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1 | /* | |
2 | * kernel/mutex.c | |
3 | * | |
4 | * Mutexes: blocking mutual exclusion locks | |
5 | * | |
6 | * Started by Ingo Molnar: | |
7 | * | |
8 | * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> | |
9 | * | |
10 | * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and | |
11 | * David Howells for suggestions and improvements. | |
12 | * | |
13 | * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline | |
14 | * from the -rt tree, where it was originally implemented for rtmutexes | |
15 | * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale | |
16 | * and Sven Dietrich. | |
17 | * | |
18 | * Also see Documentation/mutex-design.txt. | |
19 | */ | |
20 | #include <linux/mutex.h> | |
21 | #include <linux/sched.h> | |
22 | #include <linux/module.h> | |
23 | #include <linux/spinlock.h> | |
24 | #include <linux/interrupt.h> | |
25 | #include <linux/debug_locks.h> | |
26 | ||
27 | /* | |
28 | * In the DEBUG case we are using the "NULL fastpath" for mutexes, | |
29 | * which forces all calls into the slowpath: | |
30 | */ | |
31 | #ifdef CONFIG_DEBUG_MUTEXES | |
32 | # include "mutex-debug.h" | |
33 | # include <asm-generic/mutex-null.h> | |
34 | #else | |
35 | # include "mutex.h" | |
36 | # include <asm/mutex.h> | |
37 | #endif | |
38 | ||
39 | void | |
40 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) | |
41 | { | |
42 | atomic_set(&lock->count, 1); | |
43 | spin_lock_init(&lock->wait_lock); | |
44 | INIT_LIST_HEAD(&lock->wait_list); | |
45 | mutex_clear_owner(lock); | |
46 | ||
47 | debug_mutex_init(lock, name, key); | |
48 | } | |
49 | ||
50 | EXPORT_SYMBOL(__mutex_init); | |
51 | ||
52 | #ifndef CONFIG_DEBUG_LOCK_ALLOC | |
53 | /* | |
54 | * We split the mutex lock/unlock logic into separate fastpath and | |
55 | * slowpath functions, to reduce the register pressure on the fastpath. | |
56 | * We also put the fastpath first in the kernel image, to make sure the | |
57 | * branch is predicted by the CPU as default-untaken. | |
58 | */ | |
59 | static __used noinline void __sched | |
60 | __mutex_lock_slowpath(atomic_t *lock_count); | |
61 | ||
62 | /** | |
63 | * mutex_lock - acquire the mutex | |
64 | * @lock: the mutex to be acquired | |
65 | * | |
66 | * Lock the mutex exclusively for this task. If the mutex is not | |
67 | * available right now, it will sleep until it can get it. | |
68 | * | |
69 | * The mutex must later on be released by the same task that | |
70 | * acquired it. Recursive locking is not allowed. The task | |
71 | * may not exit without first unlocking the mutex. Also, kernel | |
72 | * memory where the mutex resides mutex must not be freed with | |
73 | * the mutex still locked. The mutex must first be initialized | |
74 | * (or statically defined) before it can be locked. memset()-ing | |
75 | * the mutex to 0 is not allowed. | |
76 | * | |
77 | * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging | |
78 | * checks that will enforce the restrictions and will also do | |
79 | * deadlock debugging. ) | |
80 | * | |
81 | * This function is similar to (but not equivalent to) down(). | |
82 | */ | |
83 | void __sched mutex_lock(struct mutex *lock) | |
84 | { | |
85 | might_sleep(); | |
86 | /* | |
87 | * The locking fastpath is the 1->0 transition from | |
88 | * 'unlocked' into 'locked' state. | |
89 | */ | |
90 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); | |
91 | mutex_set_owner(lock); | |
92 | } | |
93 | ||
94 | EXPORT_SYMBOL(mutex_lock); | |
95 | #endif | |
96 | ||
97 | static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); | |
98 | ||
99 | /** | |
100 | * mutex_unlock - release the mutex | |
101 | * @lock: the mutex to be released | |
102 | * | |
103 | * Unlock a mutex that has been locked by this task previously. | |
104 | * | |
105 | * This function must not be used in interrupt context. Unlocking | |
106 | * of a not locked mutex is not allowed. | |
107 | * | |
108 | * This function is similar to (but not equivalent to) up(). | |
109 | */ | |
110 | void __sched mutex_unlock(struct mutex *lock) | |
111 | { | |
112 | /* | |
113 | * The unlocking fastpath is the 0->1 transition from 'locked' | |
114 | * into 'unlocked' state: | |
115 | */ | |
116 | #ifndef CONFIG_DEBUG_MUTEXES | |
117 | /* | |
118 | * When debugging is enabled we must not clear the owner before time, | |
119 | * the slow path will always be taken, and that clears the owner field | |
120 | * after verifying that it was indeed current. | |
121 | */ | |
122 | mutex_clear_owner(lock); | |
123 | #endif | |
124 | __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath); | |
125 | } | |
126 | ||
127 | EXPORT_SYMBOL(mutex_unlock); | |
128 | ||
129 | /* | |
130 | * Lock a mutex (possibly interruptible), slowpath: | |
131 | */ | |
132 | static inline int __sched | |
133 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, | |
134 | unsigned long ip) | |
135 | { | |
136 | struct task_struct *task = current; | |
137 | struct mutex_waiter waiter; | |
138 | unsigned long flags; | |
139 | ||
140 | preempt_disable(); | |
141 | mutex_acquire(&lock->dep_map, subclass, 0, ip); | |
142 | ||
143 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER | |
144 | /* | |
145 | * Optimistic spinning. | |
146 | * | |
147 | * We try to spin for acquisition when we find that there are no | |
148 | * pending waiters and the lock owner is currently running on a | |
149 | * (different) CPU. | |
150 | * | |
151 | * The rationale is that if the lock owner is running, it is likely to | |
152 | * release the lock soon. | |
153 | * | |
154 | * Since this needs the lock owner, and this mutex implementation | |
155 | * doesn't track the owner atomically in the lock field, we need to | |
156 | * track it non-atomically. | |
157 | * | |
158 | * We can't do this for DEBUG_MUTEXES because that relies on wait_lock | |
159 | * to serialize everything. | |
160 | */ | |
161 | ||
162 | for (;;) { | |
163 | struct thread_info *owner; | |
164 | ||
165 | /* | |
166 | * If we own the BKL, then don't spin. The owner of | |
167 | * the mutex might be waiting on us to release the BKL. | |
168 | */ | |
169 | if (unlikely(current->lock_depth >= 0)) | |
170 | break; | |
171 | ||
172 | /* | |
173 | * If there's an owner, wait for it to either | |
174 | * release the lock or go to sleep. | |
175 | */ | |
176 | owner = ACCESS_ONCE(lock->owner); | |
177 | if (owner && !mutex_spin_on_owner(lock, owner)) | |
178 | break; | |
179 | ||
180 | if (atomic_cmpxchg(&lock->count, 1, 0) == 1) { | |
181 | lock_acquired(&lock->dep_map, ip); | |
182 | mutex_set_owner(lock); | |
183 | preempt_enable(); | |
184 | return 0; | |
185 | } | |
186 | ||
187 | /* | |
188 | * When there's no owner, we might have preempted between the | |
189 | * owner acquiring the lock and setting the owner field. If | |
190 | * we're an RT task that will live-lock because we won't let | |
191 | * the owner complete. | |
192 | */ | |
193 | if (!owner && (need_resched() || rt_task(task))) | |
194 | break; | |
195 | ||
196 | /* | |
197 | * The cpu_relax() call is a compiler barrier which forces | |
198 | * everything in this loop to be re-loaded. We don't need | |
199 | * memory barriers as we'll eventually observe the right | |
200 | * values at the cost of a few extra spins. | |
201 | */ | |
202 | cpu_relax(); | |
203 | } | |
204 | #endif | |
205 | spin_lock_mutex(&lock->wait_lock, flags); | |
206 | ||
207 | debug_mutex_lock_common(lock, &waiter); | |
208 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); | |
209 | ||
210 | /* add waiting tasks to the end of the waitqueue (FIFO): */ | |
211 | list_add_tail(&waiter.list, &lock->wait_list); | |
212 | waiter.task = task; | |
213 | ||
214 | if (atomic_xchg(&lock->count, -1) == 1) | |
215 | goto done; | |
216 | ||
217 | lock_contended(&lock->dep_map, ip); | |
218 | ||
219 | for (;;) { | |
220 | /* | |
221 | * Lets try to take the lock again - this is needed even if | |
222 | * we get here for the first time (shortly after failing to | |
223 | * acquire the lock), to make sure that we get a wakeup once | |
224 | * it's unlocked. Later on, if we sleep, this is the | |
225 | * operation that gives us the lock. We xchg it to -1, so | |
226 | * that when we release the lock, we properly wake up the | |
227 | * other waiters: | |
228 | */ | |
229 | if (atomic_xchg(&lock->count, -1) == 1) | |
230 | break; | |
231 | ||
232 | /* | |
233 | * got a signal? (This code gets eliminated in the | |
234 | * TASK_UNINTERRUPTIBLE case.) | |
235 | */ | |
236 | if (unlikely(signal_pending_state(state, task))) { | |
237 | mutex_remove_waiter(lock, &waiter, | |
238 | task_thread_info(task)); | |
239 | mutex_release(&lock->dep_map, 1, ip); | |
240 | spin_unlock_mutex(&lock->wait_lock, flags); | |
241 | ||
242 | debug_mutex_free_waiter(&waiter); | |
243 | preempt_enable(); | |
244 | return -EINTR; | |
245 | } | |
246 | __set_task_state(task, state); | |
247 | ||
248 | /* didnt get the lock, go to sleep: */ | |
249 | spin_unlock_mutex(&lock->wait_lock, flags); | |
250 | preempt_enable_no_resched(); | |
251 | schedule(); | |
252 | preempt_disable(); | |
253 | spin_lock_mutex(&lock->wait_lock, flags); | |
254 | } | |
255 | ||
256 | done: | |
257 | lock_acquired(&lock->dep_map, ip); | |
258 | /* got the lock - rejoice! */ | |
259 | mutex_remove_waiter(lock, &waiter, current_thread_info()); | |
260 | mutex_set_owner(lock); | |
261 | ||
262 | /* set it to 0 if there are no waiters left: */ | |
263 | if (likely(list_empty(&lock->wait_list))) | |
264 | atomic_set(&lock->count, 0); | |
265 | ||
266 | spin_unlock_mutex(&lock->wait_lock, flags); | |
267 | ||
268 | debug_mutex_free_waiter(&waiter); | |
269 | preempt_enable(); | |
270 | ||
271 | return 0; | |
272 | } | |
273 | ||
274 | #ifdef CONFIG_DEBUG_LOCK_ALLOC | |
275 | void __sched | |
276 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) | |
277 | { | |
278 | might_sleep(); | |
279 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_); | |
280 | } | |
281 | ||
282 | EXPORT_SYMBOL_GPL(mutex_lock_nested); | |
283 | ||
284 | int __sched | |
285 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) | |
286 | { | |
287 | might_sleep(); | |
288 | return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_); | |
289 | } | |
290 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); | |
291 | ||
292 | int __sched | |
293 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) | |
294 | { | |
295 | might_sleep(); | |
296 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, | |
297 | subclass, _RET_IP_); | |
298 | } | |
299 | ||
300 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); | |
301 | #endif | |
302 | ||
303 | /* | |
304 | * Release the lock, slowpath: | |
305 | */ | |
306 | static inline void | |
307 | __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) | |
308 | { | |
309 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
310 | unsigned long flags; | |
311 | ||
312 | spin_lock_mutex(&lock->wait_lock, flags); | |
313 | mutex_release(&lock->dep_map, nested, _RET_IP_); | |
314 | debug_mutex_unlock(lock); | |
315 | ||
316 | /* | |
317 | * some architectures leave the lock unlocked in the fastpath failure | |
318 | * case, others need to leave it locked. In the later case we have to | |
319 | * unlock it here | |
320 | */ | |
321 | if (__mutex_slowpath_needs_to_unlock()) | |
322 | atomic_set(&lock->count, 1); | |
323 | ||
324 | if (!list_empty(&lock->wait_list)) { | |
325 | /* get the first entry from the wait-list: */ | |
326 | struct mutex_waiter *waiter = | |
327 | list_entry(lock->wait_list.next, | |
328 | struct mutex_waiter, list); | |
329 | ||
330 | debug_mutex_wake_waiter(lock, waiter); | |
331 | ||
332 | wake_up_process(waiter->task); | |
333 | } | |
334 | ||
335 | spin_unlock_mutex(&lock->wait_lock, flags); | |
336 | } | |
337 | ||
338 | /* | |
339 | * Release the lock, slowpath: | |
340 | */ | |
341 | static __used noinline void | |
342 | __mutex_unlock_slowpath(atomic_t *lock_count) | |
343 | { | |
344 | __mutex_unlock_common_slowpath(lock_count, 1); | |
345 | } | |
346 | ||
347 | #ifndef CONFIG_DEBUG_LOCK_ALLOC | |
348 | /* | |
349 | * Here come the less common (and hence less performance-critical) APIs: | |
350 | * mutex_lock_interruptible() and mutex_trylock(). | |
351 | */ | |
352 | static noinline int __sched | |
353 | __mutex_lock_killable_slowpath(atomic_t *lock_count); | |
354 | ||
355 | static noinline int __sched | |
356 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); | |
357 | ||
358 | /** | |
359 | * mutex_lock_interruptible - acquire the mutex, interruptible | |
360 | * @lock: the mutex to be acquired | |
361 | * | |
362 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has | |
363 | * been acquired or sleep until the mutex becomes available. If a | |
364 | * signal arrives while waiting for the lock then this function | |
365 | * returns -EINTR. | |
366 | * | |
367 | * This function is similar to (but not equivalent to) down_interruptible(). | |
368 | */ | |
369 | int __sched mutex_lock_interruptible(struct mutex *lock) | |
370 | { | |
371 | int ret; | |
372 | ||
373 | might_sleep(); | |
374 | ret = __mutex_fastpath_lock_retval | |
375 | (&lock->count, __mutex_lock_interruptible_slowpath); | |
376 | if (!ret) | |
377 | mutex_set_owner(lock); | |
378 | ||
379 | return ret; | |
380 | } | |
381 | ||
382 | EXPORT_SYMBOL(mutex_lock_interruptible); | |
383 | ||
384 | int __sched mutex_lock_killable(struct mutex *lock) | |
385 | { | |
386 | int ret; | |
387 | ||
388 | might_sleep(); | |
389 | ret = __mutex_fastpath_lock_retval | |
390 | (&lock->count, __mutex_lock_killable_slowpath); | |
391 | if (!ret) | |
392 | mutex_set_owner(lock); | |
393 | ||
394 | return ret; | |
395 | } | |
396 | EXPORT_SYMBOL(mutex_lock_killable); | |
397 | ||
398 | static __used noinline void __sched | |
399 | __mutex_lock_slowpath(atomic_t *lock_count) | |
400 | { | |
401 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
402 | ||
403 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_); | |
404 | } | |
405 | ||
406 | static noinline int __sched | |
407 | __mutex_lock_killable_slowpath(atomic_t *lock_count) | |
408 | { | |
409 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
410 | ||
411 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_); | |
412 | } | |
413 | ||
414 | static noinline int __sched | |
415 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) | |
416 | { | |
417 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
418 | ||
419 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_); | |
420 | } | |
421 | #endif | |
422 | ||
423 | /* | |
424 | * Spinlock based trylock, we take the spinlock and check whether we | |
425 | * can get the lock: | |
426 | */ | |
427 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) | |
428 | { | |
429 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
430 | unsigned long flags; | |
431 | int prev; | |
432 | ||
433 | spin_lock_mutex(&lock->wait_lock, flags); | |
434 | ||
435 | prev = atomic_xchg(&lock->count, -1); | |
436 | if (likely(prev == 1)) { | |
437 | mutex_set_owner(lock); | |
438 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); | |
439 | } | |
440 | ||
441 | /* Set it back to 0 if there are no waiters: */ | |
442 | if (likely(list_empty(&lock->wait_list))) | |
443 | atomic_set(&lock->count, 0); | |
444 | ||
445 | spin_unlock_mutex(&lock->wait_lock, flags); | |
446 | ||
447 | return prev == 1; | |
448 | } | |
449 | ||
450 | /** | |
451 | * mutex_trylock - try to acquire the mutex, without waiting | |
452 | * @lock: the mutex to be acquired | |
453 | * | |
454 | * Try to acquire the mutex atomically. Returns 1 if the mutex | |
455 | * has been acquired successfully, and 0 on contention. | |
456 | * | |
457 | * NOTE: this function follows the spin_trylock() convention, so | |
458 | * it is negated from the down_trylock() return values! Be careful | |
459 | * about this when converting semaphore users to mutexes. | |
460 | * | |
461 | * This function must not be used in interrupt context. The | |
462 | * mutex must be released by the same task that acquired it. | |
463 | */ | |
464 | int __sched mutex_trylock(struct mutex *lock) | |
465 | { | |
466 | int ret; | |
467 | ||
468 | ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath); | |
469 | if (ret) | |
470 | mutex_set_owner(lock); | |
471 | ||
472 | return ret; | |
473 | } | |
474 | EXPORT_SYMBOL(mutex_trylock); | |
475 | ||
476 | /** | |
477 | * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 | |
478 | * @cnt: the atomic which we are to dec | |
479 | * @lock: the mutex to return holding if we dec to 0 | |
480 | * | |
481 | * return true and hold lock if we dec to 0, return false otherwise | |
482 | */ | |
483 | int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) | |
484 | { | |
485 | /* dec if we can't possibly hit 0 */ | |
486 | if (atomic_add_unless(cnt, -1, 1)) | |
487 | return 0; | |
488 | /* we might hit 0, so take the lock */ | |
489 | mutex_lock(lock); | |
490 | if (!atomic_dec_and_test(cnt)) { | |
491 | /* when we actually did the dec, we didn't hit 0 */ | |
492 | mutex_unlock(lock); | |
493 | return 0; | |
494 | } | |
495 | /* we hit 0, and we hold the lock */ | |
496 | return 1; | |
497 | } | |
498 | EXPORT_SYMBOL(atomic_dec_and_mutex_lock); |