1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * RT-Mutexes: simple blocking mutual exclusion locks with PI support
4 *
5 * started by Ingo Molnar and Thomas Gleixner.
6 *
7 * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8 * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
9 * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
10 * Copyright (C) 2006 Esben Nielsen
11 *
12 * See Documentation/locking/rt-mutex-design.rst for details.
13 */
14 #include <linux/spinlock.h>
15 #include <linux/export.h>
16 #include <linux/sched/signal.h>
17 #include <linux/sched/rt.h>
18 #include <linux/sched/deadline.h>
19 #include <linux/sched/wake_q.h>
20 #include <linux/sched/debug.h>
21 #include <linux/timer.h>
22
23 #include "rtmutex_common.h"
24
25 /*
26 * lock->owner state tracking:
27 *
28 * lock->owner holds the task_struct pointer of the owner. Bit 0
29 * is used to keep track of the "lock has waiters" state.
30 *
31 * owner bit0
32 * NULL 0 lock is free (fast acquire possible)
33 * NULL 1 lock is free and has waiters and the top waiter
34 * is going to take the lock*
35 * taskpointer 0 lock is held (fast release possible)
36 * taskpointer 1 lock is held and has waiters**
37 *
38 * The fast atomic compare exchange based acquire and release is only
39 * possible when bit 0 of lock->owner is 0.
40 *
41 * (*) It also can be a transitional state when grabbing the lock
42 * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
43 * we need to set the bit0 before looking at the lock, and the owner may be
44 * NULL in this small time, hence this can be a transitional state.
45 *
46 * (**) There is a small time when bit 0 is set but there are no
47 * waiters. This can happen when grabbing the lock in the slow path.
48 * To prevent a cmpxchg of the owner releasing the lock, we need to
49 * set this bit before looking at the lock.
50 */
51
52 static void
53 rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
54 {
55 unsigned long val = (unsigned long)owner;
56
57 if (rt_mutex_has_waiters(lock))
58 val |= RT_MUTEX_HAS_WAITERS;
59
60 lock->owner = (struct task_struct *)val;
61 }
62
63 static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
64 {
65 lock->owner = (struct task_struct *)
66 ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
67 }
68
69 static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
70 {
71 unsigned long owner, *p = (unsigned long *) &lock->owner;
72
73 if (rt_mutex_has_waiters(lock))
74 return;
75
76 /*
77 * The rbtree has no waiters enqueued, now make sure that the
78 * lock->owner still has the waiters bit set, otherwise the
79 * following can happen:
80 *
81 * CPU 0 CPU 1 CPU2
82 * l->owner=T1
83 * rt_mutex_lock(l)
84 * lock(l->lock)
85 * l->owner = T1 | HAS_WAITERS;
86 * enqueue(T2)
87 * boost()
88 * unlock(l->lock)
89 * block()
90 *
91 * rt_mutex_lock(l)
92 * lock(l->lock)
93 * l->owner = T1 | HAS_WAITERS;
94 * enqueue(T3)
95 * boost()
96 * unlock(l->lock)
97 * block()
98 * signal(->T2) signal(->T3)
99 * lock(l->lock)
100 * dequeue(T2)
101 * deboost()
102 * unlock(l->lock)
103 * lock(l->lock)
104 * dequeue(T3)
105 * ==> wait list is empty
106 * deboost()
107 * unlock(l->lock)
108 * lock(l->lock)
109 * fixup_rt_mutex_waiters()
110 * if (wait_list_empty(l) {
111 * l->owner = owner
112 * owner = l->owner & ~HAS_WAITERS;
113 * ==> l->owner = T1
114 * }
115 * lock(l->lock)
116 * rt_mutex_unlock(l) fixup_rt_mutex_waiters()
117 * if (wait_list_empty(l) {
118 * owner = l->owner & ~HAS_WAITERS;
119 * cmpxchg(l->owner, T1, NULL)
120 * ===> Success (l->owner = NULL)
121 *
122 * l->owner = owner
123 * ==> l->owner = T1
124 * }
125 *
126 * With the check for the waiter bit in place T3 on CPU2 will not
127 * overwrite. All tasks fiddling with the waiters bit are
128 * serialized by l->lock, so nothing else can modify the waiters
129 * bit. If the bit is set then nothing can change l->owner either
130 * so the simple RMW is safe. The cmpxchg() will simply fail if it
131 * happens in the middle of the RMW because the waiters bit is
132 * still set.
133 */
134 owner = READ_ONCE(*p);
135 if (owner & RT_MUTEX_HAS_WAITERS)
136 WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
137 }
138
139 /*
140 * We can speed up the acquire/release, if there's no debugging state to be
141 * set up.
142 */
143 #ifndef CONFIG_DEBUG_RT_MUTEXES
144 # define rt_mutex_cmpxchg_relaxed(l,c,n) (cmpxchg_relaxed(&l->owner, c, n) == c)
145 # define rt_mutex_cmpxchg_acquire(l,c,n) (cmpxchg_acquire(&l->owner, c, n) == c)
146 # define rt_mutex_cmpxchg_release(l,c,n) (cmpxchg_release(&l->owner, c, n) == c)
147
148 /*
149 * Callers must hold the ->wait_lock -- which is the whole purpose as we force
150 * all future threads that attempt to [Rmw] the lock to the slowpath. As such
151 * relaxed semantics suffice.
152 */
153 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
154 {
155 unsigned long owner, *p = (unsigned long *) &lock->owner;
156
157 do {
158 owner = *p;
159 } while (cmpxchg_relaxed(p, owner,
160 owner | RT_MUTEX_HAS_WAITERS) != owner);
161 }
162
163 /*
164 * Safe fastpath aware unlock:
165 * 1) Clear the waiters bit
166 * 2) Drop lock->wait_lock
167 * 3) Try to unlock the lock with cmpxchg
168 */
169 static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
170 unsigned long flags)
171 __releases(lock->wait_lock)
172 {
173 struct task_struct *owner = rt_mutex_owner(lock);
174
175 clear_rt_mutex_waiters(lock);
176 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
177 /*
178 * If a new waiter comes in between the unlock and the cmpxchg
179 * we have two situations:
180 *
181 * unlock(wait_lock);
182 * lock(wait_lock);
183 * cmpxchg(p, owner, 0) == owner
184 * mark_rt_mutex_waiters(lock);
185 * acquire(lock);
186 * or:
187 *
188 * unlock(wait_lock);
189 * lock(wait_lock);
190 * mark_rt_mutex_waiters(lock);
191 *
192 * cmpxchg(p, owner, 0) != owner
193 * enqueue_waiter();
194 * unlock(wait_lock);
195 * lock(wait_lock);
196 * wake waiter();
197 * unlock(wait_lock);
198 * lock(wait_lock);
199 * acquire(lock);
200 */
201 return rt_mutex_cmpxchg_release(lock, owner, NULL);
202 }
203
204 #else
205 # define rt_mutex_cmpxchg_relaxed(l,c,n) (0)
206 # define rt_mutex_cmpxchg_acquire(l,c,n) (0)
207 # define rt_mutex_cmpxchg_release(l,c,n) (0)
208
209 static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
210 {
211 lock->owner = (struct task_struct *)
212 ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
213 }
214
215 /*
216 * Simple slow path only version: lock->owner is protected by lock->wait_lock.
217 */
218 static inline bool unlock_rt_mutex_safe(struct rt_mutex *lock,
219 unsigned long flags)
220 __releases(lock->wait_lock)
221 {
222 lock->owner = NULL;
223 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
224 return true;
225 }
226 #endif
227
228 /*
229 * Only use with rt_mutex_waiter_{less,equal}()
230 */
231 #define task_to_waiter(p) \
232 &(struct rt_mutex_waiter){ .prio = (p)->prio, .deadline = (p)->dl.deadline }
233
234 static inline int
235 rt_mutex_waiter_less(struct rt_mutex_waiter *left,
236 struct rt_mutex_waiter *right)
237 {
238 if (left->prio < right->prio)
239 return 1;
240
241 /*
242 * If both waiters have dl_prio(), we check the deadlines of the
243 * associated tasks.
244 * If left waiter has a dl_prio(), and we didn't return 1 above,
245 * then right waiter has a dl_prio() too.
246 */
247 if (dl_prio(left->prio))
248 return dl_time_before(left->deadline, right->deadline);
249
250 return 0;
251 }
252
253 static inline int
254 rt_mutex_waiter_equal(struct rt_mutex_waiter *left,
255 struct rt_mutex_waiter *right)
256 {
257 if (left->prio != right->prio)
258 return 0;
259
260 /*
261 * If both waiters have dl_prio(), we check the deadlines of the
262 * associated tasks.
263 * If left waiter has a dl_prio(), and we didn't return 0 above,
264 * then right waiter has a dl_prio() too.
265 */
266 if (dl_prio(left->prio))
267 return left->deadline == right->deadline;
268
269 return 1;
270 }
271
272 static void
273 rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
274 {
275 struct rb_node **link = &lock->waiters.rb_root.rb_node;
276 struct rb_node *parent = NULL;
277 struct rt_mutex_waiter *entry;
278 bool leftmost = true;
279
280 while (*link) {
281 parent = *link;
282 entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
283 if (rt_mutex_waiter_less(waiter, entry)) {
284 link = &parent->rb_left;
285 } else {
286 link = &parent->rb_right;
287 leftmost = false;
288 }
289 }
290
291 rb_link_node(&waiter->tree_entry, parent, link);
292 rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
293 }
294
295 static void
296 rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
297 {
298 if (RB_EMPTY_NODE(&waiter->tree_entry))
299 return;
300
301 rb_erase_cached(&waiter->tree_entry, &lock->waiters);
302 RB_CLEAR_NODE(&waiter->tree_entry);
303 }
304
305 static void
306 rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
307 {
308 struct rb_node **link = &task->pi_waiters.rb_root.rb_node;
309 struct rb_node *parent = NULL;
310 struct rt_mutex_waiter *entry;
311 bool leftmost = true;
312
313 while (*link) {
314 parent = *link;
315 entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
316 if (rt_mutex_waiter_less(waiter, entry)) {
317 link = &parent->rb_left;
318 } else {
319 link = &parent->rb_right;
320 leftmost = false;
321 }
322 }
323
324 rb_link_node(&waiter->pi_tree_entry, parent, link);
325 rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
326 }
327
328 static void
329 rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
330 {
331 if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
332 return;
333
334 rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
335 RB_CLEAR_NODE(&waiter->pi_tree_entry);
336 }
337
338 static void rt_mutex_adjust_prio(struct task_struct *p)
339 {
340 struct task_struct *pi_task = NULL;
341
342 lockdep_assert_held(&p->pi_lock);
343
344 if (task_has_pi_waiters(p))
345 pi_task = task_top_pi_waiter(p)->task;
346
347 rt_mutex_setprio(p, pi_task);
348 }
349
350 /*
351 * Deadlock detection is conditional:
352 *
353 * If CONFIG_DEBUG_RT_MUTEXES=n, deadlock detection is only conducted
354 * if the detect argument is == RT_MUTEX_FULL_CHAINWALK.
355 *
356 * If CONFIG_DEBUG_RT_MUTEXES=y, deadlock detection is always
357 * conducted independent of the detect argument.
358 *
359 * If the waiter argument is NULL this indicates the deboost path and
360 * deadlock detection is disabled independent of the detect argument
361 * and the config settings.
362 */
363 static bool rt_mutex_cond_detect_deadlock(struct rt_mutex_waiter *waiter,
364 enum rtmutex_chainwalk chwalk)
365 {
366 /*
367 * This is just a wrapper function for the following call,
368 * because debug_rt_mutex_detect_deadlock() smells like a magic
369 * debug feature and I wanted to keep the cond function in the
370 * main source file along with the comments instead of having
371 * two of the same in the headers.
372 */
373 return debug_rt_mutex_detect_deadlock(waiter, chwalk);
374 }
375
376 /*
377 * Max number of times we'll walk the boosting chain:
378 */
379 int max_lock_depth = 1024;
380
381 static inline struct rt_mutex *task_blocked_on_lock(struct task_struct *p)
382 {
383 return p->pi_blocked_on ? p->pi_blocked_on->lock : NULL;
384 }
385
386 /*
387 * Adjust the priority chain. Also used for deadlock detection.
388 * Decreases task's usage by one - may thus free the task.
389 *
390 * @task: the task owning the mutex (owner) for which a chain walk is
391 * probably needed
392 * @chwalk: do we have to carry out deadlock detection?
393 * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
394 * things for a task that has just got its priority adjusted, and
395 * is waiting on a mutex)
396 * @next_lock: the mutex on which the owner of @orig_lock was blocked before
397 * we dropped its pi_lock. Is never dereferenced, only used for
398 * comparison to detect lock chain changes.
399 * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
400 * its priority to the mutex owner (can be NULL in the case
401 * depicted above or if the top waiter is gone away and we are
402 * actually deboosting the owner)
403 * @top_task: the current top waiter
404 *
405 * Returns 0 or -EDEADLK.
406 *
407 * Chain walk basics and protection scope
408 *
409 * [R] refcount on task
410 * [P] task->pi_lock held
411 * [L] rtmutex->wait_lock held
412 *
413 * Step Description Protected by
414 * function arguments:
415 * @task [R]
416 * @orig_lock if != NULL @top_task is blocked on it
417 * @next_lock Unprotected. Cannot be
418 * dereferenced. Only used for
419 * comparison.
420 * @orig_waiter if != NULL @top_task is blocked on it
421 * @top_task current, or in case of proxy
422 * locking protected by calling
423 * code
424 * again:
425 * loop_sanity_check();
426 * retry:
427 * [1] lock(task->pi_lock); [R] acquire [P]
428 * [2] waiter = task->pi_blocked_on; [P]
429 * [3] check_exit_conditions_1(); [P]
430 * [4] lock = waiter->lock; [P]
431 * [5] if (!try_lock(lock->wait_lock)) { [P] try to acquire [L]
432 * unlock(task->pi_lock); release [P]
433 * goto retry;
434 * }
435 * [6] check_exit_conditions_2(); [P] + [L]
436 * [7] requeue_lock_waiter(lock, waiter); [P] + [L]
437 * [8] unlock(task->pi_lock); release [P]
438 * put_task_struct(task); release [R]
439 * [9] check_exit_conditions_3(); [L]
440 * [10] task = owner(lock); [L]
441 * get_task_struct(task); [L] acquire [R]
442 * lock(task->pi_lock); [L] acquire [P]
443 * [11] requeue_pi_waiter(tsk, waiters(lock));[P] + [L]
444 * [12] check_exit_conditions_4(); [P] + [L]
445 * [13] unlock(task->pi_lock); release [P]
446 * unlock(lock->wait_lock); release [L]
447 * goto again;
448 */
449 static int rt_mutex_adjust_prio_chain(struct task_struct *task,
450 enum rtmutex_chainwalk chwalk,
451 struct rt_mutex *orig_lock,
452 struct rt_mutex *next_lock,
453 struct rt_mutex_waiter *orig_waiter,
454 struct task_struct *top_task)
455 {
456 struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
457 struct rt_mutex_waiter *prerequeue_top_waiter;
458 int ret = 0, depth = 0;
459 struct rt_mutex *lock;
460 bool detect_deadlock;
461 bool requeue = true;
462
463 detect_deadlock = rt_mutex_cond_detect_deadlock(orig_waiter, chwalk);
464
465 /*
466 * The (de)boosting is a step by step approach with a lot of
467 * pitfalls. We want this to be preemptible and we want hold a
468 * maximum of two locks per step. So we have to check
469 * carefully whether things change under us.
470 */
471 again:
472 /*
473 * We limit the lock chain length for each invocation.
474 */
475 if (++depth > max_lock_depth) {
476 static int prev_max;
477
478 /*
479 * Print this only once. If the admin changes the limit,
480 * print a new message when reaching the limit again.
481 */
482 if (prev_max != max_lock_depth) {
483 prev_max = max_lock_depth;
484 printk(KERN_WARNING "Maximum lock depth %d reached "
485 "task: %s (%d)\n", max_lock_depth,
486 top_task->comm, task_pid_nr(top_task));
487 }
488 put_task_struct(task);
489
490 return -EDEADLK;
491 }
492
493 /*
494 * We are fully preemptible here and only hold the refcount on
495 * @task. So everything can have changed under us since the
496 * caller or our own code below (goto retry/again) dropped all
497 * locks.
498 */
499 retry:
500 /*
501 * [1] Task cannot go away as we did a get_task() before !
502 */
503 raw_spin_lock_irq(&task->pi_lock);
504
505 /*
506 * [2] Get the waiter on which @task is blocked on.
507 */
508 waiter = task->pi_blocked_on;
509
510 /*
511 * [3] check_exit_conditions_1() protected by task->pi_lock.
512 */
513
514 /*
515 * Check whether the end of the boosting chain has been
516 * reached or the state of the chain has changed while we
517 * dropped the locks.
518 */
519 if (!waiter)
520 goto out_unlock_pi;
521
522 /*
523 * Check the orig_waiter state. After we dropped the locks,
524 * the previous owner of the lock might have released the lock.
525 */
526 if (orig_waiter && !rt_mutex_owner(orig_lock))
527 goto out_unlock_pi;
528
529 /*
530 * We dropped all locks after taking a refcount on @task, so
531 * the task might have moved on in the lock chain or even left
532 * the chain completely and blocks now on an unrelated lock or
533 * on @orig_lock.
534 *
535 * We stored the lock on which @task was blocked in @next_lock,
536 * so we can detect the chain change.
537 */
538 if (next_lock != waiter->lock)
539 goto out_unlock_pi;
540
541 /*
542 * Drop out, when the task has no waiters. Note,
543 * top_waiter can be NULL, when we are in the deboosting
544 * mode!
545 */
546 if (top_waiter) {
547 if (!task_has_pi_waiters(task))
548 goto out_unlock_pi;
549 /*
550 * If deadlock detection is off, we stop here if we
551 * are not the top pi waiter of the task. If deadlock
552 * detection is enabled we continue, but stop the
553 * requeueing in the chain walk.
554 */
555 if (top_waiter != task_top_pi_waiter(task)) {
556 if (!detect_deadlock)
557 goto out_unlock_pi;
558 else
559 requeue = false;
560 }
561 }
562
563 /*
564 * If the waiter priority is the same as the task priority
565 * then there is no further priority adjustment necessary. If
566 * deadlock detection is off, we stop the chain walk. If its
567 * enabled we continue, but stop the requeueing in the chain
568 * walk.
569 */
570 if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
571 if (!detect_deadlock)
572 goto out_unlock_pi;
573 else
574 requeue = false;
575 }
576
577 /*
578 * [4] Get the next lock
579 */
580 lock = waiter->lock;
581 /*
582 * [5] We need to trylock here as we are holding task->pi_lock,
583 * which is the reverse lock order versus the other rtmutex
584 * operations.
585 */
586 if (!raw_spin_trylock(&lock->wait_lock)) {
587 raw_spin_unlock_irq(&task->pi_lock);
588 cpu_relax();
589 goto retry;
590 }
591
592 /*
593 * [6] check_exit_conditions_2() protected by task->pi_lock and
594 * lock->wait_lock.
595 *
596 * Deadlock detection. If the lock is the same as the original
597 * lock which caused us to walk the lock chain or if the
598 * current lock is owned by the task which initiated the chain
599 * walk, we detected a deadlock.
600 */
601 if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
602 debug_rt_mutex_deadlock(chwalk, orig_waiter, lock);
603 raw_spin_unlock(&lock->wait_lock);
604 ret = -EDEADLK;
605 goto out_unlock_pi;
606 }
607
608 /*
609 * If we just follow the lock chain for deadlock detection, no
610 * need to do all the requeue operations. To avoid a truckload
611 * of conditionals around the various places below, just do the
612 * minimum chain walk checks.
613 */
614 if (!requeue) {
615 /*
616 * No requeue[7] here. Just release @task [8]
617 */
618 raw_spin_unlock(&task->pi_lock);
619 put_task_struct(task);
620
621 /*
622 * [9] check_exit_conditions_3 protected by lock->wait_lock.
623 * If there is no owner of the lock, end of chain.
624 */
625 if (!rt_mutex_owner(lock)) {
626 raw_spin_unlock_irq(&lock->wait_lock);
627 return 0;
628 }
629
630 /* [10] Grab the next task, i.e. owner of @lock */
631 task = get_task_struct(rt_mutex_owner(lock));
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 = get_task_struct(rt_mutex_owner(lock));
712 raw_spin_lock(&task->pi_lock);
713
714 /* [11] requeue the pi waiters if necessary */
715 if (waiter == rt_mutex_top_waiter(lock)) {
716 /*
717 * The waiter became the new top (highest priority)
718 * waiter on the lock. Replace the previous top waiter
719 * in the owner tasks pi waiters tree with this waiter
720 * and adjust the priority of the owner.
721 */
722 rt_mutex_dequeue_pi(task, prerequeue_top_waiter);
723 rt_mutex_enqueue_pi(task, waiter);
724 rt_mutex_adjust_prio(task);
725
726 } else if (prerequeue_top_waiter == waiter) {
727 /*
728 * The waiter was the top waiter on the lock, but is
729 * no longer the top prority waiter. Replace waiter in
730 * the owner tasks pi waiters tree with the new top
731 * (highest priority) waiter and adjust the priority
732 * of the owner.
733 * The new top waiter is stored in @waiter so that
734 * @waiter == @top_waiter evaluates to true below and
735 * we continue to deboost the rest of the chain.
736 */
737 rt_mutex_dequeue_pi(task, waiter);
738 waiter = rt_mutex_top_waiter(lock);
739 rt_mutex_enqueue_pi(task, waiter);
740 rt_mutex_adjust_prio(task);
741 } else {
742 /*
743 * Nothing changed. No need to do any priority
744 * adjustment.
745 */
746 }
747
748 /*
749 * [12] check_exit_conditions_4() protected by task->pi_lock
750 * and lock->wait_lock. The actual decisions are made after we
751 * dropped the locks.
752 *
753 * Check whether the task which owns the current lock is pi
754 * blocked itself. If yes we store a pointer to the lock for
755 * the lock chain change detection above. After we dropped
756 * task->pi_lock next_lock cannot be dereferenced anymore.
757 */
758 next_lock = task_blocked_on_lock(task);
759 /*
760 * Store the top waiter of @lock for the end of chain walk
761 * decision below.
762 */
763 top_waiter = rt_mutex_top_waiter(lock);
764
765 /* [13] Drop the locks */
766 raw_spin_unlock(&task->pi_lock);
767 raw_spin_unlock_irq(&lock->wait_lock);
768
769 /*
770 * Make the actual exit decisions [12], based on the stored
771 * values.
772 *
773 * We reached the end of the lock chain. Stop right here. No
774 * point to go back just to figure that out.
775 */
776 if (!next_lock)
777 goto out_put_task;
778
779 /*
780 * If the current waiter is not the top waiter on the lock,
781 * then we can stop the chain walk here if we are not in full
782 * deadlock detection mode.
783 */
784 if (!detect_deadlock && waiter != top_waiter)
785 goto out_put_task;
786
787 goto again;
788
789 out_unlock_pi:
790 raw_spin_unlock_irq(&task->pi_lock);
791 out_put_task:
792 put_task_struct(task);
793
794 return ret;
795 }
796
797 /*
798 * Try to take an rt-mutex
799 *
800 * Must be called with lock->wait_lock held and interrupts disabled
801 *
802 * @lock: The lock to be acquired.
803 * @task: The task which wants to acquire the lock
804 * @waiter: The waiter that is queued to the lock's wait tree if the
805 * callsite called task_blocked_on_lock(), otherwise NULL
806 */
807 static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
808 struct rt_mutex_waiter *waiter)
809 {
810 lockdep_assert_held(&lock->wait_lock);
811
812 /*
813 * Before testing whether we can acquire @lock, we set the
814 * RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
815 * other tasks which try to modify @lock into the slow path
816 * and they serialize on @lock->wait_lock.
817 *
818 * The RT_MUTEX_HAS_WAITERS bit can have a transitional state
819 * as explained at the top of this file if and only if:
820 *
821 * - There is a lock owner. The caller must fixup the
822 * transient state if it does a trylock or leaves the lock
823 * function due to a signal or timeout.
824 *
825 * - @task acquires the lock and there are no other
826 * waiters. This is undone in rt_mutex_set_owner(@task) at
827 * the end of this function.
828 */
829 mark_rt_mutex_waiters(lock);
830
831 /*
832 * If @lock has an owner, give up.
833 */
834 if (rt_mutex_owner(lock))
835 return 0;
836
837 /*
838 * If @waiter != NULL, @task has already enqueued the waiter
839 * into @lock waiter tree. If @waiter == NULL then this is a
840 * trylock attempt.
841 */
842 if (waiter) {
843 /*
844 * If waiter is not the highest priority waiter of
845 * @lock, give up.
846 */
847 if (waiter != rt_mutex_top_waiter(lock))
848 return 0;
849
850 /*
851 * We can acquire the lock. Remove the waiter from the
852 * lock waiters tree.
853 */
854 rt_mutex_dequeue(lock, waiter);
855
856 } else {
857 /*
858 * If the lock has waiters already we check whether @task is
859 * eligible to take over the lock.
860 *
861 * If there are no other waiters, @task can acquire
862 * the lock. @task->pi_blocked_on is NULL, so it does
863 * not need to be dequeued.
864 */
865 if (rt_mutex_has_waiters(lock)) {
866 /*
867 * If @task->prio is greater than or equal to
868 * the top waiter priority (kernel view),
869 * @task lost.
870 */
871 if (!rt_mutex_waiter_less(task_to_waiter(task),
872 rt_mutex_top_waiter(lock)))
873 return 0;
874
875 /*
876 * The current top waiter stays enqueued. We
877 * don't have to change anything in the lock
878 * waiters order.
879 */
880 } else {
881 /*
882 * No waiters. Take the lock without the
883 * pi_lock dance.@task->pi_blocked_on is NULL
884 * and we have no waiters to enqueue in @task
885 * pi waiters tree.
886 */
887 goto takeit;
888 }
889 }
890
891 /*
892 * Clear @task->pi_blocked_on. Requires protection by
893 * @task->pi_lock. Redundant operation for the @waiter == NULL
894 * case, but conditionals are more expensive than a redundant
895 * store.
896 */
897 raw_spin_lock(&task->pi_lock);
898 task->pi_blocked_on = NULL;
899 /*
900 * Finish the lock acquisition. @task is the new owner. If
901 * other waiters exist we have to insert the highest priority
902 * waiter into @task->pi_waiters tree.
903 */
904 if (rt_mutex_has_waiters(lock))
905 rt_mutex_enqueue_pi(task, rt_mutex_top_waiter(lock));
906 raw_spin_unlock(&task->pi_lock);
907
908 takeit:
909 /* We got the lock. */
910 debug_rt_mutex_lock(lock);
911
912 /*
913 * This either preserves the RT_MUTEX_HAS_WAITERS bit if there
914 * are still waiters or clears it.
915 */
916 rt_mutex_set_owner(lock, task);
917
918 return 1;
919 }
920
921 /*
922 * Task blocks on lock.
923 *
924 * Prepare waiter and propagate pi chain
925 *
926 * This must be called with lock->wait_lock held and interrupts disabled
927 */
928 static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
929 struct rt_mutex_waiter *waiter,
930 struct task_struct *task,
931 enum rtmutex_chainwalk chwalk)
932 {
933 struct task_struct *owner = rt_mutex_owner(lock);
934 struct rt_mutex_waiter *top_waiter = waiter;
935 struct rt_mutex *next_lock;
936 int chain_walk = 0, res;
937
938 lockdep_assert_held(&lock->wait_lock);
939
940 /*
941 * Early deadlock detection. We really don't want the task to
942 * enqueue on itself just to untangle the mess later. It's not
943 * only an optimization. We drop the locks, so another waiter
944 * can come in before the chain walk detects the deadlock. So
945 * the other will detect the deadlock and return -EDEADLOCK,
946 * which is wrong, as the other waiter is not in a deadlock
947 * situation.
948 */
949 if (owner == task)
950 return -EDEADLK;
951
952 raw_spin_lock(&task->pi_lock);
953 waiter->task = task;
954 waiter->lock = lock;
955 waiter->prio = task->prio;
956 waiter->deadline = task->dl.deadline;
957
958 /* Get the top priority waiter on the lock */
959 if (rt_mutex_has_waiters(lock))
960 top_waiter = rt_mutex_top_waiter(lock);
961 rt_mutex_enqueue(lock, waiter);
962
963 task->pi_blocked_on = waiter;
964
965 raw_spin_unlock(&task->pi_lock);
966
967 if (!owner)
968 return 0;
969
970 raw_spin_lock(&owner->pi_lock);
971 if (waiter == rt_mutex_top_waiter(lock)) {
972 rt_mutex_dequeue_pi(owner, top_waiter);
973 rt_mutex_enqueue_pi(owner, waiter);
974
975 rt_mutex_adjust_prio(owner);
976 if (owner->pi_blocked_on)
977 chain_walk = 1;
978 } else if (rt_mutex_cond_detect_deadlock(waiter, chwalk)) {
979 chain_walk = 1;
980 }
981
982 /* Store the lock on which owner is blocked or NULL */
983 next_lock = task_blocked_on_lock(owner);
984
985 raw_spin_unlock(&owner->pi_lock);
986 /*
987 * Even if full deadlock detection is on, if the owner is not
988 * blocked itself, we can avoid finding this out in the chain
989 * walk.
990 */
991 if (!chain_walk || !next_lock)
992 return 0;
993
994 /*
995 * The owner can't disappear while holding a lock,
996 * so the owner struct is protected by wait_lock.
997 * Gets dropped in rt_mutex_adjust_prio_chain()!
998 */
999 get_task_struct(owner);
1000
1001 raw_spin_unlock_irq(&lock->wait_lock);
1002
1003 res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1004 next_lock, waiter, task);
1005
1006 raw_spin_lock_irq(&lock->wait_lock);
1007
1008 return res;
1009 }
1010
1011 /*
1012 * Remove the top waiter from the current tasks pi waiter tree and
1013 * queue it up.
1014 *
1015 * Called with lock->wait_lock held and interrupts disabled.
1016 */
1017 static void mark_wakeup_next_waiter(struct wake_q_head *wake_q,
1018 struct rt_mutex *lock)
1019 {
1020 struct rt_mutex_waiter *waiter;
1021
1022 raw_spin_lock(¤t->pi_lock);
1023
1024 waiter = rt_mutex_top_waiter(lock);
1025
1026 /*
1027 * Remove it from current->pi_waiters and deboost.
1028 *
1029 * We must in fact deboost here in order to ensure we call
1030 * rt_mutex_setprio() to update p->pi_top_task before the
1031 * task unblocks.
1032 */
1033 rt_mutex_dequeue_pi(current, waiter);
1034 rt_mutex_adjust_prio(current);
1035
1036 /*
1037 * As we are waking up the top waiter, and the waiter stays
1038 * queued on the lock until it gets the lock, this lock
1039 * obviously has waiters. Just set the bit here and this has
1040 * the added benefit of forcing all new tasks into the
1041 * slow path making sure no task of lower priority than
1042 * the top waiter can steal this lock.
1043 */
1044 lock->owner = (void *) RT_MUTEX_HAS_WAITERS;
1045
1046 /*
1047 * We deboosted before waking the top waiter task such that we don't
1048 * run two tasks with the 'same' priority (and ensure the
1049 * p->pi_top_task pointer points to a blocked task). This however can
1050 * lead to priority inversion if we would get preempted after the
1051 * deboost but before waking our donor task, hence the preempt_disable()
1052 * before unlock.
1053 *
1054 * Pairs with preempt_enable() in rt_mutex_postunlock();
1055 */
1056 preempt_disable();
1057 wake_q_add(wake_q, waiter->task);
1058 raw_spin_unlock(¤t->pi_lock);
1059 }
1060
1061 /*
1062 * Remove a waiter from a lock and give up
1063 *
1064 * Must be called with lock->wait_lock held and interrupts disabled. I must
1065 * have just failed to try_to_take_rt_mutex().
1066 */
1067 static void remove_waiter(struct rt_mutex *lock,
1068 struct rt_mutex_waiter *waiter)
1069 {
1070 bool is_top_waiter = (waiter == rt_mutex_top_waiter(lock));
1071 struct task_struct *owner = rt_mutex_owner(lock);
1072 struct rt_mutex *next_lock;
1073
1074 lockdep_assert_held(&lock->wait_lock);
1075
1076 raw_spin_lock(¤t->pi_lock);
1077 rt_mutex_dequeue(lock, waiter);
1078 current->pi_blocked_on = NULL;
1079 raw_spin_unlock(¤t->pi_lock);
1080
1081 /*
1082 * Only update priority if the waiter was the highest priority
1083 * waiter of the lock and there is an owner to update.
1084 */
1085 if (!owner || !is_top_waiter)
1086 return;
1087
1088 raw_spin_lock(&owner->pi_lock);
1089
1090 rt_mutex_dequeue_pi(owner, waiter);
1091
1092 if (rt_mutex_has_waiters(lock))
1093 rt_mutex_enqueue_pi(owner, rt_mutex_top_waiter(lock));
1094
1095 rt_mutex_adjust_prio(owner);
1096
1097 /* Store the lock on which owner is blocked or NULL */
1098 next_lock = task_blocked_on_lock(owner);
1099
1100 raw_spin_unlock(&owner->pi_lock);
1101
1102 /*
1103 * Don't walk the chain, if the owner task is not blocked
1104 * itself.
1105 */
1106 if (!next_lock)
1107 return;
1108
1109 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1110 get_task_struct(owner);
1111
1112 raw_spin_unlock_irq(&lock->wait_lock);
1113
1114 rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1115 next_lock, NULL, current);
1116
1117 raw_spin_lock_irq(&lock->wait_lock);
1118 }
1119
1120 /*
1121 * Recheck the pi chain, in case we got a priority setting
1122 *
1123 * Called from sched_setscheduler
1124 */
1125 void rt_mutex_adjust_pi(struct task_struct *task)
1126 {
1127 struct rt_mutex_waiter *waiter;
1128 struct rt_mutex *next_lock;
1129 unsigned long flags;
1130
1131 raw_spin_lock_irqsave(&task->pi_lock, flags);
1132
1133 waiter = task->pi_blocked_on;
1134 if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
1135 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1136 return;
1137 }
1138 next_lock = waiter->lock;
1139 raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1140
1141 /* gets dropped in rt_mutex_adjust_prio_chain()! */
1142 get_task_struct(task);
1143
1144 rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1145 next_lock, NULL, task);
1146 }
1147
1148 void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
1149 {
1150 debug_rt_mutex_init_waiter(waiter);
1151 RB_CLEAR_NODE(&waiter->pi_tree_entry);
1152 RB_CLEAR_NODE(&waiter->tree_entry);
1153 waiter->task = NULL;
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 */
1166 static 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 (likely(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
1206 static 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 */
1229 static int __sched
1230 rt_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 rt_mutex_init_waiter(&waiter);
1239
1240 /*
1241 * Technically we could use raw_spin_[un]lock_irq() here, but this can
1242 * be called in early boot if the cmpxchg() fast path is disabled
1243 * (debug, no architecture support). In this case we will acquire the
1244 * rtmutex with lock->wait_lock held. But we cannot unconditionally
1245 * enable interrupts in that early boot case. So we need to use the
1246 * irqsave/restore variants.
1247 */
1248 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1249
1250 /* Try to acquire the lock again: */
1251 if (try_to_take_rt_mutex(lock, current, NULL)) {
1252 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1253 return 0;
1254 }
1255
1256 set_current_state(state);
1257
1258 /* Setup the timer, when timeout != NULL */
1259 if (unlikely(timeout))
1260 hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1261
1262 ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1263
1264 if (likely(!ret))
1265 /* sleep on the mutex */
1266 ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1267
1268 if (unlikely(ret)) {
1269 __set_current_state(TASK_RUNNING);
1270 remove_waiter(lock, &waiter);
1271 rt_mutex_handle_deadlock(ret, chwalk, &waiter);
1272 }
1273
1274 /*
1275 * try_to_take_rt_mutex() sets the waiter bit
1276 * unconditionally. We might have to fix that up.
1277 */
1278 fixup_rt_mutex_waiters(lock);
1279
1280 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1281
1282 /* Remove pending timer: */
1283 if (unlikely(timeout))
1284 hrtimer_cancel(&timeout->timer);
1285
1286 debug_rt_mutex_free_waiter(&waiter);
1287
1288 return ret;
1289 }
1290
1291 static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
1292 {
1293 int ret = try_to_take_rt_mutex(lock, current, NULL);
1294
1295 /*
1296 * try_to_take_rt_mutex() sets the lock waiters bit
1297 * unconditionally. Clean this up.
1298 */
1299 fixup_rt_mutex_waiters(lock);
1300
1301 return ret;
1302 }
1303
1304 /*
1305 * Slow path try-lock function:
1306 */
1307 static inline int rt_mutex_slowtrylock(struct rt_mutex *lock)
1308 {
1309 unsigned long flags;
1310 int ret;
1311
1312 /*
1313 * If the lock already has an owner we fail to get the lock.
1314 * This can be done without taking the @lock->wait_lock as
1315 * it is only being read, and this is a trylock anyway.
1316 */
1317 if (rt_mutex_owner(lock))
1318 return 0;
1319
1320 /*
1321 * The mutex has currently no owner. Lock the wait lock and try to
1322 * acquire the lock. We use irqsave here to support early boot calls.
1323 */
1324 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1325
1326 ret = __rt_mutex_slowtrylock(lock);
1327
1328 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1329
1330 return ret;
1331 }
1332
1333 /*
1334 * Slow path to release a rt-mutex.
1335 *
1336 * Return whether the current task needs to call rt_mutex_postunlock().
1337 */
1338 static bool __sched rt_mutex_slowunlock(struct rt_mutex *lock,
1339 struct wake_q_head *wake_q)
1340 {
1341 unsigned long flags;
1342
1343 /* irqsave required to support early boot calls */
1344 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1345
1346 debug_rt_mutex_unlock(lock);
1347
1348 /*
1349 * We must be careful here if the fast path is enabled. If we
1350 * have no waiters queued we cannot set owner to NULL here
1351 * because of:
1352 *
1353 * foo->lock->owner = NULL;
1354 * rtmutex_lock(foo->lock); <- fast path
1355 * free = atomic_dec_and_test(foo->refcnt);
1356 * rtmutex_unlock(foo->lock); <- fast path
1357 * if (free)
1358 * kfree(foo);
1359 * raw_spin_unlock(foo->lock->wait_lock);
1360 *
1361 * So for the fastpath enabled kernel:
1362 *
1363 * Nothing can set the waiters bit as long as we hold
1364 * lock->wait_lock. So we do the following sequence:
1365 *
1366 * owner = rt_mutex_owner(lock);
1367 * clear_rt_mutex_waiters(lock);
1368 * raw_spin_unlock(&lock->wait_lock);
1369 * if (cmpxchg(&lock->owner, owner, 0) == owner)
1370 * return;
1371 * goto retry;
1372 *
1373 * The fastpath disabled variant is simple as all access to
1374 * lock->owner is serialized by lock->wait_lock:
1375 *
1376 * lock->owner = NULL;
1377 * raw_spin_unlock(&lock->wait_lock);
1378 */
1379 while (!rt_mutex_has_waiters(lock)) {
1380 /* Drops lock->wait_lock ! */
1381 if (unlock_rt_mutex_safe(lock, flags) == true)
1382 return false;
1383 /* Relock the rtmutex and try again */
1384 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1385 }
1386
1387 /*
1388 * The wakeup next waiter path does not suffer from the above
1389 * race. See the comments there.
1390 *
1391 * Queue the next waiter for wakeup once we release the wait_lock.
1392 */
1393 mark_wakeup_next_waiter(wake_q, lock);
1394 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1395
1396 return true; /* call rt_mutex_postunlock() */
1397 }
1398
1399 /*
1400 * debug aware fast / slowpath lock,trylock,unlock
1401 *
1402 * The atomic acquire/release ops are compiled away, when either the
1403 * architecture does not support cmpxchg or when debugging is enabled.
1404 */
1405 static inline int
1406 rt_mutex_fastlock(struct rt_mutex *lock, int state,
1407 int (*slowfn)(struct rt_mutex *lock, int state,
1408 struct hrtimer_sleeper *timeout,
1409 enum rtmutex_chainwalk chwalk))
1410 {
1411 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1412 return 0;
1413
1414 return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1415 }
1416
1417 static inline int
1418 rt_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 return 0;
1428
1429 return slowfn(lock, state, timeout, chwalk);
1430 }
1431
1432 static inline int
1433 rt_mutex_fasttrylock(struct rt_mutex *lock,
1434 int (*slowfn)(struct rt_mutex *lock))
1435 {
1436 if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1437 return 1;
1438
1439 return slowfn(lock);
1440 }
1441
1442 /*
1443 * Performs the wakeup of the the top-waiter and re-enables preemption.
1444 */
1445 void rt_mutex_postunlock(struct wake_q_head *wake_q)
1446 {
1447 wake_up_q(wake_q);
1448
1449 /* Pairs with preempt_disable() in rt_mutex_slowunlock() */
1450 preempt_enable();
1451 }
1452
1453 static inline void
1454 rt_mutex_fastunlock(struct rt_mutex *lock,
1455 bool (*slowfn)(struct rt_mutex *lock,
1456 struct wake_q_head *wqh))
1457 {
1458 DEFINE_WAKE_Q(wake_q);
1459
1460 if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1461 return;
1462
1463 if (slowfn(lock, &wake_q))
1464 rt_mutex_postunlock(&wake_q);
1465 }
1466
1467 static inline void __rt_mutex_lock(struct rt_mutex *lock, unsigned int subclass)
1468 {
1469 might_sleep();
1470
1471 mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
1472 rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, rt_mutex_slowlock);
1473 }
1474
1475 #ifdef CONFIG_DEBUG_LOCK_ALLOC
1476 /**
1477 * rt_mutex_lock_nested - lock a rt_mutex
1478 *
1479 * @lock: the rt_mutex to be locked
1480 * @subclass: the lockdep subclass
1481 */
1482 void __sched rt_mutex_lock_nested(struct rt_mutex *lock, unsigned int subclass)
1483 {
1484 __rt_mutex_lock(lock, subclass);
1485 }
1486 EXPORT_SYMBOL_GPL(rt_mutex_lock_nested);
1487
1488 #else /* !CONFIG_DEBUG_LOCK_ALLOC */
1489
1490 /**
1491 * rt_mutex_lock - lock a rt_mutex
1492 *
1493 * @lock: the rt_mutex to be locked
1494 */
1495 void __sched rt_mutex_lock(struct rt_mutex *lock)
1496 {
1497 __rt_mutex_lock(lock, 0);
1498 }
1499 EXPORT_SYMBOL_GPL(rt_mutex_lock);
1500 #endif
1501
1502 /**
1503 * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
1504 *
1505 * @lock: the rt_mutex to be locked
1506 *
1507 * Returns:
1508 * 0 on success
1509 * -EINTR when interrupted by a signal
1510 */
1511 int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1512 {
1513 int ret;
1514
1515 might_sleep();
1516
1517 mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1518 ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1519 if (ret)
1520 mutex_release(&lock->dep_map, 1, _RET_IP_);
1521
1522 return ret;
1523 }
1524 EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1525
1526 /*
1527 * Futex variant, must not use fastpath.
1528 */
1529 int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
1530 {
1531 return rt_mutex_slowtrylock(lock);
1532 }
1533
1534 int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
1535 {
1536 return __rt_mutex_slowtrylock(lock);
1537 }
1538
1539 /**
1540 * rt_mutex_timed_lock - lock a rt_mutex interruptible
1541 * the timeout structure is provided
1542 * by the caller
1543 *
1544 * @lock: the rt_mutex to be locked
1545 * @timeout: timeout structure or NULL (no timeout)
1546 *
1547 * Returns:
1548 * 0 on success
1549 * -EINTR when interrupted by a signal
1550 * -ETIMEDOUT when the timeout expired
1551 */
1552 int
1553 rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1554 {
1555 int ret;
1556
1557 might_sleep();
1558
1559 mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1560 ret = rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
1561 RT_MUTEX_MIN_CHAINWALK,
1562 rt_mutex_slowlock);
1563 if (ret)
1564 mutex_release(&lock->dep_map, 1, _RET_IP_);
1565
1566 return ret;
1567 }
1568 EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
1569
1570 /**
1571 * rt_mutex_trylock - try to lock a rt_mutex
1572 *
1573 * @lock: the rt_mutex to be locked
1574 *
1575 * This function can only be called in thread context. It's safe to
1576 * call it from atomic regions, but not from hard interrupt or soft
1577 * interrupt context.
1578 *
1579 * Returns 1 on success and 0 on contention
1580 */
1581 int __sched rt_mutex_trylock(struct rt_mutex *lock)
1582 {
1583 int ret;
1584
1585 if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
1586 return 0;
1587
1588 ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1589 if (ret)
1590 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1591
1592 return ret;
1593 }
1594 EXPORT_SYMBOL_GPL(rt_mutex_trylock);
1595
1596 /**
1597 * rt_mutex_unlock - unlock a rt_mutex
1598 *
1599 * @lock: the rt_mutex to be unlocked
1600 */
1601 void __sched rt_mutex_unlock(struct rt_mutex *lock)
1602 {
1603 mutex_release(&lock->dep_map, 1, _RET_IP_);
1604 rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1605 }
1606 EXPORT_SYMBOL_GPL(rt_mutex_unlock);
1607
1608 /**
1609 * Futex variant, that since futex variants do not use the fast-path, can be
1610 * simple and will not need to retry.
1611 */
1612 bool __sched __rt_mutex_futex_unlock(struct rt_mutex *lock,
1613 struct wake_q_head *wake_q)
1614 {
1615 lockdep_assert_held(&lock->wait_lock);
1616
1617 debug_rt_mutex_unlock(lock);
1618
1619 if (!rt_mutex_has_waiters(lock)) {
1620 lock->owner = NULL;
1621 return false; /* done */
1622 }
1623
1624 /*
1625 * We've already deboosted, mark_wakeup_next_waiter() will
1626 * retain preempt_disabled when we drop the wait_lock, to
1627 * avoid inversion prior to the wakeup. preempt_disable()
1628 * therein pairs with rt_mutex_postunlock().
1629 */
1630 mark_wakeup_next_waiter(wake_q, lock);
1631
1632 return true; /* call postunlock() */
1633 }
1634
1635 void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
1636 {
1637 DEFINE_WAKE_Q(wake_q);
1638 unsigned long flags;
1639 bool postunlock;
1640
1641 raw_spin_lock_irqsave(&lock->wait_lock, flags);
1642 postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
1643 raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1644
1645 if (postunlock)
1646 rt_mutex_postunlock(&wake_q);
1647 }
1648
1649 /**
1650 * rt_mutex_destroy - mark a mutex unusable
1651 * @lock: the mutex to be destroyed
1652 *
1653 * This function marks the mutex uninitialized, and any subsequent
1654 * use of the mutex is forbidden. The mutex must not be locked when
1655 * this function is called.
1656 */
1657 void rt_mutex_destroy(struct rt_mutex *lock)
1658 {
1659 WARN_ON(rt_mutex_is_locked(lock));
1660 #ifdef CONFIG_DEBUG_RT_MUTEXES
1661 lock->magic = NULL;
1662 #endif
1663 }
1664 EXPORT_SYMBOL_GPL(rt_mutex_destroy);
1665
1666 /**
1667 * __rt_mutex_init - initialize the rt lock
1668 *
1669 * @lock: the rt lock to be initialized
1670 *
1671 * Initialize the rt lock to unlocked state.
1672 *
1673 * Initializing of a locked rt lock is not allowed
1674 */
1675 void __rt_mutex_init(struct rt_mutex *lock, const char *name,
1676 struct lock_class_key *key)
1677 {
1678 lock->owner = NULL;
1679 raw_spin_lock_init(&lock->wait_lock);
1680 lock->waiters = RB_ROOT_CACHED;
1681
1682 if (name && key)
1683 debug_rt_mutex_init(lock, name, key);
1684 }
1685 EXPORT_SYMBOL_GPL(__rt_mutex_init);
1686
1687 /**
1688 * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1689 * proxy owner
1690 *
1691 * @lock: the rt_mutex to be locked
1692 * @proxy_owner:the task to set as owner
1693 *
1694 * No locking. Caller has to do serializing itself
1695 *
1696 * Special API call for PI-futex support. This initializes the rtmutex and
1697 * assigns it to @proxy_owner. Concurrent operations on the rtmutex are not
1698 * possible at this point because the pi_state which contains the rtmutex
1699 * is not yet visible to other tasks.
1700 */
1701 void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1702 struct task_struct *proxy_owner)
1703 {
1704 __rt_mutex_init(lock, NULL, NULL);
1705 debug_rt_mutex_proxy_lock(lock, proxy_owner);
1706 rt_mutex_set_owner(lock, proxy_owner);
1707 }
1708
1709 /**
1710 * rt_mutex_proxy_unlock - release a lock on behalf of owner
1711 *
1712 * @lock: the rt_mutex to be locked
1713 *
1714 * No locking. Caller has to do serializing itself
1715 *
1716 * Special API call for PI-futex support. This merrily cleans up the rtmutex
1717 * (debugging) state. Concurrent operations on this rt_mutex are not
1718 * possible because it belongs to the pi_state which is about to be freed
1719 * and it is not longer visible to other tasks.
1720 */
1721 void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1722 struct task_struct *proxy_owner)
1723 {
1724 debug_rt_mutex_proxy_unlock(lock);
1725 rt_mutex_set_owner(lock, NULL);
1726 }
1727
1728 /**
1729 * __rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1730 * @lock: the rt_mutex to take
1731 * @waiter: the pre-initialized rt_mutex_waiter
1732 * @task: the task to prepare
1733 *
1734 * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
1735 * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
1736 *
1737 * NOTE: does _NOT_ remove the @waiter on failure; must either call
1738 * rt_mutex_wait_proxy_lock() or rt_mutex_cleanup_proxy_lock() after this.
1739 *
1740 * Returns:
1741 * 0 - task blocked on lock
1742 * 1 - acquired the lock for task, caller should wake it up
1743 * <0 - error
1744 *
1745 * Special API call for PI-futex support.
1746 */
1747 int __rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1748 struct rt_mutex_waiter *waiter,
1749 struct task_struct *task)
1750 {
1751 int ret;
1752
1753 lockdep_assert_held(&lock->wait_lock);
1754
1755 if (try_to_take_rt_mutex(lock, task, NULL))
1756 return 1;
1757
1758 /* We enforce deadlock detection for futexes */
1759 ret = task_blocks_on_rt_mutex(lock, waiter, task,
1760 RT_MUTEX_FULL_CHAINWALK);
1761
1762 if (ret && !rt_mutex_owner(lock)) {
1763 /*
1764 * Reset the return value. We might have
1765 * returned with -EDEADLK and the owner
1766 * released the lock while we were walking the
1767 * pi chain. Let the waiter sort it out.
1768 */
1769 ret = 0;
1770 }
1771
1772 debug_rt_mutex_print_deadlock(waiter);
1773
1774 return ret;
1775 }
1776
1777 /**
1778 * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1779 * @lock: the rt_mutex to take
1780 * @waiter: the pre-initialized rt_mutex_waiter
1781 * @task: the task to prepare
1782 *
1783 * Starts the rt_mutex acquire; it enqueues the @waiter and does deadlock
1784 * detection. It does not wait, see rt_mutex_wait_proxy_lock() for that.
1785 *
1786 * NOTE: unlike __rt_mutex_start_proxy_lock this _DOES_ remove the @waiter
1787 * on failure.
1788 *
1789 * Returns:
1790 * 0 - task blocked on lock
1791 * 1 - acquired the lock for task, caller should wake it up
1792 * <0 - error
1793 *
1794 * Special API call for PI-futex support.
1795 */
1796 int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1797 struct rt_mutex_waiter *waiter,
1798 struct task_struct *task)
1799 {
1800 int ret;
1801
1802 raw_spin_lock_irq(&lock->wait_lock);
1803 ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
1804 if (unlikely(ret))
1805 remove_waiter(lock, waiter);
1806 raw_spin_unlock_irq(&lock->wait_lock);
1807
1808 return ret;
1809 }
1810
1811 /**
1812 * rt_mutex_next_owner - return the next owner of the lock
1813 *
1814 * @lock: the rt lock query
1815 *
1816 * Returns the next owner of the lock or NULL
1817 *
1818 * Caller has to serialize against other accessors to the lock
1819 * itself.
1820 *
1821 * Special API call for PI-futex support
1822 */
1823 struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1824 {
1825 if (!rt_mutex_has_waiters(lock))
1826 return NULL;
1827
1828 return rt_mutex_top_waiter(lock)->task;
1829 }
1830
1831 /**
1832 * rt_mutex_wait_proxy_lock() - Wait for lock acquisition
1833 * @lock: the rt_mutex we were woken on
1834 * @to: the timeout, null if none. hrtimer should already have
1835 * been started.
1836 * @waiter: the pre-initialized rt_mutex_waiter
1837 *
1838 * Wait for the the lock acquisition started on our behalf by
1839 * rt_mutex_start_proxy_lock(). Upon failure, the caller must call
1840 * rt_mutex_cleanup_proxy_lock().
1841 *
1842 * Returns:
1843 * 0 - success
1844 * <0 - error, one of -EINTR, -ETIMEDOUT
1845 *
1846 * Special API call for PI-futex support
1847 */
1848 int rt_mutex_wait_proxy_lock(struct rt_mutex *lock,
1849 struct hrtimer_sleeper *to,
1850 struct rt_mutex_waiter *waiter)
1851 {
1852 int ret;
1853
1854 raw_spin_lock_irq(&lock->wait_lock);
1855 /* sleep on the mutex */
1856 set_current_state(TASK_INTERRUPTIBLE);
1857 ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1858 /*
1859 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1860 * have to fix that up.
1861 */
1862 fixup_rt_mutex_waiters(lock);
1863 raw_spin_unlock_irq(&lock->wait_lock);
1864
1865 return ret;
1866 }
1867
1868 /**
1869 * rt_mutex_cleanup_proxy_lock() - Cleanup failed lock acquisition
1870 * @lock: the rt_mutex we were woken on
1871 * @waiter: the pre-initialized rt_mutex_waiter
1872 *
1873 * Attempt to clean up after a failed __rt_mutex_start_proxy_lock() or
1874 * rt_mutex_wait_proxy_lock().
1875 *
1876 * Unless we acquired the lock; we're still enqueued on the wait-list and can
1877 * in fact still be granted ownership until we're removed. Therefore we can
1878 * find we are in fact the owner and must disregard the
1879 * rt_mutex_wait_proxy_lock() failure.
1880 *
1881 * Returns:
1882 * true - did the cleanup, we done.
1883 * false - we acquired the lock after rt_mutex_wait_proxy_lock() returned,
1884 * caller should disregards its return value.
1885 *
1886 * Special API call for PI-futex support
1887 */
1888 bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
1889 struct rt_mutex_waiter *waiter)
1890 {
1891 bool cleanup = false;
1892
1893 raw_spin_lock_irq(&lock->wait_lock);
1894 /*
1895 * Do an unconditional try-lock, this deals with the lock stealing
1896 * state where __rt_mutex_futex_unlock() -> mark_wakeup_next_waiter()
1897 * sets a NULL owner.
1898 *
1899 * We're not interested in the return value, because the subsequent
1900 * test on rt_mutex_owner() will infer that. If the trylock succeeded,
1901 * we will own the lock and it will have removed the waiter. If we
1902 * failed the trylock, we're still not owner and we need to remove
1903 * ourselves.
1904 */
1905 try_to_take_rt_mutex(lock, current, waiter);
1906 /*
1907 * Unless we're the owner; we're still enqueued on the wait_list.
1908 * So check if we became owner, if not, take us off the wait_list.
1909 */
1910 if (rt_mutex_owner(lock) != current) {
1911 remove_waiter(lock, waiter);
1912 cleanup = true;
1913 }
1914 /*
1915 * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1916 * have to fix that up.
1917 */
1918 fixup_rt_mutex_waiters(lock);
1919
1920 raw_spin_unlock_irq(&lock->wait_lock);
1921
1922 return cleanup;
1923 }