Branch data Line data Source code
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 : 0 : unsigned long val = (unsigned long)owner;
56 : :
57 [ # # # # : 0 : if (rt_mutex_has_waiters(lock))
# # ]
58 : 0 : val |= RT_MUTEX_HAS_WAITERS;
59 : :
60 : 0 : lock->owner = (struct task_struct *)val;
61 : : }
62 : :
63 : : static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
64 : : {
65 : 0 : lock->owner = (struct task_struct *)
66 : 0 : ((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 [ # # # # : 0 : 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 [ # # # # : 0 : if (owner & RT_MUTEX_HAS_WAITERS)
# # # # ]
136 : 0 : 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 : 0 : static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
154 : : {
155 : 0 : unsigned long owner, *p = (unsigned long *) &lock->owner;
156 : :
157 : : do {
158 : 0 : owner = *p;
159 [ # # ]: 0 : } while (cmpxchg_relaxed(p, owner,
160 : : owner | RT_MUTEX_HAS_WAITERS) != owner);
161 : 0 : }
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 : 0 : 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 : 0 : 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 : 0 : 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 [ # # # # : 0 : 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 [ # # # # : 0 : if (dl_prio(left->prio))
# # ]
248 : 0 : 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 [ # # # # ]: 0 : 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 [ # # # # ]: 0 : if (dl_prio(left->prio))
267 : 0 : return left->deadline == right->deadline;
268 : :
269 : : return 1;
270 : : }
271 : :
272 : : static void
273 : 0 : rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
274 : : {
275 : 0 : 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 [ # # ]: 0 : while (*link) {
281 : : parent = *link;
282 : : entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
283 [ # # ]: 0 : if (rt_mutex_waiter_less(waiter, entry)) {
284 : 0 : link = &parent->rb_left;
285 : : } else {
286 : 0 : link = &parent->rb_right;
287 : : leftmost = false;
288 : : }
289 : : }
290 : :
291 : 0 : rb_link_node(&waiter->tree_entry, parent, link);
292 : : rb_insert_color_cached(&waiter->tree_entry, &lock->waiters, leftmost);
293 : 0 : }
294 : :
295 : : static void
296 : : rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
297 : : {
298 [ # # # # : 0 : if (RB_EMPTY_NODE(&waiter->tree_entry))
# # ]
299 : : return;
300 : :
301 : 0 : rb_erase_cached(&waiter->tree_entry, &lock->waiters);
302 : 0 : RB_CLEAR_NODE(&waiter->tree_entry);
303 : : }
304 : :
305 : : static void
306 : 0 : rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
307 : : {
308 : 0 : 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 [ # # ]: 0 : while (*link) {
314 : : parent = *link;
315 : : entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
316 [ # # ]: 0 : if (rt_mutex_waiter_less(waiter, entry)) {
317 : 0 : link = &parent->rb_left;
318 : : } else {
319 : 0 : link = &parent->rb_right;
320 : : leftmost = false;
321 : : }
322 : : }
323 : :
324 : 0 : rb_link_node(&waiter->pi_tree_entry, parent, link);
325 : : rb_insert_color_cached(&waiter->pi_tree_entry, &task->pi_waiters, leftmost);
326 : 0 : }
327 : :
328 : : static void
329 : : rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
330 : : {
331 [ # # # # : 0 : if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
# # # # #
# ]
332 : : return;
333 : :
334 : 0 : rb_erase_cached(&waiter->pi_tree_entry, &task->pi_waiters);
335 : 0 : 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 [ # # # # : 0 : if (task_has_pi_waiters(p))
# # # # #
# ]
345 : 0 : pi_task = task_top_pi_waiter(p)->task;
346 : :
347 : 0 : 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 [ # # # # : 0 : 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 : 0 : 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 [ # # ]: 0 : 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 [ # # ]: 0 : if (prev_max != max_lock_depth) {
483 : 0 : prev_max = max_lock_depth;
484 : 0 : printk(KERN_WARNING "Maximum lock depth %d reached "
485 : : "task: %s (%d)\n", max_lock_depth,
486 : 0 : top_task->comm, task_pid_nr(top_task));
487 : : }
488 : 0 : put_task_struct(task);
489 : :
490 : 0 : 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 : 0 : raw_spin_lock_irq(&task->pi_lock);
504 : :
505 : : /*
506 : : * [2] Get the waiter on which @task is blocked on.
507 : : */
508 : 0 : 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 [ # # ]: 0 : 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 [ # # # # ]: 0 : 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 [ # # ]: 0 : 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 [ # # ]: 0 : if (top_waiter) {
547 [ # # ]: 0 : 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 [ # # ]: 0 : if (top_waiter != task_top_pi_waiter(task)) {
556 [ # # ]: 0 : 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 [ # # ]: 0 : if (rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
571 [ # # ]: 0 : 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 [ # # ]: 0 : if (!raw_spin_trylock(&lock->wait_lock)) {
587 : 0 : raw_spin_unlock_irq(&task->pi_lock);
588 : 0 : cpu_relax();
589 : 0 : 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 [ # # # # ]: 0 : 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 : 0 : 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 [ # # ]: 0 : if (!requeue) {
615 : : /*
616 : : * No requeue[7] here. Just release @task [8]
617 : : */
618 : : raw_spin_unlock(&task->pi_lock);
619 : 0 : 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 [ # # ]: 0 : if (!rt_mutex_owner(lock)) {
626 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
627 : 0 : 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 : 0 : 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 : 0 : top_waiter = rt_mutex_top_waiter(lock);
645 : :
646 : : /* [13] Drop locks */
647 : : raw_spin_unlock(&task->pi_lock);
648 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
649 : :
650 : : /* If owner is not blocked, end of chain. */
651 [ # # ]: 0 : 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 : 0 : 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 : 0 : waiter->prio = task->prio;
683 : 0 : waiter->deadline = task->dl.deadline;
684 : :
685 : 0 : rt_mutex_enqueue(lock, waiter);
686 : :
687 : : /* [8] Release the task */
688 : : raw_spin_unlock(&task->pi_lock);
689 : 0 : 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 [ # # ]: 0 : 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 [ # # ]: 0 : if (prerequeue_top_waiter != rt_mutex_top_waiter(lock))
705 : 0 : wake_up_process(rt_mutex_top_waiter(lock)->task);
706 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
707 : 0 : 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 : 0 : raw_spin_lock(&task->pi_lock);
713 : :
714 : : /* [11] requeue the pi waiters if necessary */
715 [ # # ]: 0 : 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 : 0 : rt_mutex_enqueue_pi(task, waiter);
724 : : rt_mutex_adjust_prio(task);
725 : :
726 [ # # ]: 0 : } 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 : 0 : waiter = rt_mutex_top_waiter(lock);
739 : 0 : 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 : 0 : top_waiter = rt_mutex_top_waiter(lock);
764 : :
765 : : /* [13] Drop the locks */
766 : : raw_spin_unlock(&task->pi_lock);
767 : 0 : 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 [ # # ]: 0 : 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 [ # # ]: 0 : if (!detect_deadlock && waiter != top_waiter)
785 : : goto out_put_task;
786 : :
787 : : goto again;
788 : :
789 : : out_unlock_pi:
790 : 0 : raw_spin_unlock_irq(&task->pi_lock);
791 : : out_put_task:
792 : 0 : put_task_struct(task);
793 : :
794 : 0 : 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 : 0 : 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 : 0 : mark_rt_mutex_waiters(lock);
830 : :
831 : : /*
832 : : * If @lock has an owner, give up.
833 : : */
834 [ # # ]: 0 : 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 [ # # ]: 0 : if (waiter) {
843 : : /*
844 : : * If waiter is not the highest priority waiter of
845 : : * @lock, give up.
846 : : */
847 [ # # ]: 0 : 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 [ # # ]: 0 : 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 [ # # ]: 0 : 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 : 0 : raw_spin_lock(&task->pi_lock);
898 : 0 : 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 [ # # ]: 0 : if (rt_mutex_has_waiters(lock))
905 : 0 : 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 : 0 : 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 : 0 : 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 [ # # ]: 0 : if (owner == task)
950 : : return -EDEADLK;
951 : :
952 : 0 : raw_spin_lock(&task->pi_lock);
953 : 0 : waiter->task = task;
954 : 0 : waiter->lock = lock;
955 : 0 : waiter->prio = task->prio;
956 : 0 : waiter->deadline = task->dl.deadline;
957 : :
958 : : /* Get the top priority waiter on the lock */
959 [ # # ]: 0 : if (rt_mutex_has_waiters(lock))
960 : 0 : top_waiter = rt_mutex_top_waiter(lock);
961 : 0 : rt_mutex_enqueue(lock, waiter);
962 : :
963 : 0 : task->pi_blocked_on = waiter;
964 : :
965 : : raw_spin_unlock(&task->pi_lock);
966 : :
967 [ # # ]: 0 : if (!owner)
968 : : return 0;
969 : :
970 : 0 : raw_spin_lock(&owner->pi_lock);
971 [ # # ]: 0 : if (waiter == rt_mutex_top_waiter(lock)) {
972 : : rt_mutex_dequeue_pi(owner, top_waiter);
973 : 0 : rt_mutex_enqueue_pi(owner, waiter);
974 : :
975 : : rt_mutex_adjust_prio(owner);
976 [ # # ]: 0 : if (owner->pi_blocked_on)
977 : : chain_walk = 1;
978 [ # # ]: 0 : } 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 [ # # ]: 0 : 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 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
1002 : :
1003 : 0 : res = rt_mutex_adjust_prio_chain(owner, chwalk, lock,
1004 : : next_lock, waiter, task);
1005 : :
1006 : 0 : raw_spin_lock_irq(&lock->wait_lock);
1007 : :
1008 : 0 : 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 : 0 : 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 : 0 : raw_spin_lock(¤t->pi_lock);
1023 : :
1024 : 0 : 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 : 0 : rt_mutex_dequeue_pi(current, waiter);
1034 : 0 : 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 : 0 : 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 : 0 : preempt_disable();
1057 : 0 : wake_q_add(wake_q, waiter->task);
1058 : 0 : raw_spin_unlock(¤t->pi_lock);
1059 : 0 : }
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 : 0 : static void remove_waiter(struct rt_mutex *lock,
1068 : : struct rt_mutex_waiter *waiter)
1069 : : {
1070 : 0 : 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 : 0 : raw_spin_lock(¤t->pi_lock);
1077 : : rt_mutex_dequeue(lock, waiter);
1078 : 0 : current->pi_blocked_on = NULL;
1079 : 0 : 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 [ # # ]: 0 : if (!owner || !is_top_waiter)
1086 : : return;
1087 : :
1088 : 0 : raw_spin_lock(&owner->pi_lock);
1089 : :
1090 : : rt_mutex_dequeue_pi(owner, waiter);
1091 : :
1092 [ # # ]: 0 : if (rt_mutex_has_waiters(lock))
1093 : 0 : 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 [ # # ]: 0 : if (!next_lock)
1107 : : return;
1108 : :
1109 : : /* gets dropped in rt_mutex_adjust_prio_chain()! */
1110 : : get_task_struct(owner);
1111 : :
1112 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
1113 : :
1114 : 0 : rt_mutex_adjust_prio_chain(owner, RT_MUTEX_MIN_CHAINWALK, lock,
1115 : : next_lock, NULL, current);
1116 : :
1117 : 0 : 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 : 1035 : 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 : 1035 : raw_spin_lock_irqsave(&task->pi_lock, flags);
1132 : :
1133 : 1035 : waiter = task->pi_blocked_on;
1134 [ - + # # ]: 1035 : if (!waiter || rt_mutex_waiter_equal(waiter, task_to_waiter(task))) {
1135 : 1035 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
1136 : 2070 : return;
1137 : : }
1138 : 0 : next_lock = waiter->lock;
1139 : 0 : 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 : 0 : rt_mutex_adjust_prio_chain(task, RT_MUTEX_MIN_CHAINWALK, NULL,
1145 : : next_lock, NULL, task);
1146 : : }
1147 : :
1148 : 0 : void rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
1149 : : {
1150 : : debug_rt_mutex_init_waiter(waiter);
1151 : 0 : RB_CLEAR_NODE(&waiter->pi_tree_entry);
1152 : 0 : RB_CLEAR_NODE(&waiter->tree_entry);
1153 : 0 : waiter->task = NULL;
1154 : 0 : }
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 : 0 : __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 [ # # ]: 0 : 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 [ # # ]: 0 : if (likely(state == TASK_INTERRUPTIBLE)) {
1183 : : /* Signal pending? */
1184 [ # # ]: 0 : if (signal_pending(current))
1185 : : ret = -EINTR;
1186 [ # # # # ]: 0 : if (timeout && !timeout->task)
1187 : : ret = -ETIMEDOUT;
1188 [ # # ]: 0 : if (ret)
1189 : : break;
1190 : : }
1191 : :
1192 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
1193 : :
1194 : : debug_rt_mutex_print_deadlock(waiter);
1195 : :
1196 : 0 : schedule();
1197 : :
1198 : 0 : raw_spin_lock_irq(&lock->wait_lock);
1199 : 0 : set_current_state(state);
1200 : 0 : }
1201 : :
1202 : 0 : __set_current_state(TASK_RUNNING);
1203 : 0 : return ret;
1204 : : }
1205 : :
1206 : 0 : 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 [ # # ]: 0 : if (res != -EDEADLOCK || detect_deadlock)
1214 : 0 : return;
1215 : :
1216 : : /*
1217 : : * Yell lowdly and stop the task right here.
1218 : : */
1219 : : rt_mutex_print_deadlock(w);
1220 : : while (1) {
1221 : 0 : set_current_state(TASK_INTERRUPTIBLE);
1222 : 0 : schedule();
1223 : 0 : }
1224 : : }
1225 : :
1226 : : /*
1227 : : * Slow path lock function:
1228 : : */
1229 : : static int __sched
1230 : 0 : 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 : 0 : raw_spin_lock_irqsave(&lock->wait_lock, flags);
1249 : :
1250 : : /* Try to acquire the lock again: */
1251 [ # # ]: 0 : if (try_to_take_rt_mutex(lock, current, NULL)) {
1252 : 0 : raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1253 : 0 : return 0;
1254 : : }
1255 : :
1256 : 0 : set_current_state(state);
1257 : :
1258 : : /* Setup the timer, when timeout != NULL */
1259 [ # # ]: 0 : if (unlikely(timeout))
1260 : 0 : hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
1261 : :
1262 : 0 : ret = task_blocks_on_rt_mutex(lock, &waiter, current, chwalk);
1263 : :
1264 [ # # ]: 0 : if (likely(!ret))
1265 : : /* sleep on the mutex */
1266 : 0 : ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
1267 : :
1268 [ # # ]: 0 : if (unlikely(ret)) {
1269 : 0 : __set_current_state(TASK_RUNNING);
1270 : 0 : remove_waiter(lock, &waiter);
1271 : 0 : 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 : 0 : raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1281 : :
1282 : : /* Remove pending timer: */
1283 [ # # ]: 0 : if (unlikely(timeout))
1284 : 0 : hrtimer_cancel(&timeout->timer);
1285 : :
1286 : : debug_rt_mutex_free_waiter(&waiter);
1287 : :
1288 : 0 : return ret;
1289 : : }
1290 : :
1291 : 0 : static inline int __rt_mutex_slowtrylock(struct rt_mutex *lock)
1292 : : {
1293 : 0 : 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 : 0 : return ret;
1302 : : }
1303 : :
1304 : : /*
1305 : : * Slow path try-lock function:
1306 : : */
1307 : 0 : 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 [ # # ]: 0 : 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 : 0 : raw_spin_lock_irqsave(&lock->wait_lock, flags);
1325 : :
1326 : 0 : ret = __rt_mutex_slowtrylock(lock);
1327 : :
1328 : 0 : raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1329 : :
1330 : 0 : 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 : 0 : 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 : 0 : 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 [ # # ]: 0 : while (!rt_mutex_has_waiters(lock)) {
1380 : : /* Drops lock->wait_lock ! */
1381 [ # # ]: 0 : if (unlock_rt_mutex_safe(lock, flags) == true)
1382 : : return false;
1383 : : /* Relock the rtmutex and try again */
1384 : 0 : 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 : 0 : mark_wakeup_next_waiter(wake_q, lock);
1394 : 0 : raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1395 : :
1396 : 0 : 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 : 0 : 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 [ # # ]: 0 : if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1412 : : return 0;
1413 : :
1414 : 0 : return slowfn(lock, state, NULL, RT_MUTEX_MIN_CHAINWALK);
1415 : : }
1416 : :
1417 : : static inline int
1418 : 0 : 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 [ # # # # ]: 0 : if (chwalk == RT_MUTEX_MIN_CHAINWALK &&
1426 : 0 : likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1427 : : return 0;
1428 : :
1429 : 0 : return slowfn(lock, state, timeout, chwalk);
1430 : : }
1431 : :
1432 : : static inline int
1433 : 0 : rt_mutex_fasttrylock(struct rt_mutex *lock,
1434 : : int (*slowfn)(struct rt_mutex *lock))
1435 : : {
1436 [ # # ]: 0 : if (likely(rt_mutex_cmpxchg_acquire(lock, NULL, current)))
1437 : : return 1;
1438 : :
1439 : 0 : return slowfn(lock);
1440 : : }
1441 : :
1442 : : /*
1443 : : * Performs the wakeup of the the top-waiter and re-enables preemption.
1444 : : */
1445 : 0 : void rt_mutex_postunlock(struct wake_q_head *wake_q)
1446 : : {
1447 : 0 : wake_up_q(wake_q);
1448 : :
1449 : : /* Pairs with preempt_disable() in rt_mutex_slowunlock() */
1450 : 0 : preempt_enable();
1451 : 0 : }
1452 : :
1453 : : static inline void
1454 : 0 : rt_mutex_fastunlock(struct rt_mutex *lock,
1455 : : bool (*slowfn)(struct rt_mutex *lock,
1456 : : struct wake_q_head *wqh))
1457 : : {
1458 : 0 : DEFINE_WAKE_Q(wake_q);
1459 : :
1460 [ # # ]: 0 : if (likely(rt_mutex_cmpxchg_release(lock, current, NULL)))
1461 : 0 : return;
1462 : :
1463 [ # # ]: 0 : 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 : 0 : might_sleep();
1470 : :
1471 : : mutex_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
1472 : 0 : 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 : 0 : void __sched rt_mutex_lock(struct rt_mutex *lock)
1496 : : {
1497 : : __rt_mutex_lock(lock, 0);
1498 : 0 : }
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 : 0 : int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock)
1512 : : {
1513 : : int ret;
1514 : :
1515 : 0 : might_sleep();
1516 : :
1517 : : mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1518 : 0 : ret = rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE, rt_mutex_slowlock);
1519 : : if (ret)
1520 : : mutex_release(&lock->dep_map, 1, _RET_IP_);
1521 : :
1522 : 0 : return ret;
1523 : : }
1524 : : EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
1525 : :
1526 : : /*
1527 : : * Futex variant, must not use fastpath.
1528 : : */
1529 : 0 : int __sched rt_mutex_futex_trylock(struct rt_mutex *lock)
1530 : : {
1531 : 0 : return rt_mutex_slowtrylock(lock);
1532 : : }
1533 : :
1534 : 0 : int __sched __rt_mutex_futex_trylock(struct rt_mutex *lock)
1535 : : {
1536 : 0 : 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 : 0 : rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout)
1554 : : {
1555 : : int ret;
1556 : :
1557 : 0 : might_sleep();
1558 : :
1559 : : mutex_acquire(&lock->dep_map, 0, 0, _RET_IP_);
1560 : 0 : 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 : 0 : 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 : 0 : int __sched rt_mutex_trylock(struct rt_mutex *lock)
1582 : : {
1583 : : int ret;
1584 : :
1585 [ # # # # : 0 : if (WARN_ON_ONCE(in_irq() || in_nmi() || in_serving_softirq()))
# # # # #
# # # ]
1586 : : return 0;
1587 : :
1588 : 0 : ret = rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
1589 : : if (ret)
1590 : : mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
1591 : :
1592 : 0 : 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 : 0 : void __sched rt_mutex_unlock(struct rt_mutex *lock)
1602 : : {
1603 : : mutex_release(&lock->dep_map, 1, _RET_IP_);
1604 : 0 : rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
1605 : 0 : }
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 : 0 : 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 [ # # # # ]: 0 : if (!rt_mutex_has_waiters(lock)) {
1620 : 0 : lock->owner = NULL;
1621 : 0 : 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 : 0 : mark_wakeup_next_waiter(wake_q, lock);
1631 : :
1632 : 0 : return true; /* call postunlock() */
1633 : : }
1634 : :
1635 : 0 : void __sched rt_mutex_futex_unlock(struct rt_mutex *lock)
1636 : : {
1637 : 0 : DEFINE_WAKE_Q(wake_q);
1638 : : unsigned long flags;
1639 : : bool postunlock;
1640 : :
1641 : 0 : raw_spin_lock_irqsave(&lock->wait_lock, flags);
1642 : : postunlock = __rt_mutex_futex_unlock(lock, &wake_q);
1643 : 0 : raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1644 : :
1645 [ # # ]: 0 : if (postunlock)
1646 : : rt_mutex_postunlock(&wake_q);
1647 : 0 : }
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 : 0 : void rt_mutex_destroy(struct rt_mutex *lock)
1658 : : {
1659 [ # # ]: 0 : WARN_ON(rt_mutex_is_locked(lock));
1660 : : #ifdef CONFIG_DEBUG_RT_MUTEXES
1661 : : lock->magic = NULL;
1662 : : #endif
1663 : 0 : }
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 : 0 : void __rt_mutex_init(struct rt_mutex *lock, const char *name,
1676 : : struct lock_class_key *key)
1677 : : {
1678 : 0 : lock->owner = NULL;
1679 : 0 : raw_spin_lock_init(&lock->wait_lock);
1680 : 0 : lock->waiters = RB_ROOT_CACHED;
1681 : :
1682 : : if (name && key)
1683 : : debug_rt_mutex_init(lock, name, key);
1684 : 0 : }
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 : 0 : 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 : 0 : }
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 : 0 : 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 : 0 : }
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 : 0 : 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 [ # # ]: 0 : if (try_to_take_rt_mutex(lock, task, NULL))
1756 : : return 1;
1757 : :
1758 : : /* We enforce deadlock detection for futexes */
1759 : 0 : ret = task_blocks_on_rt_mutex(lock, waiter, task,
1760 : : RT_MUTEX_FULL_CHAINWALK);
1761 : :
1762 [ # # # # ]: 0 : 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 : 0 : 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 : 0 : 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 : 0 : raw_spin_lock_irq(&lock->wait_lock);
1803 : 0 : ret = __rt_mutex_start_proxy_lock(lock, waiter, task);
1804 [ # # ]: 0 : if (unlikely(ret))
1805 : 0 : remove_waiter(lock, waiter);
1806 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
1807 : :
1808 : 0 : 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 : 0 : struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1824 : : {
1825 [ # # ]: 0 : if (!rt_mutex_has_waiters(lock))
1826 : : return NULL;
1827 : :
1828 : 0 : 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 : 0 : 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 : 0 : raw_spin_lock_irq(&lock->wait_lock);
1855 : : /* sleep on the mutex */
1856 : 0 : set_current_state(TASK_INTERRUPTIBLE);
1857 : 0 : 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 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
1864 : :
1865 : 0 : 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 : 0 : bool rt_mutex_cleanup_proxy_lock(struct rt_mutex *lock,
1889 : : struct rt_mutex_waiter *waiter)
1890 : : {
1891 : : bool cleanup = false;
1892 : :
1893 : 0 : 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 : 0 : 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 [ # # ]: 0 : if (rt_mutex_owner(lock) != current) {
1911 : 0 : 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 : 0 : raw_spin_unlock_irq(&lock->wait_lock);
1921 : :
1922 : 0 : return cleanup;
1923 : : }
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