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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 *
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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 *
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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>
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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
0e241ffd 42 * @key: the lock_class_key for the class; used by mutex lock debugging
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43 *
44 * Initialize the mutex to unlocked state.
45 *
46 * It is not allowed to initialize an already locked mutex.
47 */
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48void
49__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
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50{
51 atomic_set(&lock->count, 1);
52 spin_lock_init(&lock->wait_lock);
53 INIT_LIST_HEAD(&lock->wait_list);
0d66bf6d 54 mutex_clear_owner(lock);
6053ee3b 55
ef5d4707 56 debug_mutex_init(lock, name, key);
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57}
58
59EXPORT_SYMBOL(__mutex_init);
60
e4564f79 61#ifndef CONFIG_DEBUG_LOCK_ALLOC
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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 */
7918baa5 68static __used noinline void __sched
9a11b49a 69__mutex_lock_slowpath(atomic_t *lock_count);
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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 */
7ad5b3a5 92void inline __sched mutex_lock(struct mutex *lock)
6053ee3b 93{
c544bdb1 94 might_sleep();
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95 /*
96 * The locking fastpath is the 1->0 transition from
97 * 'unlocked' into 'locked' state.
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98 */
99 __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
0d66bf6d 100 mutex_set_owner(lock);
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101}
102
103EXPORT_SYMBOL(mutex_lock);
e4564f79 104#endif
6053ee3b 105
7918baa5 106static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
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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 */
7ad5b3a5 119void __sched mutex_unlock(struct mutex *lock)
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120{
121 /*
122 * The unlocking fastpath is the 0->1 transition from 'locked'
123 * into 'unlocked' state:
6053ee3b 124 */
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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
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133 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
134}
135
136EXPORT_SYMBOL(mutex_unlock);
137
138/*
139 * Lock a mutex (possibly interruptible), slowpath:
140 */
141static inline int __sched
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142__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
143 unsigned long ip)
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144{
145 struct task_struct *task = current;
146 struct mutex_waiter waiter;
1fb00c6c 147 unsigned long flags;
6053ee3b 148
41719b03 149 preempt_disable();
0d66bf6d 150 mutex_acquire(&lock->dep_map, subclass, 0, ip);
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151#if defined(CONFIG_SMP) && !defined(CONFIG_DEBUG_MUTEXES) && \
152 !defined(CONFIG_HAVE_DEFAULT_NO_SPIN_MUTEXES)
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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
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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
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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
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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
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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
1fb00c6c 207 spin_lock_mutex(&lock->wait_lock, flags);
6053ee3b 208
9a11b49a 209 debug_mutex_lock_common(lock, &waiter);
c9f4f06d 210 debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
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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
93d81d1a 216 if (atomic_xchg(&lock->count, -1) == 1)
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217 goto done;
218
e4564f79 219 lock_contended(&lock->dep_map, ip);
4fe87745 220
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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 */
93d81d1a 231 if (atomic_xchg(&lock->count, -1) == 1)
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232 break;
233
234 /*
235 * got a signal? (This code gets eliminated in the
236 * TASK_UNINTERRUPTIBLE case.)
237 */
6ad36762 238 if (unlikely(signal_pending_state(state, task))) {
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239 mutex_remove_waiter(lock, &waiter,
240 task_thread_info(task));
e4564f79 241 mutex_release(&lock->dep_map, 1, ip);
1fb00c6c 242 spin_unlock_mutex(&lock->wait_lock, flags);
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243
244 debug_mutex_free_waiter(&waiter);
41719b03 245 preempt_enable();
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246 return -EINTR;
247 }
248 __set_task_state(task, state);
249
250 /* didnt get the lock, go to sleep: */
1fb00c6c 251 spin_unlock_mutex(&lock->wait_lock, flags);
41719b03 252 __schedule();
1fb00c6c 253 spin_lock_mutex(&lock->wait_lock, flags);
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254 }
255
4fe87745 256done:
c7e78cff 257 lock_acquired(&lock->dep_map, ip);
6053ee3b 258 /* got the lock - rejoice! */
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259 mutex_remove_waiter(lock, &waiter, current_thread_info());
260 mutex_set_owner(lock);
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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
1fb00c6c 266 spin_unlock_mutex(&lock->wait_lock, flags);
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267
268 debug_mutex_free_waiter(&waiter);
41719b03 269 preempt_enable();
6053ee3b 270
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271 return 0;
272}
273
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274#ifdef CONFIG_DEBUG_LOCK_ALLOC
275void __sched
276mutex_lock_nested(struct mutex *lock, unsigned int subclass)
277{
278 might_sleep();
e4564f79 279 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_);
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280}
281
282EXPORT_SYMBOL_GPL(mutex_lock_nested);
d63a5a74 283
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284int __sched
285mutex_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}
290EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
291
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292int __sched
293mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
294{
295 might_sleep();
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296 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
297 subclass, _RET_IP_);
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298}
299
300EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
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301#endif
302
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303/*
304 * Release the lock, slowpath:
305 */
7ad5b3a5 306static inline void
ef5d4707 307__mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
6053ee3b 308{
02706647 309 struct mutex *lock = container_of(lock_count, struct mutex, count);
1fb00c6c 310 unsigned long flags;
6053ee3b 311
1fb00c6c 312 spin_lock_mutex(&lock->wait_lock, flags);
ef5d4707 313 mutex_release(&lock->dep_map, nested, _RET_IP_);
9a11b49a 314 debug_mutex_unlock(lock);
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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
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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
1fb00c6c 335 spin_unlock_mutex(&lock->wait_lock, flags);
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336}
337
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338/*
339 * Release the lock, slowpath:
340 */
7918baa5 341static __used noinline void
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342__mutex_unlock_slowpath(atomic_t *lock_count)
343{
ef5d4707 344 __mutex_unlock_common_slowpath(lock_count, 1);
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345}
346
e4564f79 347#ifndef CONFIG_DEBUG_LOCK_ALLOC
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348/*
349 * Here come the less common (and hence less performance-critical) APIs:
350 * mutex_lock_interruptible() and mutex_trylock().
351 */
7ad5b3a5 352static noinline int __sched
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353__mutex_lock_killable_slowpath(atomic_t *lock_count);
354
7ad5b3a5 355static noinline int __sched
9a11b49a 356__mutex_lock_interruptible_slowpath(atomic_t *lock_count);
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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 */
7ad5b3a5 369int __sched mutex_lock_interruptible(struct mutex *lock)
6053ee3b 370{
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371 int ret;
372
c544bdb1 373 might_sleep();
0d66bf6d 374 ret = __mutex_fastpath_lock_retval
6053ee3b 375 (&lock->count, __mutex_lock_interruptible_slowpath);
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376 if (!ret)
377 mutex_set_owner(lock);
378
379 return ret;
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380}
381
382EXPORT_SYMBOL(mutex_lock_interruptible);
383
7ad5b3a5 384int __sched mutex_lock_killable(struct mutex *lock)
ad776537 385{
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386 int ret;
387
ad776537 388 might_sleep();
0d66bf6d 389 ret = __mutex_fastpath_lock_retval
ad776537 390 (&lock->count, __mutex_lock_killable_slowpath);
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391 if (!ret)
392 mutex_set_owner(lock);
393
394 return ret;
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395}
396EXPORT_SYMBOL(mutex_lock_killable);
397
7918baa5 398static __used noinline void __sched
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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
7ad5b3a5 406static noinline int __sched
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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
7ad5b3a5 414static noinline int __sched
9a11b49a 415__mutex_lock_interruptible_slowpath(atomic_t *lock_count)
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416{
417 struct mutex *lock = container_of(lock_count, struct mutex, count);
418
e4564f79 419 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_);
6053ee3b 420}
e4564f79 421#endif
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422
423/*
424 * Spinlock based trylock, we take the spinlock and check whether we
425 * can get the lock:
426 */
427static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
428{
429 struct mutex *lock = container_of(lock_count, struct mutex, count);
1fb00c6c 430 unsigned long flags;
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431 int prev;
432
1fb00c6c 433 spin_lock_mutex(&lock->wait_lock, flags);
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434
435 prev = atomic_xchg(&lock->count, -1);
ef5d4707 436 if (likely(prev == 1)) {
0d66bf6d 437 mutex_set_owner(lock);
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438 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
439 }
0d66bf6d 440
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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
1fb00c6c 445 spin_unlock_mutex(&lock->wait_lock, flags);
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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 */
7ad5b3a5 464int __sched mutex_trylock(struct mutex *lock)
6053ee3b 465{
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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;
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473}
474
475EXPORT_SYMBOL(mutex_trylock);