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6053ee3b IM |
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 | * | |
0d66bf6d PZ |
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 | * | |
6053ee3b IM |
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> | |
9a11b49a | 25 | #include <linux/debug_locks.h> |
6053ee3b IM |
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 | ||
ef5d4707 IM |
39 | void |
40 | __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key) | |
6053ee3b IM |
41 | { |
42 | atomic_set(&lock->count, 1); | |
43 | spin_lock_init(&lock->wait_lock); | |
44 | INIT_LIST_HEAD(&lock->wait_list); | |
0d66bf6d | 45 | mutex_clear_owner(lock); |
6053ee3b | 46 | |
ef5d4707 | 47 | debug_mutex_init(lock, name, key); |
6053ee3b IM |
48 | } |
49 | ||
50 | EXPORT_SYMBOL(__mutex_init); | |
51 | ||
e4564f79 | 52 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
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 | */ | |
7918baa5 | 59 | static __used noinline void __sched |
9a11b49a | 60 | __mutex_lock_slowpath(atomic_t *lock_count); |
6053ee3b | 61 | |
ef5dc121 | 62 | /** |
6053ee3b IM |
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 | */ | |
b09d2501 | 83 | void __sched mutex_lock(struct mutex *lock) |
6053ee3b | 84 | { |
c544bdb1 | 85 | might_sleep(); |
6053ee3b IM |
86 | /* |
87 | * The locking fastpath is the 1->0 transition from | |
88 | * 'unlocked' into 'locked' state. | |
6053ee3b IM |
89 | */ |
90 | __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath); | |
0d66bf6d | 91 | mutex_set_owner(lock); |
6053ee3b IM |
92 | } |
93 | ||
94 | EXPORT_SYMBOL(mutex_lock); | |
e4564f79 | 95 | #endif |
6053ee3b | 96 | |
7918baa5 | 97 | static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); |
6053ee3b | 98 | |
ef5dc121 | 99 | /** |
6053ee3b IM |
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 | */ | |
7ad5b3a5 | 110 | void __sched mutex_unlock(struct mutex *lock) |
6053ee3b IM |
111 | { |
112 | /* | |
113 | * The unlocking fastpath is the 0->1 transition from 'locked' | |
114 | * into 'unlocked' state: | |
6053ee3b | 115 | */ |
0d66bf6d PZ |
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 | |
6053ee3b IM |
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 | |
e4564f79 PZ |
133 | __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, |
134 | unsigned long ip) | |
6053ee3b IM |
135 | { |
136 | struct task_struct *task = current; | |
137 | struct mutex_waiter waiter; | |
1fb00c6c | 138 | unsigned long flags; |
6053ee3b | 139 | |
41719b03 | 140 | preempt_disable(); |
0d66bf6d | 141 | mutex_acquire(&lock->dep_map, subclass, 0, ip); |
c0226027 FW |
142 | |
143 | #ifdef CONFIG_MUTEX_SPIN_ON_OWNER | |
0d66bf6d PZ |
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 (;;) { | |
c6eb3dda | 163 | struct task_struct *owner; |
0d66bf6d | 164 | |
0d66bf6d PZ |
165 | /* |
166 | * If there's an owner, wait for it to either | |
167 | * release the lock or go to sleep. | |
168 | */ | |
169 | owner = ACCESS_ONCE(lock->owner); | |
170 | if (owner && !mutex_spin_on_owner(lock, owner)) | |
171 | break; | |
172 | ||
ac6e60ee CM |
173 | if (atomic_cmpxchg(&lock->count, 1, 0) == 1) { |
174 | lock_acquired(&lock->dep_map, ip); | |
175 | mutex_set_owner(lock); | |
176 | preempt_enable(); | |
177 | return 0; | |
178 | } | |
179 | ||
0d66bf6d PZ |
180 | /* |
181 | * When there's no owner, we might have preempted between the | |
182 | * owner acquiring the lock and setting the owner field. If | |
183 | * we're an RT task that will live-lock because we won't let | |
184 | * the owner complete. | |
185 | */ | |
186 | if (!owner && (need_resched() || rt_task(task))) | |
187 | break; | |
188 | ||
0d66bf6d PZ |
189 | /* |
190 | * The cpu_relax() call is a compiler barrier which forces | |
191 | * everything in this loop to be re-loaded. We don't need | |
192 | * memory barriers as we'll eventually observe the right | |
193 | * values at the cost of a few extra spins. | |
194 | */ | |
335d7afb | 195 | arch_mutex_cpu_relax(); |
0d66bf6d PZ |
196 | } |
197 | #endif | |
1fb00c6c | 198 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b | 199 | |
9a11b49a | 200 | debug_mutex_lock_common(lock, &waiter); |
c9f4f06d | 201 | debug_mutex_add_waiter(lock, &waiter, task_thread_info(task)); |
6053ee3b IM |
202 | |
203 | /* add waiting tasks to the end of the waitqueue (FIFO): */ | |
204 | list_add_tail(&waiter.list, &lock->wait_list); | |
205 | waiter.task = task; | |
206 | ||
93d81d1a | 207 | if (atomic_xchg(&lock->count, -1) == 1) |
4fe87745 PZ |
208 | goto done; |
209 | ||
e4564f79 | 210 | lock_contended(&lock->dep_map, ip); |
4fe87745 | 211 | |
6053ee3b IM |
212 | for (;;) { |
213 | /* | |
214 | * Lets try to take the lock again - this is needed even if | |
215 | * we get here for the first time (shortly after failing to | |
216 | * acquire the lock), to make sure that we get a wakeup once | |
217 | * it's unlocked. Later on, if we sleep, this is the | |
218 | * operation that gives us the lock. We xchg it to -1, so | |
219 | * that when we release the lock, we properly wake up the | |
220 | * other waiters: | |
221 | */ | |
93d81d1a | 222 | if (atomic_xchg(&lock->count, -1) == 1) |
6053ee3b IM |
223 | break; |
224 | ||
225 | /* | |
226 | * got a signal? (This code gets eliminated in the | |
227 | * TASK_UNINTERRUPTIBLE case.) | |
228 | */ | |
6ad36762 | 229 | if (unlikely(signal_pending_state(state, task))) { |
ad776537 LH |
230 | mutex_remove_waiter(lock, &waiter, |
231 | task_thread_info(task)); | |
e4564f79 | 232 | mutex_release(&lock->dep_map, 1, ip); |
1fb00c6c | 233 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
234 | |
235 | debug_mutex_free_waiter(&waiter); | |
41719b03 | 236 | preempt_enable(); |
6053ee3b IM |
237 | return -EINTR; |
238 | } | |
239 | __set_task_state(task, state); | |
240 | ||
25985edc | 241 | /* didn't get the lock, go to sleep: */ |
1fb00c6c | 242 | spin_unlock_mutex(&lock->wait_lock, flags); |
ff743345 PZ |
243 | preempt_enable_no_resched(); |
244 | schedule(); | |
245 | preempt_disable(); | |
1fb00c6c | 246 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
247 | } |
248 | ||
4fe87745 | 249 | done: |
c7e78cff | 250 | lock_acquired(&lock->dep_map, ip); |
6053ee3b | 251 | /* got the lock - rejoice! */ |
0d66bf6d PZ |
252 | mutex_remove_waiter(lock, &waiter, current_thread_info()); |
253 | mutex_set_owner(lock); | |
6053ee3b IM |
254 | |
255 | /* set it to 0 if there are no waiters left: */ | |
256 | if (likely(list_empty(&lock->wait_list))) | |
257 | atomic_set(&lock->count, 0); | |
258 | ||
1fb00c6c | 259 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
260 | |
261 | debug_mutex_free_waiter(&waiter); | |
41719b03 | 262 | preempt_enable(); |
6053ee3b | 263 | |
6053ee3b IM |
264 | return 0; |
265 | } | |
266 | ||
ef5d4707 IM |
267 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
268 | void __sched | |
269 | mutex_lock_nested(struct mutex *lock, unsigned int subclass) | |
270 | { | |
271 | might_sleep(); | |
e4564f79 | 272 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_); |
ef5d4707 IM |
273 | } |
274 | ||
275 | EXPORT_SYMBOL_GPL(mutex_lock_nested); | |
d63a5a74 | 276 | |
ad776537 LH |
277 | int __sched |
278 | mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) | |
279 | { | |
280 | might_sleep(); | |
281 | return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_); | |
282 | } | |
283 | EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); | |
284 | ||
d63a5a74 N |
285 | int __sched |
286 | mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) | |
287 | { | |
288 | might_sleep(); | |
0d66bf6d PZ |
289 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, |
290 | subclass, _RET_IP_); | |
d63a5a74 N |
291 | } |
292 | ||
293 | EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested); | |
ef5d4707 IM |
294 | #endif |
295 | ||
6053ee3b IM |
296 | /* |
297 | * Release the lock, slowpath: | |
298 | */ | |
7ad5b3a5 | 299 | static inline void |
ef5d4707 | 300 | __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested) |
6053ee3b | 301 | { |
02706647 | 302 | struct mutex *lock = container_of(lock_count, struct mutex, count); |
1fb00c6c | 303 | unsigned long flags; |
6053ee3b | 304 | |
1fb00c6c | 305 | spin_lock_mutex(&lock->wait_lock, flags); |
ef5d4707 | 306 | mutex_release(&lock->dep_map, nested, _RET_IP_); |
9a11b49a | 307 | debug_mutex_unlock(lock); |
6053ee3b IM |
308 | |
309 | /* | |
310 | * some architectures leave the lock unlocked in the fastpath failure | |
311 | * case, others need to leave it locked. In the later case we have to | |
312 | * unlock it here | |
313 | */ | |
314 | if (__mutex_slowpath_needs_to_unlock()) | |
315 | atomic_set(&lock->count, 1); | |
316 | ||
6053ee3b IM |
317 | if (!list_empty(&lock->wait_list)) { |
318 | /* get the first entry from the wait-list: */ | |
319 | struct mutex_waiter *waiter = | |
320 | list_entry(lock->wait_list.next, | |
321 | struct mutex_waiter, list); | |
322 | ||
323 | debug_mutex_wake_waiter(lock, waiter); | |
324 | ||
325 | wake_up_process(waiter->task); | |
326 | } | |
327 | ||
1fb00c6c | 328 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
329 | } |
330 | ||
9a11b49a IM |
331 | /* |
332 | * Release the lock, slowpath: | |
333 | */ | |
7918baa5 | 334 | static __used noinline void |
9a11b49a IM |
335 | __mutex_unlock_slowpath(atomic_t *lock_count) |
336 | { | |
ef5d4707 | 337 | __mutex_unlock_common_slowpath(lock_count, 1); |
9a11b49a IM |
338 | } |
339 | ||
e4564f79 | 340 | #ifndef CONFIG_DEBUG_LOCK_ALLOC |
6053ee3b IM |
341 | /* |
342 | * Here come the less common (and hence less performance-critical) APIs: | |
343 | * mutex_lock_interruptible() and mutex_trylock(). | |
344 | */ | |
7ad5b3a5 | 345 | static noinline int __sched |
ad776537 LH |
346 | __mutex_lock_killable_slowpath(atomic_t *lock_count); |
347 | ||
7ad5b3a5 | 348 | static noinline int __sched |
9a11b49a | 349 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count); |
6053ee3b | 350 | |
ef5dc121 RD |
351 | /** |
352 | * mutex_lock_interruptible - acquire the mutex, interruptible | |
6053ee3b IM |
353 | * @lock: the mutex to be acquired |
354 | * | |
355 | * Lock the mutex like mutex_lock(), and return 0 if the mutex has | |
356 | * been acquired or sleep until the mutex becomes available. If a | |
357 | * signal arrives while waiting for the lock then this function | |
358 | * returns -EINTR. | |
359 | * | |
360 | * This function is similar to (but not equivalent to) down_interruptible(). | |
361 | */ | |
7ad5b3a5 | 362 | int __sched mutex_lock_interruptible(struct mutex *lock) |
6053ee3b | 363 | { |
0d66bf6d PZ |
364 | int ret; |
365 | ||
c544bdb1 | 366 | might_sleep(); |
0d66bf6d | 367 | ret = __mutex_fastpath_lock_retval |
6053ee3b | 368 | (&lock->count, __mutex_lock_interruptible_slowpath); |
0d66bf6d PZ |
369 | if (!ret) |
370 | mutex_set_owner(lock); | |
371 | ||
372 | return ret; | |
6053ee3b IM |
373 | } |
374 | ||
375 | EXPORT_SYMBOL(mutex_lock_interruptible); | |
376 | ||
7ad5b3a5 | 377 | int __sched mutex_lock_killable(struct mutex *lock) |
ad776537 | 378 | { |
0d66bf6d PZ |
379 | int ret; |
380 | ||
ad776537 | 381 | might_sleep(); |
0d66bf6d | 382 | ret = __mutex_fastpath_lock_retval |
ad776537 | 383 | (&lock->count, __mutex_lock_killable_slowpath); |
0d66bf6d PZ |
384 | if (!ret) |
385 | mutex_set_owner(lock); | |
386 | ||
387 | return ret; | |
ad776537 LH |
388 | } |
389 | EXPORT_SYMBOL(mutex_lock_killable); | |
390 | ||
7918baa5 | 391 | static __used noinline void __sched |
e4564f79 PZ |
392 | __mutex_lock_slowpath(atomic_t *lock_count) |
393 | { | |
394 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
395 | ||
396 | __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_); | |
397 | } | |
398 | ||
7ad5b3a5 | 399 | static noinline int __sched |
ad776537 LH |
400 | __mutex_lock_killable_slowpath(atomic_t *lock_count) |
401 | { | |
402 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
403 | ||
404 | return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_); | |
405 | } | |
406 | ||
7ad5b3a5 | 407 | static noinline int __sched |
9a11b49a | 408 | __mutex_lock_interruptible_slowpath(atomic_t *lock_count) |
6053ee3b IM |
409 | { |
410 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
411 | ||
e4564f79 | 412 | return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_); |
6053ee3b | 413 | } |
e4564f79 | 414 | #endif |
6053ee3b IM |
415 | |
416 | /* | |
417 | * Spinlock based trylock, we take the spinlock and check whether we | |
418 | * can get the lock: | |
419 | */ | |
420 | static inline int __mutex_trylock_slowpath(atomic_t *lock_count) | |
421 | { | |
422 | struct mutex *lock = container_of(lock_count, struct mutex, count); | |
1fb00c6c | 423 | unsigned long flags; |
6053ee3b IM |
424 | int prev; |
425 | ||
1fb00c6c | 426 | spin_lock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
427 | |
428 | prev = atomic_xchg(&lock->count, -1); | |
ef5d4707 | 429 | if (likely(prev == 1)) { |
0d66bf6d | 430 | mutex_set_owner(lock); |
ef5d4707 IM |
431 | mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_); |
432 | } | |
0d66bf6d | 433 | |
6053ee3b IM |
434 | /* Set it back to 0 if there are no waiters: */ |
435 | if (likely(list_empty(&lock->wait_list))) | |
436 | atomic_set(&lock->count, 0); | |
437 | ||
1fb00c6c | 438 | spin_unlock_mutex(&lock->wait_lock, flags); |
6053ee3b IM |
439 | |
440 | return prev == 1; | |
441 | } | |
442 | ||
ef5dc121 RD |
443 | /** |
444 | * mutex_trylock - try to acquire the mutex, without waiting | |
6053ee3b IM |
445 | * @lock: the mutex to be acquired |
446 | * | |
447 | * Try to acquire the mutex atomically. Returns 1 if the mutex | |
448 | * has been acquired successfully, and 0 on contention. | |
449 | * | |
450 | * NOTE: this function follows the spin_trylock() convention, so | |
ef5dc121 | 451 | * it is negated from the down_trylock() return values! Be careful |
6053ee3b IM |
452 | * about this when converting semaphore users to mutexes. |
453 | * | |
454 | * This function must not be used in interrupt context. The | |
455 | * mutex must be released by the same task that acquired it. | |
456 | */ | |
7ad5b3a5 | 457 | int __sched mutex_trylock(struct mutex *lock) |
6053ee3b | 458 | { |
0d66bf6d PZ |
459 | int ret; |
460 | ||
461 | ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath); | |
462 | if (ret) | |
463 | mutex_set_owner(lock); | |
464 | ||
465 | return ret; | |
6053ee3b | 466 | } |
6053ee3b | 467 | EXPORT_SYMBOL(mutex_trylock); |
a511e3f9 AM |
468 | |
469 | /** | |
470 | * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0 | |
471 | * @cnt: the atomic which we are to dec | |
472 | * @lock: the mutex to return holding if we dec to 0 | |
473 | * | |
474 | * return true and hold lock if we dec to 0, return false otherwise | |
475 | */ | |
476 | int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock) | |
477 | { | |
478 | /* dec if we can't possibly hit 0 */ | |
479 | if (atomic_add_unless(cnt, -1, 1)) | |
480 | return 0; | |
481 | /* we might hit 0, so take the lock */ | |
482 | mutex_lock(lock); | |
483 | if (!atomic_dec_and_test(cnt)) { | |
484 | /* when we actually did the dec, we didn't hit 0 */ | |
485 | mutex_unlock(lock); | |
486 | return 0; | |
487 | } | |
488 | /* we hit 0, and we hold the lock */ | |
489 | return 1; | |
490 | } | |
491 | EXPORT_SYMBOL(atomic_dec_and_mutex_lock); |