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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 /***
40 * mutex_init - initialize the mutex
41 * @lock: the mutex to be initialized
42 * @key: the lock_class_key for the class; used by mutex lock debugging
43 *
44 * Initialize the mutex to unlocked state.
45 *
46 * It is not allowed to initialize an already locked mutex.
47 */
48 void
49 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
50 {
51 atomic_set(&lock->count, 1);
52 spin_lock_init(&lock->wait_lock);
53 INIT_LIST_HEAD(&lock->wait_list);
54 mutex_clear_owner(lock);
55
56 debug_mutex_init(lock, name, key);
57 }
58
59 EXPORT_SYMBOL(__mutex_init);
60
61 #ifndef CONFIG_DEBUG_LOCK_ALLOC
62 /*
63 * We split the mutex lock/unlock logic into separate fastpath and
64 * slowpath functions, to reduce the register pressure on the fastpath.
65 * We also put the fastpath first in the kernel image, to make sure the
66 * branch is predicted by the CPU as default-untaken.
67 */
68 static __used noinline void __sched
69 __mutex_lock_slowpath(atomic_t *lock_count);
70
71 /***
72 * mutex_lock - acquire the mutex
73 * @lock: the mutex to be acquired
74 *
75 * Lock the mutex exclusively for this task. If the mutex is not
76 * available right now, it will sleep until it can get it.
77 *
78 * The mutex must later on be released by the same task that
79 * acquired it. Recursive locking is not allowed. The task
80 * may not exit without first unlocking the mutex. Also, kernel
81 * memory where the mutex resides mutex must not be freed with
82 * the mutex still locked. The mutex must first be initialized
83 * (or statically defined) before it can be locked. memset()-ing
84 * the mutex to 0 is not allowed.
85 *
86 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
87 * checks that will enforce the restrictions and will also do
88 * deadlock debugging. )
89 *
90 * This function is similar to (but not equivalent to) down().
91 */
92 void inline __sched mutex_lock(struct mutex *lock)
93 {
94 might_sleep();
95 /*
96 * The locking fastpath is the 1->0 transition from
97 * 'unlocked' into 'locked' state.
98 */
99 __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
100 mutex_set_owner(lock);
101 }
102
103 EXPORT_SYMBOL(mutex_lock);
104 #endif
105
106 static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
107
108 /***
109 * mutex_unlock - release the mutex
110 * @lock: the mutex to be released
111 *
112 * Unlock a mutex that has been locked by this task previously.
113 *
114 * This function must not be used in interrupt context. Unlocking
115 * of a not locked mutex is not allowed.
116 *
117 * This function is similar to (but not equivalent to) up().
118 */
119 void __sched mutex_unlock(struct mutex *lock)
120 {
121 /*
122 * The unlocking fastpath is the 0->1 transition from 'locked'
123 * into 'unlocked' state:
124 */
125 #ifndef CONFIG_DEBUG_MUTEXES
126 /*
127 * When debugging is enabled we must not clear the owner before time,
128 * the slow path will always be taken, and that clears the owner field
129 * after verifying that it was indeed current.
130 */
131 mutex_clear_owner(lock);
132 #endif
133 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
134 }
135
136 EXPORT_SYMBOL(mutex_unlock);
137
138 /*
139 * Lock a mutex (possibly interruptible), slowpath:
140 */
141 static inline int __sched
142 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
143 unsigned long ip)
144 {
145 struct task_struct *task = current;
146 struct mutex_waiter waiter;
147 unsigned long flags;
148
149 preempt_disable();
150 mutex_acquire(&lock->dep_map, subclass, 0, ip);
151 #if defined(CONFIG_SMP) && !defined(CONFIG_DEBUG_MUTEXES) && \
152 !defined(CONFIG_HAVE_DEFAULT_NO_SPIN_MUTEXES)
153 /*
154 * Optimistic spinning.
155 *
156 * We try to spin for acquisition when we find that there are no
157 * pending waiters and the lock owner is currently running on a
158 * (different) CPU.
159 *
160 * The rationale is that if the lock owner is running, it is likely to
161 * release the lock soon.
162 *
163 * Since this needs the lock owner, and this mutex implementation
164 * doesn't track the owner atomically in the lock field, we need to
165 * track it non-atomically.
166 *
167 * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
168 * to serialize everything.
169 */
170
171 for (;;) {
172 struct thread_info *owner;
173
174 /*
175 * If there's an owner, wait for it to either
176 * release the lock or go to sleep.
177 */
178 owner = ACCESS_ONCE(lock->owner);
179 if (owner && !mutex_spin_on_owner(lock, owner))
180 break;
181
182 if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {
183 lock_acquired(&lock->dep_map, ip);
184 mutex_set_owner(lock);
185 preempt_enable();
186 return 0;
187 }
188
189 /*
190 * When there's no owner, we might have preempted between the
191 * owner acquiring the lock and setting the owner field. If
192 * we're an RT task that will live-lock because we won't let
193 * the owner complete.
194 */
195 if (!owner && (need_resched() || rt_task(task)))
196 break;
197
198 /*
199 * The cpu_relax() call is a compiler barrier which forces
200 * everything in this loop to be re-loaded. We don't need
201 * memory barriers as we'll eventually observe the right
202 * values at the cost of a few extra spins.
203 */
204 cpu_relax();
205 }
206 #endif
207 spin_lock_mutex(&lock->wait_lock, flags);
208
209 debug_mutex_lock_common(lock, &waiter);
210 debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
211
212 /* add waiting tasks to the end of the waitqueue (FIFO): */
213 list_add_tail(&waiter.list, &lock->wait_list);
214 waiter.task = task;
215
216 if (atomic_xchg(&lock->count, -1) == 1)
217 goto done;
218
219 lock_contended(&lock->dep_map, ip);
220
221 for (;;) {
222 /*
223 * Lets try to take the lock again - this is needed even if
224 * we get here for the first time (shortly after failing to
225 * acquire the lock), to make sure that we get a wakeup once
226 * it's unlocked. Later on, if we sleep, this is the
227 * operation that gives us the lock. We xchg it to -1, so
228 * that when we release the lock, we properly wake up the
229 * other waiters:
230 */
231 if (atomic_xchg(&lock->count, -1) == 1)
232 break;
233
234 /*
235 * got a signal? (This code gets eliminated in the
236 * TASK_UNINTERRUPTIBLE case.)
237 */
238 if (unlikely(signal_pending_state(state, task))) {
239 mutex_remove_waiter(lock, &waiter,
240 task_thread_info(task));
241 mutex_release(&lock->dep_map, 1, ip);
242 spin_unlock_mutex(&lock->wait_lock, flags);
243
244 debug_mutex_free_waiter(&waiter);
245 preempt_enable();
246 return -EINTR;
247 }
248 __set_task_state(task, state);
249
250 /* didnt get the lock, go to sleep: */
251 spin_unlock_mutex(&lock->wait_lock, flags);
252 __schedule();
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, interruptable
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 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 to 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
475 EXPORT_SYMBOL(mutex_trylock);