lock->owner, owner, 0) == owner)
1371 * return;
1372 * goto retry;
1373 *
1374 * The fastpath disabled variant is simple as all access to
1375 * lock->owner is serialized by lock->wait_lock:
1376 *
1377 * lock->owner = NULL;
1378 * raw_spin_unlock(&lock->wait_lock);
1379 */
1380 while (!rt_mutex_has_waiters(lock)) {
1381 /* Drops lock->wait_lock ! */
1382 if (unlock_rt_mutex_safe(lock, flags) == true)
1383 return false;
1384 /* Relock the rtmutex and try again */
1385 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1386 }
1387
1388 /*
1389 * The wakeup next waiter path does not suffer from the above
1390 * race. See the comments there.
1391 *
1392 * Queue the next waiter for wakeup once we release the wait_lock.
1393 */
1394 mark_wakeup_next_waiter(wake_q, lock);
1395 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1396
1397 return true; /* call rt_mutex_postunlock() */
1398}
1399
1400/*
1401 * debug aware fast / slowpath lock,trylock,unlock
1402 *
1403 * The atomic acquire/release ops are compiled away, when either the
1404 * architecture does not support cmpxchg or when debugging is enabled.
1405 */
1406static inline int
1407rt_mutex_fastlock(struct rt_mutex *lock, int state,
1408 int (*slowfn)(struct rt_mutex *lock, int state,
1409 struct hrtimer_sleeper *timeout,
1410 enum rtmutex_chainwalk chwalk))
1411{
1412 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1413 return 0;
1414
1415 return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1416}
1417
1418static inline int
1419rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
1420 struct hrtimer_sleeper *timeout,
1421 enum rtmutex_chainwalk chwalk,
1422 int (*slowfn)(struct rt_mutex *lock, int state,
1423 struct hrtimer_sleeper *timeout,
1424 enum rtmutex_chainwalk chwalk))
1425{
1426 if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1427 likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1428 return 0;
1429
1430 return slowfn(lock, state, timeout, chwalk);
1431}
1432
1433static inline int
1434rt_mutex_fasttrylock(struct rt_mutex *lock,
1435 int (*slowfn)(struct rt_mutex *lock))
1436{
1437 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1438 return 1;
1439
1440 return slowfn(lock);
1441}
1442
1443/*
1444 * Performs the wakeup of the the top-waiter and re-enables preemption.
1445 */
1446void rt_mutex_postunlock(struct wake_q_head *wake_q)
1447{
1448 wake_up_q(wake_q);
1449
1450 /* Pairs with preempt_disable() in rt_mutex_slowunlock() */
1451 preempt_enable();
1452}
1453
1454static inline void
1455rt_mutex_fastunlock(struct rt_mutex *lock,
1456 bool (*slowfn)(struct rt_mutex *lock,
1457 struct wake_q_head *wqh))
1458{
1459 DEFINE_WAKE_Q(wake_q);
1460
1461 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1462 return;
1463
1464 if (slowfn(lock, &wake_q))
1465 rt_mutex_postunlock(&wake_q);
1466}
1467
1468static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
1469{
1470 might_sleep();
1471
1472 mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
1473 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1474}
1475
1476#ifdef CONFIG_DEBUG_LOCK_ALLOC
1477/**
1478 * rt_mutex_lock_nested - lock a rt_mutex
1479 *
1480 * @lock: the rt_mutex to be locked
1481 * @subclass: the lockdep subclass
1482 */
1483void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
1484{
1485 __rt_mutex_lock(lock, subclass);
1486}
1487EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
1488#endif
1489
1490#ifndef CONFIG_DEBUG_LOCK_ALLOC
1491/**
1492 * rt_mutex_lock - lock a rt_mutex
1493 *
1494 * @lock: the rt_mutex to be locked
1495 */
1496void __sched rt_mutex_lock(struct rt_mutex *lock)
1497{
1498 __rt_mutex_lock(lock, 0);
1499}
1500EXPORT_SYMBOL_GPL(rt_mutex_lock);
1501#endif
1502
1503/**
1504 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1505 *
1506 * @lock: the rt_mutex to be locked
1507 *
1508 * Returns:
1509 * 0 on success
1510 * -EINTR when interrupted by a signal
1511 */
1512int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1513{
1514 int ret;
1515
1516 might_sleep();
1517
1518 mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1519 ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1520 if (ret)
1521 mutex_release(&lock->dep_map, 1, _RET_IP_);
1522
1523 return ret;
1524}
1525EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1526
1527/*
1528 * Futex variant, must not use fastpath.
1529 */
1530int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
1531{
1532 return rt_mutex_slowtrylock(lock);
1533}
1534
1535int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
1536{
1537 return __rt_mutex_slowtrylock(lock);
1538}
1539
1540/**
1541 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1542 * the timeout structure is provided
1543 * by the caller
1544 *
1545 * @lock: the rt_mutex to be locked
1546 * @timeout: timeout structure or NULL (no timeout)
1547 *
1548 * Returns:
1549 * 0 on success
1550 * -EINTR when interrupted by a signal
1551 * -ETIMEDOUT when the timeout expired
1552 */
1553int
1554rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1555{
1556 int ret;
1557
1558 might_sleep();
1559
1560 mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1561 ret = rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1562 RT_MUTEX_MIN_CHAINWALK,
1563 rt_mutex_slowlock);
1564 if (ret)
1565 mutex_release(&lock->dep_map, 1, _RET_IP_);
1566
1567 return ret;
1568}
1569EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1570
1571/**
1572 * rt_mutex_trylock - try to lock a rt_mutex
1573 *
1574 * @lock: the rt_mutex to be locked
1575 *
1576 * This function can only be called in thread context. It's safe to
1577 * call it from atomic regions, but not from hard interrupt or soft
1578 * interrupt context.
1579 *
1580 * Returns 1 on success and 0 on contention
1581 */
1582int __sched rt_mutex_trylock(struct rt_mutex *lock)
1583{
1584 int ret;
1585
1586 if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
1587 return 0;
1588
1589 ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1590 if (ret)
1591 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1592
1593 return ret;
1594}
1595EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1596
1597/**
1598 * rt_mutex_unlock - unlock a rt_mutex
1599 *
1600 * @lock: the rt_mutex to be unlocked
1601 */
1602void __sched rt_mutex_unlock(struct rt_mutex *lock)
1603{
1604 mutex_release(&lock->dep_map, 1, _RET_IP_);
1605 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1606}
1607EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1608
1609/**
1610 * Futex variant, that since futex variants do not use the fast-path, can be
1611 * simple and will not need to retry.
1612 */
1613bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
1614 struct wake_q_head *wake_q)
1615{
1616 lockdep_assert_held(&lock->wait_lock);
1617
1618 debug_rt_mutex_unlock(lock);
1619
1620 if (!rt_mutex_has_waiters(lock)) {
1621 lock->owner = NULL;
1622 return false; /* done */
1623 }
1624
1625 /*
1626 * We've already deboosted, mark_wakeup_next_waiter() will
1627 * retain preempt_disabled when we drop the wait_lock, to
1628 * avoid inversion prior to the wakeup. preempt_disable()
1629 * therein pairs with rt_mutex_postunlock().
1630 */
1631 mark_wakeup_next_waiter(wake_q, lock);
1632
1633 return true; /* call postunlock() */
1634}
1635
1636void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
1637{
1638 DEFINE_WAKE_Q(wake_q);
1639 unsigned long flags;
1640 bool postunlock;
1641
1642 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1643 postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
1644 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1645
1646 if (postunlock)
1647 rt_mutex_postunlock(&wake_q);
1648}
1649
1650/**
1651 * rt_mutex_destroy - mark a mutex unusable
1652 * @lock: the mutex to be destroyed
1653 *
1654 * This function marks the mutex uninitialized, and any subsequent
1655 * use of the mutex is forbidden. The mutex must not be locked when
1656 * this function is called.
1657 */
1658void rt_mutex_destroy(struct rt_mutex *lock)
1659{
1660 WARN_ON(rt_mutex_is_locked(lock));
1661#ifdef CONFIG_DEBUG_RT_MUTEXES
1662 lock->magic = NULL;
1663#endif
1664}
1665EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1666
1667/**
1668 * __rt_mutex_init - initialize the rt lock
1669 *
1670 * @lock: the rt lock to be initialized
1671 *
1672 * Initialize the rt lock to unlocked state.
1673 *
1674 * Initializing of a locked rt lock is not allowed
1675 */
1676void __rt_mutex_init(struct rt_mutex *lock, const char *name,
1677 struct lock_class_key *key)
1678{
1679 lock->owner = NULL;
1680 raw_spin_lock_init(&lock->wait_lock);
1681 lock->waiters = RB_ROOT_CACHED;
1682
1683 if (name && key)
1684 debug_rt_mutex_init(lock, name, key);
1685}
1686EXPORT_SYMBOL_GPL(__rt_mutex_init);
1687
1688/**
1689 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1690 * proxy owner
1691 *
1692 * @lock: the rt_mutex to be locked
1693 * @proxy_owner:the task to set as owner
1694 *
1695 * No locking. Caller has to do serializing itself
1696 *
1697 * Special API call for PI-futex support. This initializes the rtmutex and
1698 * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
1699 * possible at this point because the pi_state which contains the rtmutex
1700 * is not yet visible to other tasks.
1701 */
1702void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1703 struct task_struct *proxy_owner)
1704{
1705 __rt_mutex_init(lock, NULL, NULL);
1706 debug_rt_mutex_proxy_lock(lock, proxy_owner);
1707 rt_mutex_set_owner(lock, proxy_owner);
1708}
1709
1710/**
1711 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1712 *
1713 * @lock: the rt_mutex to be locked
1714 *
1715 * No locking. Caller has to do serializing itself
1716 *
1717 * Special API call for PI-futex support. This merrily cleans up the rtmutex
1718 * (debugging) state. Concurrent operations on this rt_mutex are not
1719 * possible because it belongs to the pi_state which is about to be freed
1720 * and it is not longer visible to other tasks.
1721 */
1722void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1723 struct task_struct *proxy_owner)
1724{
1725 debug_rt_mutex_proxy_unlock(lock);
1726 rt_mutex_set_owner(lock, NULL);
1727}
1728
1729int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1730 struct rt_mutex_waiter *waiter,
1731 struct task_struct *task)
1732{
1733 int ret;
1734
1735 if (try_to_take_rt_mutex(lock, task, NULL))
1736 return 1;
1737
1738 /* We enforce deadlock detection for futexes */
1739 ret = task_blocks_on_rt_mutex(lock, waiter, task,
1740 RT_MUTEX_FULL_CHAINWALK);
1741
1742 if (ret && !rt_mutex_owner(lock)) {
1743 /*
1744 * Reset the return value. We might have
1745 * returned with -EDEADLK and the owner
1746 * released the lock while we were walking the
1747 * pi chain. Let the waiter sort it out.
1748 */
1749 ret = 0;
1750 }
1751
1752 if (unlikely(ret))
1753 remove_waiter(lock, waiter);
1754
1755 debug_rt_mutex_print_deadlock(waiter);
1756
1757 return ret;
1758}
1759
1760/**
1761 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1762 * @lock: the rt_mutex to take
1763 * @waiter: the pre-initialized rt_mutex_waiter
1764 * @task: the task to prepare
1765 *
1766 * Returns:
1767 * 0 - task blocked on lock
1768 * 1 - acquired the lock for task, caller should wake it up
1769 * <0 - error
1770 *
1771 * Special API call for FUTEX_REQUEUE_PI support.
1772 */
1773int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1774 struct rt_mutex_waiter *waiter,
1775 struct task_struct *task)
1776{
1777 int ret;
1778
1779 raw_spin_lock_irq(&lock->wait_lock);
1780 ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
1781 raw_spin_unlock_irq(&lock->wait_lock);
1782
1783 return ret;
1784}
1785
1786/**
1787 * rt_mutex_next_owner - return the next owner of the lock
1788 *
1789 * @lock: the rt lock query
1790 *
1791 * Returns the next owner of the lock or NULL
1792 *
1793 * Caller has to serialize against other accessors to the lock
1794 * itself.
1795 *
1796 * Special API call for PI-futex support
1797 */
1798struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1799{
1800 if (!rt_mutex_has_waiters(lock))
1801 return NULL;
1802
1803 return rt_mutex_top_waiter(lock)->task;
1804}
1805
1806/**
1807 * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
1808 * @lock: the rt_mutex we were woken on
1809 * @to: the timeout, null if none. hrtimer should already have
1810 * been started.
1811 * @waiter: the pre-initialized rt_mutex_waiter
1812 *
1813 * Wait for the the lock acquisition started on our behalf by
1814 * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
1815 * rt_mutex_cleanup_proxy_lock().
1816 *
1817 * Returns:
1818 * 0 - success
1819 * <0 - error, one of -EINTR, -ETIMEDOUT
1820 *
1821 * Special API call for PI-futex support
1822 */
1823int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
1824 struct hrtimer_sleeper *to,
1825 struct rt_mutex_waiter *waiter)
1826{
1827 int ret;
1828
1829 raw_spin_lock_irq(&lock->wait_lock);
1830 /* sleep on the mutex */
1831 set_current_state(TASK_INTERRUPTIBLE);
1832 ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1833 /*
1834 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1835 * have to fix that up.
1836 */
1837 fixup_rt_mutex_waiters(lock);
1838 raw_spin_unlock_irq(&lock->wait_lock);
1839
1840 return ret;
1841}
1842
1843/**
1844 * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
1845 * @lock: the rt_mutex we were woken on
1846 * @waiter: the pre-initialized rt_mutex_waiter
1847 *
1848 * Attempt to clean up after a failed rt_mutex_wait_proxy_lock().
1849 *
1850 * Unless we acquired the lock; we're still enqueued on the wait-list and can
1851 * in fact still be granted ownership until we're removed. Therefore we can
1852 * find we are in fact the owner and must disregard the
1853 * rt_mutex_wait_proxy_lock() failure.
1854 *
1855 * Returns:
1856 * true - did the cleanup, we done.
1857 * false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
1858 * caller should disregards its return value.
1859 *
1860 * Special API call for PI-futex support
1861 */
1862bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
1863 struct rt_mutex_waiter *waiter)
1864{
1865 bool cleanup = false;
1866
1867 raw_spin_lock_irq(&lock->wait_lock);
1868 /*
1869 * Do an unconditional try-lock, this deals with the lock stealing
1870 * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
1871 * sets a NULL owner.
1872 *
1873 * We're not interested in the return value, because the subsequent
1874 * test on rt_mutex_owner() will infer that. If the trylock succeeded,
1875 * we will own the lock and it will have removed the waiter. If we
1876 * failed the trylock, we're still not owner and we need to remove
1877 * ourselves.
1878 */
1879 try_to_take_rt_mutex(lock, current, waiter);
1880 /*
1881 * Unless we're the owner; we're still enqueued on the wait_list.
1882 * So check if we became owner, if not, take us off the wait_list.
1883 */
1884 if (rt_mutex_owner(lock) != current) {
1885 remove_waiter(lock, waiter);
1886 cleanup = true;
1887 }
1888 /*
1889 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1890 * have to fix that up.
1891 */
1892 fixup_rt_mutex_waiters(lock);
1893
1894 raw_spin_unlock_irq(&lock->wait_lock);
1895
1896 return cleanup;
1897}