Branch data Line data Source code
1 : : /*
2 : : * RT-Mutexes: simple blocking mutual exclusion locks with PI support
3 : : *
4 : : * started by Ingo Molnar and Thomas Gleixner.
5 : : *
6 : : * Copyright (C) 2004-2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
7 : : * Copyright (C) 2005-2006 Timesys Corp., Thomas Gleixner <tglx@timesys.com>
8 : : * Copyright (C) 2005 Kihon Technologies Inc., Steven Rostedt
9 : : * Copyright (C) 2006 Esben Nielsen
10 : : *
11 : : * See Documentation/rt-mutex-design.txt for details.
12 : : */
13 : : #include <linux/spinlock.h>
14 : : #include <linux/export.h>
15 : : #include <linux/sched.h>
16 : : #include <linux/sched/rt.h>
17 : : #include <linux/sched/deadline.h>
18 : : #include <linux/timer.h>
19 : :
20 : : #include "rtmutex_common.h"
21 : :
22 : : /*
23 : : * lock->owner state tracking:
24 : : *
25 : : * lock->owner holds the task_struct pointer of the owner. Bit 0
26 : : * is used to keep track of the "lock has waiters" state.
27 : : *
28 : : * owner bit0
29 : : * NULL 0 lock is free (fast acquire possible)
30 : : * NULL 1 lock is free and has waiters and the top waiter
31 : : * is going to take the lock*
32 : : * taskpointer 0 lock is held (fast release possible)
33 : : * taskpointer 1 lock is held and has waiters**
34 : : *
35 : : * The fast atomic compare exchange based acquire and release is only
36 : : * possible when bit 0 of lock->owner is 0.
37 : : *
38 : : * (*) It also can be a transitional state when grabbing the lock
39 : : * with ->wait_lock is held. To prevent any fast path cmpxchg to the lock,
40 : : * we need to set the bit0 before looking at the lock, and the owner may be
41 : : * NULL in this small time, hence this can be a transitional state.
42 : : *
43 : : * (**) There is a small time when bit 0 is set but there are no
44 : : * waiters. This can happen when grabbing the lock in the slow path.
45 : : * To prevent a cmpxchg of the owner releasing the lock, we need to
46 : : * set this bit before looking at the lock.
47 : : */
48 : :
49 : : static void
50 : 0 : rt_mutex_set_owner(struct rt_mutex *lock, struct task_struct *owner)
51 : : {
52 : 0 : unsigned long val = (unsigned long)owner;
53 : :
54 [ # # ][ # # ]: 0 : if (rt_mutex_has_waiters(lock))
[ # # ]
55 : 0 : val |= RT_MUTEX_HAS_WAITERS;
56 : :
57 : 0 : lock->owner = (struct task_struct *)val;
58 : : }
59 : :
60 : : static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
61 : : {
62 : 0 : lock->owner = (struct task_struct *)
63 : 0 : ((unsigned long)lock->owner & ~RT_MUTEX_HAS_WAITERS);
64 : : }
65 : :
66 : 0 : static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
67 : : {
68 [ # # ][ # # ]: 0 : if (!rt_mutex_has_waiters(lock))
[ # # ]
69 : : clear_rt_mutex_waiters(lock);
70 : 0 : }
71 : :
72 : : /*
73 : : * We can speed up the acquire/release, if the architecture
74 : : * supports cmpxchg and if there's no debugging state to be set up
75 : : */
76 : : #if defined(__HAVE_ARCH_CMPXCHG) && !defined(CONFIG_DEBUG_RT_MUTEXES)
77 : : # define rt_mutex_cmpxchg(l,c,n) (cmpxchg(&l->owner, c, n) == c)
78 : : static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
79 : : {
80 : : unsigned long owner, *p = (unsigned long *) &lock->owner;
81 : :
82 : : do {
83 : : owner = *p;
84 : : } while (cmpxchg(p, owner, owner | RT_MUTEX_HAS_WAITERS) != owner);
85 : : }
86 : : #else
87 : : # define rt_mutex_cmpxchg(l,c,n) (0)
88 : : static inline void mark_rt_mutex_waiters(struct rt_mutex *lock)
89 : : {
90 : 0 : lock->owner = (struct task_struct *)
91 : 0 : ((unsigned long)lock->owner | RT_MUTEX_HAS_WAITERS);
92 : : }
93 : : #endif
94 : :
95 : : static inline int
96 : : rt_mutex_waiter_less(struct rt_mutex_waiter *left,
97 : : struct rt_mutex_waiter *right)
98 : : {
99 [ # # ][ # # ]: 0 : if (left->prio < right->prio)
100 : : return 1;
101 : :
102 : : /*
103 : : * If both waiters have dl_prio(), we check the deadlines of the
104 : : * associated tasks.
105 : : * If left waiter has a dl_prio(), and we didn't return 1 above,
106 : : * then right waiter has a dl_prio() too.
107 : : */
108 [ # # ][ # # ]: 0 : if (dl_prio(left->prio))
109 : 0 : return (left->task->dl.deadline < right->task->dl.deadline);
110 : :
111 : : return 0;
112 : : }
113 : :
114 : : static void
115 : 0 : rt_mutex_enqueue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
116 : : {
117 : 0 : struct rb_node **link = &lock->waiters.rb_node;
118 : : struct rb_node *parent = NULL;
119 : 0 : struct rt_mutex_waiter *entry;
120 : : int leftmost = 1;
121 : :
122 [ # # ]: 0 : while (*link) {
123 : : parent = *link;
124 : : entry = rb_entry(parent, struct rt_mutex_waiter, tree_entry);
125 [ # # ]: 0 : if (rt_mutex_waiter_less(waiter, entry)) {
126 : 0 : link = &parent->rb_left;
127 : : } else {
128 : 0 : link = &parent->rb_right;
129 : : leftmost = 0;
130 : : }
131 : : }
132 : :
133 [ # # ]: 0 : if (leftmost)
134 : 0 : lock->waiters_leftmost = &waiter->tree_entry;
135 : :
136 : 0 : rb_link_node(&waiter->tree_entry, parent, link);
137 : 0 : rb_insert_color(&waiter->tree_entry, &lock->waiters);
138 : 0 : }
139 : :
140 : : static void
141 : 0 : rt_mutex_dequeue(struct rt_mutex *lock, struct rt_mutex_waiter *waiter)
142 : : {
143 [ # # ]: 0 : if (RB_EMPTY_NODE(&waiter->tree_entry))
144 : 0 : return;
145 : :
146 [ # # ]: 0 : if (lock->waiters_leftmost == &waiter->tree_entry)
147 : 0 : lock->waiters_leftmost = rb_next(&waiter->tree_entry);
148 : :
149 : 0 : rb_erase(&waiter->tree_entry, &lock->waiters);
150 : 0 : RB_CLEAR_NODE(&waiter->tree_entry);
151 : : }
152 : :
153 : : static void
154 : 0 : rt_mutex_enqueue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
155 : : {
156 : 0 : struct rb_node **link = &task->pi_waiters.rb_node;
157 : : struct rb_node *parent = NULL;
158 : 0 : struct rt_mutex_waiter *entry;
159 : : int leftmost = 1;
160 : :
161 [ # # ]: 0 : while (*link) {
162 : : parent = *link;
163 : : entry = rb_entry(parent, struct rt_mutex_waiter, pi_tree_entry);
164 [ # # ]: 0 : if (rt_mutex_waiter_less(waiter, entry)) {
165 : 0 : link = &parent->rb_left;
166 : : } else {
167 : 0 : link = &parent->rb_right;
168 : : leftmost = 0;
169 : : }
170 : : }
171 : :
172 [ # # ]: 0 : if (leftmost)
173 : 0 : task->pi_waiters_leftmost = &waiter->pi_tree_entry;
174 : :
175 : 0 : rb_link_node(&waiter->pi_tree_entry, parent, link);
176 : 0 : rb_insert_color(&waiter->pi_tree_entry, &task->pi_waiters);
177 : 0 : }
178 : :
179 : : static void
180 : 0 : rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
181 : : {
182 [ # # ]: 0 : if (RB_EMPTY_NODE(&waiter->pi_tree_entry))
183 : 0 : return;
184 : :
185 [ # # ]: 0 : if (task->pi_waiters_leftmost == &waiter->pi_tree_entry)
186 : 0 : task->pi_waiters_leftmost = rb_next(&waiter->pi_tree_entry);
187 : :
188 : 0 : rb_erase(&waiter->pi_tree_entry, &task->pi_waiters);
189 : 0 : RB_CLEAR_NODE(&waiter->pi_tree_entry);
190 : : }
191 : :
192 : : /*
193 : : * Calculate task priority from the waiter tree priority
194 : : *
195 : : * Return task->normal_prio when the waiter tree is empty or when
196 : : * the waiter is not allowed to do priority boosting
197 : : */
198 : 0 : int rt_mutex_getprio(struct task_struct *task)
199 : : {
200 [ # # ][ + - ]: 66 : if (likely(!task_has_pi_waiters(task)))
201 : 66 : return task->normal_prio;
202 : :
203 : 0 : return min(task_top_pi_waiter(task)->prio,
204 : : task->normal_prio);
205 : : }
206 : :
207 : 0 : struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
208 : : {
209 [ # # ]: 0 : if (likely(!task_has_pi_waiters(task)))
210 : : return NULL;
211 : :
212 : 0 : return task_top_pi_waiter(task)->task;
213 : : }
214 : :
215 : : /*
216 : : * Adjust the priority of a task, after its pi_waiters got modified.
217 : : *
218 : : * This can be both boosting and unboosting. task->pi_lock must be held.
219 : : */
220 : 0 : static void __rt_mutex_adjust_prio(struct task_struct *task)
221 : : {
222 : : int prio = rt_mutex_getprio(task);
223 : :
224 [ # # ][ # # ]: 0 : if (task->prio != prio || dl_prio(prio))
225 : 0 : rt_mutex_setprio(task, prio);
226 : 0 : }
227 : :
228 : : /*
229 : : * Adjust task priority (undo boosting). Called from the exit path of
230 : : * rt_mutex_slowunlock() and rt_mutex_slowlock().
231 : : *
232 : : * (Note: We do this outside of the protection of lock->wait_lock to
233 : : * allow the lock to be taken while or before we readjust the priority
234 : : * of task. We do not use the spin_xx_mutex() variants here as we are
235 : : * outside of the debug path.)
236 : : */
237 : 0 : static void rt_mutex_adjust_prio(struct task_struct *task)
238 : : {
239 : : unsigned long flags;
240 : :
241 : 0 : raw_spin_lock_irqsave(&task->pi_lock, flags);
242 : 0 : __rt_mutex_adjust_prio(task);
243 : 0 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
244 : 0 : }
245 : :
246 : : /*
247 : : * Max number of times we'll walk the boosting chain:
248 : : */
249 : : int max_lock_depth = 1024;
250 : :
251 : : /*
252 : : * Adjust the priority chain. Also used for deadlock detection.
253 : : * Decreases task's usage by one - may thus free the task.
254 : : *
255 : : * @task: the task owning the mutex (owner) for which a chain walk is probably
256 : : * needed
257 : : * @deadlock_detect: do we have to carry out deadlock detection?
258 : : * @orig_lock: the mutex (can be NULL if we are walking the chain to recheck
259 : : * things for a task that has just got its priority adjusted, and
260 : : * is waiting on a mutex)
261 : : * @orig_waiter: rt_mutex_waiter struct for the task that has just donated
262 : : * its priority to the mutex owner (can be NULL in the case
263 : : * depicted above or if the top waiter is gone away and we are
264 : : * actually deboosting the owner)
265 : : * @top_task: the current top waiter
266 : : *
267 : : * Returns 0 or -EDEADLK.
268 : : */
269 : 0 : static int rt_mutex_adjust_prio_chain(struct task_struct *task,
270 : : int deadlock_detect,
271 : 0 : struct rt_mutex *orig_lock,
272 : : struct rt_mutex_waiter *orig_waiter,
273 : : struct task_struct *top_task)
274 : : {
275 : 0 : struct rt_mutex *lock;
276 : : struct rt_mutex_waiter *waiter, *top_waiter = orig_waiter;
277 : : int detect_deadlock, ret = 0, depth = 0;
278 : : unsigned long flags;
279 : :
280 : : detect_deadlock = debug_rt_mutex_detect_deadlock(orig_waiter,
281 : : deadlock_detect);
282 : :
283 : : /*
284 : : * The (de)boosting is a step by step approach with a lot of
285 : : * pitfalls. We want this to be preemptible and we want hold a
286 : : * maximum of two locks per step. So we have to check
287 : : * carefully whether things change under us.
288 : : */
289 : : again:
290 [ # # ]: 0 : if (++depth > max_lock_depth) {
291 : : static int prev_max;
292 : :
293 : : /*
294 : : * Print this only once. If the admin changes the limit,
295 : : * print a new message when reaching the limit again.
296 : : */
297 [ # # ]: 0 : if (prev_max != max_lock_depth) {
298 : 0 : prev_max = max_lock_depth;
299 : 0 : printk(KERN_WARNING "Maximum lock depth %d reached "
300 : : "task: %s (%d)\n", max_lock_depth,
301 : 0 : top_task->comm, task_pid_nr(top_task));
302 : : }
303 : : put_task_struct(task);
304 : :
305 [ # # ]: 0 : return deadlock_detect ? -EDEADLK : 0;
306 : : }
307 : : retry:
308 : : /*
309 : : * Task can not go away as we did a get_task() before !
310 : : */
311 : 0 : raw_spin_lock_irqsave(&task->pi_lock, flags);
312 : :
313 : 0 : waiter = task->pi_blocked_on;
314 : : /*
315 : : * Check whether the end of the boosting chain has been
316 : : * reached or the state of the chain has changed while we
317 : : * dropped the locks.
318 : : */
319 [ # # ]: 0 : if (!waiter)
320 : : goto out_unlock_pi;
321 : :
322 : : /*
323 : : * Check the orig_waiter state. After we dropped the locks,
324 : : * the previous owner of the lock might have released the lock.
325 : : */
326 [ # # ][ # # ]: 0 : if (orig_waiter && !rt_mutex_owner(orig_lock))
327 : : goto out_unlock_pi;
328 : :
329 : : /*
330 : : * Drop out, when the task has no waiters. Note,
331 : : * top_waiter can be NULL, when we are in the deboosting
332 : : * mode!
333 : : */
334 [ # # ][ # # ]: 0 : if (top_waiter && (!task_has_pi_waiters(task) ||
[ # # ]
335 : 0 : top_waiter != task_top_pi_waiter(task)))
336 : : goto out_unlock_pi;
337 : :
338 : : /*
339 : : * When deadlock detection is off then we check, if further
340 : : * priority adjustment is necessary.
341 : : */
342 [ # # ][ # # ]: 0 : if (!detect_deadlock && waiter->prio == task->prio)
343 : : goto out_unlock_pi;
344 : :
345 : 0 : lock = waiter->lock;
346 [ # # ]: 0 : if (!raw_spin_trylock(&lock->wait_lock)) {
347 : 0 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
348 : 0 : cpu_relax();
349 : 0 : goto retry;
350 : : }
351 : :
352 : : /* Deadlock detection */
353 [ # # ][ # # ]: 0 : if (lock == orig_lock || rt_mutex_owner(lock) == top_task) {
354 : : debug_rt_mutex_deadlock(deadlock_detect, orig_waiter, lock);
355 : : raw_spin_unlock(&lock->wait_lock);
356 [ # # ]: 0 : ret = deadlock_detect ? -EDEADLK : 0;
357 : 0 : goto out_unlock_pi;
358 : : }
359 : :
360 : : top_waiter = rt_mutex_top_waiter(lock);
361 : :
362 : : /* Requeue the waiter */
363 : 0 : rt_mutex_dequeue(lock, waiter);
364 : 0 : waiter->prio = task->prio;
365 : 0 : rt_mutex_enqueue(lock, waiter);
366 : :
367 : : /* Release the task */
368 : 0 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
369 [ # # ]: 0 : if (!rt_mutex_owner(lock)) {
370 : : /*
371 : : * If the requeue above changed the top waiter, then we need
372 : : * to wake the new top waiter up to try to get the lock.
373 : : */
374 : :
375 [ # # ]: 0 : if (top_waiter != rt_mutex_top_waiter(lock))
376 : 0 : wake_up_process(rt_mutex_top_waiter(lock)->task);
377 : : raw_spin_unlock(&lock->wait_lock);
378 : : goto out_put_task;
379 : : }
380 : : put_task_struct(task);
381 : :
382 : : /* Grab the next task */
383 : : task = rt_mutex_owner(lock);
384 : 0 : get_task_struct(task);
385 : 0 : raw_spin_lock_irqsave(&task->pi_lock, flags);
386 : :
387 [ # # ]: 0 : if (waiter == rt_mutex_top_waiter(lock)) {
388 : : /* Boost the owner */
389 : 0 : rt_mutex_dequeue_pi(task, top_waiter);
390 : 0 : rt_mutex_enqueue_pi(task, waiter);
391 : 0 : __rt_mutex_adjust_prio(task);
392 : :
393 [ # # ]: 0 : } else if (top_waiter == waiter) {
394 : : /* Deboost the owner */
395 : 0 : rt_mutex_dequeue_pi(task, waiter);
396 : : waiter = rt_mutex_top_waiter(lock);
397 : 0 : rt_mutex_enqueue_pi(task, waiter);
398 : 0 : __rt_mutex_adjust_prio(task);
399 : : }
400 : :
401 : 0 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
402 : :
403 : : top_waiter = rt_mutex_top_waiter(lock);
404 : : raw_spin_unlock(&lock->wait_lock);
405 : :
406 [ # # ]: 0 : if (!detect_deadlock && waiter != top_waiter)
407 : : goto out_put_task;
408 : :
409 : : goto again;
410 : :
411 : : out_unlock_pi:
412 : 0 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
413 : : out_put_task:
414 : : put_task_struct(task);
415 : :
416 : 0 : return ret;
417 : : }
418 : :
419 : : /*
420 : : * Try to take an rt-mutex
421 : : *
422 : : * Must be called with lock->wait_lock held.
423 : : *
424 : : * @lock: the lock to be acquired.
425 : : * @task: the task which wants to acquire the lock
426 : : * @waiter: the waiter that is queued to the lock's wait list. (could be NULL)
427 : : */
428 : 0 : static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
429 : : struct rt_mutex_waiter *waiter)
430 : : {
431 : : /*
432 : : * We have to be careful here if the atomic speedups are
433 : : * enabled, such that, when
434 : : * - no other waiter is on the lock
435 : : * - the lock has been released since we did the cmpxchg
436 : : * the lock can be released or taken while we are doing the
437 : : * checks and marking the lock with RT_MUTEX_HAS_WAITERS.
438 : : *
439 : : * The atomic acquire/release aware variant of
440 : : * mark_rt_mutex_waiters uses a cmpxchg loop. After setting
441 : : * the WAITERS bit, the atomic release / acquire can not
442 : : * happen anymore and lock->wait_lock protects us from the
443 : : * non-atomic case.
444 : : *
445 : : * Note, that this might set lock->owner =
446 : : * RT_MUTEX_HAS_WAITERS in the case the lock is not contended
447 : : * any more. This is fixed up when we take the ownership.
448 : : * This is the transitional state explained at the top of this file.
449 : : */
450 : : mark_rt_mutex_waiters(lock);
451 : :
452 [ # # ]: 0 : if (rt_mutex_owner(lock))
453 : : return 0;
454 : :
455 : : /*
456 : : * It will get the lock because of one of these conditions:
457 : : * 1) there is no waiter
458 : : * 2) higher priority than waiters
459 : : * 3) it is top waiter
460 : : */
461 [ # # ]: 0 : if (rt_mutex_has_waiters(lock)) {
462 [ # # ]: 0 : if (task->prio >= rt_mutex_top_waiter(lock)->prio) {
463 [ # # ][ # # ]: 0 : if (!waiter || waiter != rt_mutex_top_waiter(lock))
464 : : return 0;
465 : : }
466 : : }
467 : :
468 [ # # ][ # # ]: 0 : if (waiter || rt_mutex_has_waiters(lock)) {
469 : : unsigned long flags;
470 : : struct rt_mutex_waiter *top;
471 : :
472 : 0 : raw_spin_lock_irqsave(&task->pi_lock, flags);
473 : :
474 : : /* remove the queued waiter. */
475 [ # # ]: 0 : if (waiter) {
476 : 0 : rt_mutex_dequeue(lock, waiter);
477 : 0 : task->pi_blocked_on = NULL;
478 : : }
479 : :
480 : : /*
481 : : * We have to enqueue the top waiter(if it exists) into
482 : : * task->pi_waiters list.
483 : : */
484 [ # # ]: 0 : if (rt_mutex_has_waiters(lock)) {
485 : : top = rt_mutex_top_waiter(lock);
486 : 0 : rt_mutex_enqueue_pi(task, top);
487 : : }
488 : 0 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
489 : : }
490 : :
491 : : /* We got the lock. */
492 : : debug_rt_mutex_lock(lock);
493 : :
494 : : rt_mutex_set_owner(lock, task);
495 : :
496 : : rt_mutex_deadlock_account_lock(lock, task);
497 : :
498 : 0 : return 1;
499 : : }
500 : :
501 : : /*
502 : : * Task blocks on lock.
503 : : *
504 : : * Prepare waiter and propagate pi chain
505 : : *
506 : : * This must be called with lock->wait_lock held.
507 : : */
508 : 0 : static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
509 : : struct rt_mutex_waiter *waiter,
510 : : struct task_struct *task,
511 : : int detect_deadlock)
512 : : {
513 : : struct task_struct *owner = rt_mutex_owner(lock);
514 : : struct rt_mutex_waiter *top_waiter = waiter;
515 : : unsigned long flags;
516 : : int chain_walk = 0, res;
517 : :
518 : 0 : raw_spin_lock_irqsave(&task->pi_lock, flags);
519 : 0 : __rt_mutex_adjust_prio(task);
520 : 0 : waiter->task = task;
521 : 0 : waiter->lock = lock;
522 : 0 : waiter->prio = task->prio;
523 : :
524 : : /* Get the top priority waiter on the lock */
525 [ # # ]: 0 : if (rt_mutex_has_waiters(lock))
526 : : top_waiter = rt_mutex_top_waiter(lock);
527 : 0 : rt_mutex_enqueue(lock, waiter);
528 : :
529 : 0 : task->pi_blocked_on = waiter;
530 : :
531 : 0 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
532 : :
533 [ # # ]: 0 : if (!owner)
534 : : return 0;
535 : :
536 [ # # ]: 0 : if (waiter == rt_mutex_top_waiter(lock)) {
537 : 0 : raw_spin_lock_irqsave(&owner->pi_lock, flags);
538 : 0 : rt_mutex_dequeue_pi(owner, top_waiter);
539 : 0 : rt_mutex_enqueue_pi(owner, waiter);
540 : :
541 : 0 : __rt_mutex_adjust_prio(owner);
542 [ # # ]: 0 : if (owner->pi_blocked_on)
543 : : chain_walk = 1;
544 : 0 : raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
545 : : }
546 [ # # ]: 0 : else if (debug_rt_mutex_detect_deadlock(waiter, detect_deadlock))
547 : : chain_walk = 1;
548 : :
549 [ # # ]: 0 : if (!chain_walk)
550 : : return 0;
551 : :
552 : : /*
553 : : * The owner can't disappear while holding a lock,
554 : : * so the owner struct is protected by wait_lock.
555 : : * Gets dropped in rt_mutex_adjust_prio_chain()!
556 : : */
557 : 0 : get_task_struct(owner);
558 : :
559 : : raw_spin_unlock(&lock->wait_lock);
560 : :
561 : 0 : res = rt_mutex_adjust_prio_chain(owner, detect_deadlock, lock, waiter,
562 : : task);
563 : :
564 : 0 : raw_spin_lock(&lock->wait_lock);
565 : :
566 : 0 : return res;
567 : : }
568 : :
569 : : /*
570 : : * Wake up the next waiter on the lock.
571 : : *
572 : : * Remove the top waiter from the current tasks waiter list and wake it up.
573 : : *
574 : : * Called with lock->wait_lock held.
575 : : */
576 : 0 : static void wakeup_next_waiter(struct rt_mutex *lock)
577 : : {
578 : : struct rt_mutex_waiter *waiter;
579 : : unsigned long flags;
580 : :
581 : 0 : raw_spin_lock_irqsave(¤t->pi_lock, flags);
582 : :
583 : : waiter = rt_mutex_top_waiter(lock);
584 : :
585 : : /*
586 : : * Remove it from current->pi_waiters. We do not adjust a
587 : : * possible priority boost right now. We execute wakeup in the
588 : : * boosted mode and go back to normal after releasing
589 : : * lock->wait_lock.
590 : : */
591 : 0 : rt_mutex_dequeue_pi(current, waiter);
592 : :
593 : : rt_mutex_set_owner(lock, NULL);
594 : :
595 : 0 : raw_spin_unlock_irqrestore(¤t->pi_lock, flags);
596 : :
597 : 0 : wake_up_process(waiter->task);
598 : 0 : }
599 : :
600 : : /*
601 : : * Remove a waiter from a lock and give up
602 : : *
603 : : * Must be called with lock->wait_lock held and
604 : : * have just failed to try_to_take_rt_mutex().
605 : : */
606 : 0 : static void remove_waiter(struct rt_mutex *lock,
607 : : struct rt_mutex_waiter *waiter)
608 : : {
609 : : int first = (waiter == rt_mutex_top_waiter(lock));
610 : : struct task_struct *owner = rt_mutex_owner(lock);
611 : : unsigned long flags;
612 : : int chain_walk = 0;
613 : :
614 : 0 : raw_spin_lock_irqsave(¤t->pi_lock, flags);
615 : 0 : rt_mutex_dequeue(lock, waiter);
616 : 0 : current->pi_blocked_on = NULL;
617 : 0 : raw_spin_unlock_irqrestore(¤t->pi_lock, flags);
618 : :
619 [ # # ]: 0 : if (!owner)
620 : : return;
621 : :
622 [ # # ]: 0 : if (first) {
623 : :
624 : 0 : raw_spin_lock_irqsave(&owner->pi_lock, flags);
625 : :
626 : 0 : rt_mutex_dequeue_pi(owner, waiter);
627 : :
628 [ # # ]: 0 : if (rt_mutex_has_waiters(lock)) {
629 : : struct rt_mutex_waiter *next;
630 : :
631 : : next = rt_mutex_top_waiter(lock);
632 : 0 : rt_mutex_enqueue_pi(owner, next);
633 : : }
634 : 0 : __rt_mutex_adjust_prio(owner);
635 : :
636 [ # # ]: 0 : if (owner->pi_blocked_on)
637 : : chain_walk = 1;
638 : :
639 : 0 : raw_spin_unlock_irqrestore(&owner->pi_lock, flags);
640 : : }
641 : :
642 [ # # ]: 0 : if (!chain_walk)
643 : : return;
644 : :
645 : : /* gets dropped in rt_mutex_adjust_prio_chain()! */
646 : 0 : get_task_struct(owner);
647 : :
648 : : raw_spin_unlock(&lock->wait_lock);
649 : :
650 : 0 : rt_mutex_adjust_prio_chain(owner, 0, lock, NULL, current);
651 : :
652 : 0 : raw_spin_lock(&lock->wait_lock);
653 : : }
654 : :
655 : : /*
656 : : * Recheck the pi chain, in case we got a priority setting
657 : : *
658 : : * Called from sched_setscheduler
659 : : */
660 : 0 : void rt_mutex_adjust_pi(struct task_struct *task)
661 : : {
662 : : struct rt_mutex_waiter *waiter;
663 : : unsigned long flags;
664 : :
665 : 66 : raw_spin_lock_irqsave(&task->pi_lock, flags);
666 : :
667 : 66 : waiter = task->pi_blocked_on;
668 [ - + ][ # # ]: 66 : if (!waiter || (waiter->prio == task->prio &&
[ # # ]
669 : : !dl_prio(task->prio))) {
670 : 66 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
671 : 66 : return;
672 : : }
673 : :
674 : 0 : raw_spin_unlock_irqrestore(&task->pi_lock, flags);
675 : :
676 : : /* gets dropped in rt_mutex_adjust_prio_chain()! */
677 : 0 : get_task_struct(task);
678 : 0 : rt_mutex_adjust_prio_chain(task, 0, NULL, NULL, task);
679 : : }
680 : :
681 : : /**
682 : : * __rt_mutex_slowlock() - Perform the wait-wake-try-to-take loop
683 : : * @lock: the rt_mutex to take
684 : : * @state: the state the task should block in (TASK_INTERRUPTIBLE
685 : : * or TASK_UNINTERRUPTIBLE)
686 : : * @timeout: the pre-initialized and started timer, or NULL for none
687 : : * @waiter: the pre-initialized rt_mutex_waiter
688 : : *
689 : : * lock->wait_lock must be held by the caller.
690 : : */
691 : : static int __sched
692 : 0 : __rt_mutex_slowlock(struct rt_mutex *lock, int state,
693 : : struct hrtimer_sleeper *timeout,
694 : : struct rt_mutex_waiter *waiter)
695 : : {
696 : : int ret = 0;
697 : :
698 : : for (;;) {
699 : : /* Try to acquire the lock: */
700 [ # # ]: 0 : if (try_to_take_rt_mutex(lock, current, waiter))
701 : : break;
702 : :
703 : : /*
704 : : * TASK_INTERRUPTIBLE checks for signals and
705 : : * timeout. Ignored otherwise.
706 : : */
707 [ # # ]: 0 : if (unlikely(state == TASK_INTERRUPTIBLE)) {
708 : : /* Signal pending? */
709 [ # # ]: 0 : if (signal_pending(current))
710 : : ret = -EINTR;
711 [ # # ][ # # ]: 0 : if (timeout && !timeout->task)
712 : : ret = -ETIMEDOUT;
713 [ # # ]: 0 : if (ret)
714 : : break;
715 : : }
716 : :
717 : : raw_spin_unlock(&lock->wait_lock);
718 : :
719 : : debug_rt_mutex_print_deadlock(waiter);
720 : :
721 : 0 : schedule_rt_mutex(lock);
722 : :
723 : 0 : raw_spin_lock(&lock->wait_lock);
724 : 0 : set_current_state(state);
725 : 0 : }
726 : :
727 : 0 : return ret;
728 : : }
729 : :
730 : : /*
731 : : * Slow path lock function:
732 : : */
733 : : static int __sched
734 : 0 : rt_mutex_slowlock(struct rt_mutex *lock, int state,
735 : : struct hrtimer_sleeper *timeout,
736 : : int detect_deadlock)
737 : : {
738 : : struct rt_mutex_waiter waiter;
739 : : int ret = 0;
740 : :
741 : : debug_rt_mutex_init_waiter(&waiter);
742 : 0 : RB_CLEAR_NODE(&waiter.pi_tree_entry);
743 : 0 : RB_CLEAR_NODE(&waiter.tree_entry);
744 : :
745 : 0 : raw_spin_lock(&lock->wait_lock);
746 : :
747 : : /* Try to acquire the lock again: */
748 [ # # ]: 0 : if (try_to_take_rt_mutex(lock, current, NULL)) {
749 : : raw_spin_unlock(&lock->wait_lock);
750 : 0 : return 0;
751 : : }
752 : :
753 : 0 : set_current_state(state);
754 : :
755 : : /* Setup the timer, when timeout != NULL */
756 [ # # ]: 0 : if (unlikely(timeout)) {
757 : 0 : hrtimer_start_expires(&timeout->timer, HRTIMER_MODE_ABS);
758 [ # # ]: 0 : if (!hrtimer_active(&timeout->timer))
759 : 0 : timeout->task = NULL;
760 : : }
761 : :
762 : 0 : ret = task_blocks_on_rt_mutex(lock, &waiter, current, detect_deadlock);
763 : :
764 [ # # ]: 0 : if (likely(!ret))
765 : 0 : ret = __rt_mutex_slowlock(lock, state, timeout, &waiter);
766 : :
767 : 0 : set_current_state(TASK_RUNNING);
768 : :
769 [ # # ]: 0 : if (unlikely(ret))
770 : 0 : remove_waiter(lock, &waiter);
771 : :
772 : : /*
773 : : * try_to_take_rt_mutex() sets the waiter bit
774 : : * unconditionally. We might have to fix that up.
775 : : */
776 : : fixup_rt_mutex_waiters(lock);
777 : :
778 : : raw_spin_unlock(&lock->wait_lock);
779 : :
780 : : /* Remove pending timer: */
781 [ # # ]: 0 : if (unlikely(timeout))
782 : 0 : hrtimer_cancel(&timeout->timer);
783 : :
784 : : debug_rt_mutex_free_waiter(&waiter);
785 : :
786 : 0 : return ret;
787 : : }
788 : :
789 : : /*
790 : : * Slow path try-lock function:
791 : : */
792 : : static inline int
793 : 0 : rt_mutex_slowtrylock(struct rt_mutex *lock)
794 : : {
795 : : int ret = 0;
796 : :
797 : 0 : raw_spin_lock(&lock->wait_lock);
798 : :
799 [ # # ]: 0 : if (likely(rt_mutex_owner(lock) != current)) {
800 : :
801 : 0 : ret = try_to_take_rt_mutex(lock, current, NULL);
802 : : /*
803 : : * try_to_take_rt_mutex() sets the lock waiters
804 : : * bit unconditionally. Clean this up.
805 : : */
806 : 0 : fixup_rt_mutex_waiters(lock);
807 : : }
808 : :
809 : : raw_spin_unlock(&lock->wait_lock);
810 : :
811 : 0 : return ret;
812 : : }
813 : :
814 : : /*
815 : : * Slow path to release a rt-mutex:
816 : : */
817 : : static void __sched
818 : 0 : rt_mutex_slowunlock(struct rt_mutex *lock)
819 : : {
820 : 0 : raw_spin_lock(&lock->wait_lock);
821 : :
822 : : debug_rt_mutex_unlock(lock);
823 : :
824 : : rt_mutex_deadlock_account_unlock(current);
825 : :
826 [ # # ]: 0 : if (!rt_mutex_has_waiters(lock)) {
827 : 0 : lock->owner = NULL;
828 : : raw_spin_unlock(&lock->wait_lock);
829 : 0 : return;
830 : : }
831 : :
832 : 0 : wakeup_next_waiter(lock);
833 : :
834 : : raw_spin_unlock(&lock->wait_lock);
835 : :
836 : : /* Undo pi boosting if necessary: */
837 : 0 : rt_mutex_adjust_prio(current);
838 : : }
839 : :
840 : : /*
841 : : * debug aware fast / slowpath lock,trylock,unlock
842 : : *
843 : : * The atomic acquire/release ops are compiled away, when either the
844 : : * architecture does not support cmpxchg or when debugging is enabled.
845 : : */
846 : : static inline int
847 : : rt_mutex_fastlock(struct rt_mutex *lock, int state,
848 : : int detect_deadlock,
849 : : int (*slowfn)(struct rt_mutex *lock, int state,
850 : : struct hrtimer_sleeper *timeout,
851 : : int detect_deadlock))
852 : : {
853 : : if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
854 : : rt_mutex_deadlock_account_lock(lock, current);
855 : : return 0;
856 : : } else
857 : 0 : return slowfn(lock, state, NULL, detect_deadlock);
858 : : }
859 : :
860 : : static inline int
861 : : rt_mutex_timed_fastlock(struct rt_mutex *lock, int state,
862 : : struct hrtimer_sleeper *timeout, int detect_deadlock,
863 : : int (*slowfn)(struct rt_mutex *lock, int state,
864 : : struct hrtimer_sleeper *timeout,
865 : : int detect_deadlock))
866 : : {
867 : : if (!detect_deadlock && likely(rt_mutex_cmpxchg(lock, NULL, current))) {
868 : : rt_mutex_deadlock_account_lock(lock, current);
869 : : return 0;
870 : : } else
871 : 0 : return slowfn(lock, state, timeout, detect_deadlock);
872 : : }
873 : :
874 : : static inline int
875 : : rt_mutex_fasttrylock(struct rt_mutex *lock,
876 : : int (*slowfn)(struct rt_mutex *lock))
877 : : {
878 : : if (likely(rt_mutex_cmpxchg(lock, NULL, current))) {
879 : : rt_mutex_deadlock_account_lock(lock, current);
880 : : return 1;
881 : : }
882 : 0 : return slowfn(lock);
883 : : }
884 : :
885 : : static inline void
886 : : rt_mutex_fastunlock(struct rt_mutex *lock,
887 : : void (*slowfn)(struct rt_mutex *lock))
888 : : {
889 : : if (likely(rt_mutex_cmpxchg(lock, current, NULL)))
890 : : rt_mutex_deadlock_account_unlock(current);
891 : : else
892 : 0 : slowfn(lock);
893 : : }
894 : :
895 : : /**
896 : : * rt_mutex_lock - lock a rt_mutex
897 : : *
898 : : * @lock: the rt_mutex to be locked
899 : : */
900 : 0 : void __sched rt_mutex_lock(struct rt_mutex *lock)
901 : : {
902 : : might_sleep();
903 : :
904 : : rt_mutex_fastlock(lock, TASK_UNINTERRUPTIBLE, 0, rt_mutex_slowlock);
905 : 0 : }
906 : : EXPORT_SYMBOL_GPL(rt_mutex_lock);
907 : :
908 : : /**
909 : : * rt_mutex_lock_interruptible - lock a rt_mutex interruptible
910 : : *
911 : : * @lock: the rt_mutex to be locked
912 : : * @detect_deadlock: deadlock detection on/off
913 : : *
914 : : * Returns:
915 : : * 0 on success
916 : : * -EINTR when interrupted by a signal
917 : : * -EDEADLK when the lock would deadlock (when deadlock detection is on)
918 : : */
919 : 0 : int __sched rt_mutex_lock_interruptible(struct rt_mutex *lock,
920 : : int detect_deadlock)
921 : : {
922 : : might_sleep();
923 : :
924 : 0 : return rt_mutex_fastlock(lock, TASK_INTERRUPTIBLE,
925 : : detect_deadlock, rt_mutex_slowlock);
926 : : }
927 : : EXPORT_SYMBOL_GPL(rt_mutex_lock_interruptible);
928 : :
929 : : /**
930 : : * rt_mutex_timed_lock - lock a rt_mutex interruptible
931 : : * the timeout structure is provided
932 : : * by the caller
933 : : *
934 : : * @lock: the rt_mutex to be locked
935 : : * @timeout: timeout structure or NULL (no timeout)
936 : : * @detect_deadlock: deadlock detection on/off
937 : : *
938 : : * Returns:
939 : : * 0 on success
940 : : * -EINTR when interrupted by a signal
941 : : * -ETIMEDOUT when the timeout expired
942 : : * -EDEADLK when the lock would deadlock (when deadlock detection is on)
943 : : */
944 : : int
945 : 0 : rt_mutex_timed_lock(struct rt_mutex *lock, struct hrtimer_sleeper *timeout,
946 : : int detect_deadlock)
947 : : {
948 : : might_sleep();
949 : :
950 : 0 : return rt_mutex_timed_fastlock(lock, TASK_INTERRUPTIBLE, timeout,
951 : : detect_deadlock, rt_mutex_slowlock);
952 : : }
953 : : EXPORT_SYMBOL_GPL(rt_mutex_timed_lock);
954 : :
955 : : /**
956 : : * rt_mutex_trylock - try to lock a rt_mutex
957 : : *
958 : : * @lock: the rt_mutex to be locked
959 : : *
960 : : * Returns 1 on success and 0 on contention
961 : : */
962 : 0 : int __sched rt_mutex_trylock(struct rt_mutex *lock)
963 : : {
964 : 0 : return rt_mutex_fasttrylock(lock, rt_mutex_slowtrylock);
965 : : }
966 : : EXPORT_SYMBOL_GPL(rt_mutex_trylock);
967 : :
968 : : /**
969 : : * rt_mutex_unlock - unlock a rt_mutex
970 : : *
971 : : * @lock: the rt_mutex to be unlocked
972 : : */
973 : 0 : void __sched rt_mutex_unlock(struct rt_mutex *lock)
974 : : {
975 : : rt_mutex_fastunlock(lock, rt_mutex_slowunlock);
976 : 0 : }
977 : : EXPORT_SYMBOL_GPL(rt_mutex_unlock);
978 : :
979 : : /**
980 : : * rt_mutex_destroy - mark a mutex unusable
981 : : * @lock: the mutex to be destroyed
982 : : *
983 : : * This function marks the mutex uninitialized, and any subsequent
984 : : * use of the mutex is forbidden. The mutex must not be locked when
985 : : * this function is called.
986 : : */
987 : 0 : void rt_mutex_destroy(struct rt_mutex *lock)
988 : : {
989 [ # # ]: 0 : WARN_ON(rt_mutex_is_locked(lock));
990 : : #ifdef CONFIG_DEBUG_RT_MUTEXES
991 : : lock->magic = NULL;
992 : : #endif
993 : 0 : }
994 : :
995 : : EXPORT_SYMBOL_GPL(rt_mutex_destroy);
996 : :
997 : : /**
998 : : * __rt_mutex_init - initialize the rt lock
999 : : *
1000 : : * @lock: the rt lock to be initialized
1001 : : *
1002 : : * Initialize the rt lock to unlocked state.
1003 : : *
1004 : : * Initializing of a locked rt lock is not allowed
1005 : : */
1006 : 0 : void __rt_mutex_init(struct rt_mutex *lock, const char *name)
1007 : : {
1008 : 0 : lock->owner = NULL;
1009 : 0 : raw_spin_lock_init(&lock->wait_lock);
1010 : 0 : lock->waiters = RB_ROOT;
1011 : 0 : lock->waiters_leftmost = NULL;
1012 : :
1013 : : debug_rt_mutex_init(lock, name);
1014 : 0 : }
1015 : : EXPORT_SYMBOL_GPL(__rt_mutex_init);
1016 : :
1017 : : /**
1018 : : * rt_mutex_init_proxy_locked - initialize and lock a rt_mutex on behalf of a
1019 : : * proxy owner
1020 : : *
1021 : : * @lock: the rt_mutex to be locked
1022 : : * @proxy_owner:the task to set as owner
1023 : : *
1024 : : * No locking. Caller has to do serializing itself
1025 : : * Special API call for PI-futex support
1026 : : */
1027 : 0 : void rt_mutex_init_proxy_locked(struct rt_mutex *lock,
1028 : : struct task_struct *proxy_owner)
1029 : : {
1030 : : __rt_mutex_init(lock, NULL);
1031 : : debug_rt_mutex_proxy_lock(lock, proxy_owner);
1032 : : rt_mutex_set_owner(lock, proxy_owner);
1033 : : rt_mutex_deadlock_account_lock(lock, proxy_owner);
1034 : 0 : }
1035 : :
1036 : : /**
1037 : : * rt_mutex_proxy_unlock - release a lock on behalf of owner
1038 : : *
1039 : : * @lock: the rt_mutex to be locked
1040 : : *
1041 : : * No locking. Caller has to do serializing itself
1042 : : * Special API call for PI-futex support
1043 : : */
1044 : 0 : void rt_mutex_proxy_unlock(struct rt_mutex *lock,
1045 : : struct task_struct *proxy_owner)
1046 : : {
1047 : : debug_rt_mutex_proxy_unlock(lock);
1048 : : rt_mutex_set_owner(lock, NULL);
1049 : : rt_mutex_deadlock_account_unlock(proxy_owner);
1050 : 0 : }
1051 : :
1052 : : /**
1053 : : * rt_mutex_start_proxy_lock() - Start lock acquisition for another task
1054 : : * @lock: the rt_mutex to take
1055 : : * @waiter: the pre-initialized rt_mutex_waiter
1056 : : * @task: the task to prepare
1057 : : * @detect_deadlock: perform deadlock detection (1) or not (0)
1058 : : *
1059 : : * Returns:
1060 : : * 0 - task blocked on lock
1061 : : * 1 - acquired the lock for task, caller should wake it up
1062 : : * <0 - error
1063 : : *
1064 : : * Special API call for FUTEX_REQUEUE_PI support.
1065 : : */
1066 : 0 : int rt_mutex_start_proxy_lock(struct rt_mutex *lock,
1067 : : struct rt_mutex_waiter *waiter,
1068 : : struct task_struct *task, int detect_deadlock)
1069 : : {
1070 : : int ret;
1071 : :
1072 : 0 : raw_spin_lock(&lock->wait_lock);
1073 : :
1074 [ # # ]: 0 : if (try_to_take_rt_mutex(lock, task, NULL)) {
1075 : : raw_spin_unlock(&lock->wait_lock);
1076 : 0 : return 1;
1077 : : }
1078 : :
1079 : 0 : ret = task_blocks_on_rt_mutex(lock, waiter, task, detect_deadlock);
1080 : :
1081 [ # # ][ # # ]: 0 : if (ret && !rt_mutex_owner(lock)) {
1082 : : /*
1083 : : * Reset the return value. We might have
1084 : : * returned with -EDEADLK and the owner
1085 : : * released the lock while we were walking the
1086 : : * pi chain. Let the waiter sort it out.
1087 : : */
1088 : : ret = 0;
1089 : : }
1090 : :
1091 [ # # ]: 0 : if (unlikely(ret))
1092 : 0 : remove_waiter(lock, waiter);
1093 : :
1094 : : raw_spin_unlock(&lock->wait_lock);
1095 : :
1096 : : debug_rt_mutex_print_deadlock(waiter);
1097 : :
1098 : 0 : return ret;
1099 : : }
1100 : :
1101 : : /**
1102 : : * rt_mutex_next_owner - return the next owner of the lock
1103 : : *
1104 : : * @lock: the rt lock query
1105 : : *
1106 : : * Returns the next owner of the lock or NULL
1107 : : *
1108 : : * Caller has to serialize against other accessors to the lock
1109 : : * itself.
1110 : : *
1111 : : * Special API call for PI-futex support
1112 : : */
1113 : 0 : struct task_struct *rt_mutex_next_owner(struct rt_mutex *lock)
1114 : : {
1115 [ # # ]: 0 : if (!rt_mutex_has_waiters(lock))
1116 : : return NULL;
1117 : :
1118 : 0 : return rt_mutex_top_waiter(lock)->task;
1119 : : }
1120 : :
1121 : : /**
1122 : : * rt_mutex_finish_proxy_lock() - Complete lock acquisition
1123 : : * @lock: the rt_mutex we were woken on
1124 : : * @to: the timeout, null if none. hrtimer should already have
1125 : : * been started.
1126 : : * @waiter: the pre-initialized rt_mutex_waiter
1127 : : * @detect_deadlock: perform deadlock detection (1) or not (0)
1128 : : *
1129 : : * Complete the lock acquisition started our behalf by another thread.
1130 : : *
1131 : : * Returns:
1132 : : * 0 - success
1133 : : * <0 - error, one of -EINTR, -ETIMEDOUT, or -EDEADLK
1134 : : *
1135 : : * Special API call for PI-futex requeue support
1136 : : */
1137 : 0 : int rt_mutex_finish_proxy_lock(struct rt_mutex *lock,
1138 : : struct hrtimer_sleeper *to,
1139 : : struct rt_mutex_waiter *waiter,
1140 : : int detect_deadlock)
1141 : : {
1142 : : int ret;
1143 : :
1144 : 0 : raw_spin_lock(&lock->wait_lock);
1145 : :
1146 : 0 : set_current_state(TASK_INTERRUPTIBLE);
1147 : :
1148 : 0 : ret = __rt_mutex_slowlock(lock, TASK_INTERRUPTIBLE, to, waiter);
1149 : :
1150 : 0 : set_current_state(TASK_RUNNING);
1151 : :
1152 [ # # ]: 0 : if (unlikely(ret))
1153 : 0 : remove_waiter(lock, waiter);
1154 : :
1155 : : /*
1156 : : * try_to_take_rt_mutex() sets the waiter bit unconditionally. We might
1157 : : * have to fix that up.
1158 : : */
1159 : : fixup_rt_mutex_waiters(lock);
1160 : :
1161 : : raw_spin_unlock(&lock->wait_lock);
1162 : :
1163 : 0 : return ret;
1164 : : }
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