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