2 * Mutexes: blocking mutual exclusion locks
4 * started by Ingo Molnar:
6 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
8 * This file contains the main data structure and API definitions.
10 #ifndef __LINUX_MUTEX_H
11 #define __LINUX_MUTEX_H
13 #include <asm/current.h>
14 #include <linux/list.h>
15 #include <linux/spinlock_types.h>
16 #include <linux/linkage.h>
17 #include <linux/lockdep.h>
19 #include <linux/atomic.h>
22 * Simple, straightforward mutexes with strict semantics:
24 * - only one task can hold the mutex at a time
25 * - only the owner can unlock the mutex
26 * - multiple unlocks are not permitted
27 * - recursive locking is not permitted
28 * - a mutex object must be initialized via the API
29 * - a mutex object must not be initialized via memset or copying
30 * - task may not exit with mutex held
31 * - memory areas where held locks reside must not be freed
32 * - held mutexes must not be reinitialized
33 * - mutexes may not be used in hardware or software interrupt
34 * contexts such as tasklets and timers
36 * These semantics are fully enforced when DEBUG_MUTEXES is
37 * enabled. Furthermore, besides enforcing the above rules, the mutex
38 * debugging code also implements a number of additional features
39 * that make lock debugging easier and faster:
41 * - uses symbolic names of mutexes, whenever they are printed in debug output
42 * - point-of-acquire tracking, symbolic lookup of function names
43 * - list of all locks held in the system, printout of them
45 * - detects self-recursing locks and prints out all relevant info
46 * - detects multi-task circular deadlocks and prints out all affected
47 * locks and tasks (and only those tasks)
50 /* 1: unlocked, 0: locked, negative: locked, possible waiters */
53 struct list_head wait_list
;
54 #if defined(CONFIG_DEBUG_MUTEXES) || defined(CONFIG_SMP)
55 struct task_struct
*owner
;
57 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
58 void *spin_mlock
; /* Spinner MCS lock */
60 #ifdef CONFIG_DEBUG_MUTEXES
64 #ifdef CONFIG_DEBUG_LOCK_ALLOC
65 struct lockdep_map dep_map
;
70 * This is the control structure for tasks blocked on mutex,
71 * which resides on the blocked task's kernel stack:
74 struct list_head list
;
75 struct task_struct
*task
;
76 #ifdef CONFIG_DEBUG_MUTEXES
83 struct lock_class_key acquire_key
;
84 struct lock_class_key mutex_key
;
85 const char *acquire_name
;
86 const char *mutex_name
;
89 struct ww_acquire_ctx
{
90 struct task_struct
*task
;
93 #ifdef CONFIG_DEBUG_MUTEXES
94 unsigned done_acquire
;
95 struct ww_class
*ww_class
;
96 struct ww_mutex
*contending_lock
;
98 #ifdef CONFIG_DEBUG_LOCK_ALLOC
99 struct lockdep_map dep_map
;
101 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
102 unsigned deadlock_inject_interval
;
103 unsigned deadlock_inject_countdown
;
109 struct ww_acquire_ctx
*ctx
;
110 #ifdef CONFIG_DEBUG_MUTEXES
111 struct ww_class
*ww_class
;
115 #ifdef CONFIG_DEBUG_MUTEXES
116 # include <linux/mutex-debug.h>
118 # define __DEBUG_MUTEX_INITIALIZER(lockname)
120 * mutex_init - initialize the mutex
121 * @mutex: the mutex to be initialized
123 * Initialize the mutex to unlocked state.
125 * It is not allowed to initialize an already locked mutex.
127 # define mutex_init(mutex) \
129 static struct lock_class_key __key; \
131 __mutex_init((mutex), #mutex, &__key); \
133 static inline void mutex_destroy(struct mutex
*lock
) {}
136 #ifdef CONFIG_DEBUG_LOCK_ALLOC
137 # define __DEP_MAP_MUTEX_INITIALIZER(lockname) \
138 , .dep_map = { .name = #lockname }
139 # define __WW_CLASS_MUTEX_INITIALIZER(lockname, ww_class) \
140 , .ww_class = &ww_class
142 # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
143 # define __WW_CLASS_MUTEX_INITIALIZER(lockname, ww_class)
146 #define __MUTEX_INITIALIZER(lockname) \
147 { .count = ATOMIC_INIT(1) \
148 , .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
149 , .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
150 __DEBUG_MUTEX_INITIALIZER(lockname) \
151 __DEP_MAP_MUTEX_INITIALIZER(lockname) }
153 #define __WW_CLASS_INITIALIZER(ww_class) \
154 { .stamp = ATOMIC_LONG_INIT(0) \
155 , .acquire_name = #ww_class "_acquire" \
156 , .mutex_name = #ww_class "_mutex" }
158 #define __WW_MUTEX_INITIALIZER(lockname, class) \
159 { .base = { \__MUTEX_INITIALIZER(lockname) } \
160 __WW_CLASS_MUTEX_INITIALIZER(lockname, class) }
162 #define DEFINE_MUTEX(mutexname) \
163 struct mutex mutexname = __MUTEX_INITIALIZER(mutexname)
165 #define DEFINE_WW_CLASS(classname) \
166 struct ww_class classname = __WW_CLASS_INITIALIZER(classname)
168 #define DEFINE_WW_MUTEX(mutexname, ww_class) \
169 struct ww_mutex mutexname = __WW_MUTEX_INITIALIZER(mutexname, ww_class)
172 extern void __mutex_init(struct mutex
*lock
, const char *name
,
173 struct lock_class_key
*key
);
176 * ww_mutex_init - initialize the w/w mutex
177 * @lock: the mutex to be initialized
178 * @ww_class: the w/w class the mutex should belong to
180 * Initialize the w/w mutex to unlocked state and associate it with the given
183 * It is not allowed to initialize an already locked mutex.
185 static inline void ww_mutex_init(struct ww_mutex
*lock
,
186 struct ww_class
*ww_class
)
188 __mutex_init(&lock
->base
, ww_class
->mutex_name
, &ww_class
->mutex_key
);
190 #ifdef CONFIG_DEBUG_MUTEXES
191 lock
->ww_class
= ww_class
;
196 * mutex_is_locked - is the mutex locked
197 * @lock: the mutex to be queried
199 * Returns 1 if the mutex is locked, 0 if unlocked.
201 static inline int mutex_is_locked(struct mutex
*lock
)
203 return atomic_read(&lock
->count
) != 1;
207 * See kernel/mutex.c for detailed documentation of these APIs.
208 * Also see Documentation/mutex-design.txt.
210 #ifdef CONFIG_DEBUG_LOCK_ALLOC
211 extern void mutex_lock_nested(struct mutex
*lock
, unsigned int subclass
);
212 extern void _mutex_lock_nest_lock(struct mutex
*lock
, struct lockdep_map
*nest_lock
);
214 extern int __must_check
mutex_lock_interruptible_nested(struct mutex
*lock
,
215 unsigned int subclass
);
216 extern int __must_check
mutex_lock_killable_nested(struct mutex
*lock
,
217 unsigned int subclass
);
219 #define mutex_lock(lock) mutex_lock_nested(lock, 0)
220 #define mutex_lock_interruptible(lock) mutex_lock_interruptible_nested(lock, 0)
221 #define mutex_lock_killable(lock) mutex_lock_killable_nested(lock, 0)
223 #define mutex_lock_nest_lock(lock, nest_lock) \
225 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
226 _mutex_lock_nest_lock(lock, &(nest_lock)->dep_map); \
230 extern void mutex_lock(struct mutex
*lock
);
231 extern int __must_check
mutex_lock_interruptible(struct mutex
*lock
);
232 extern int __must_check
mutex_lock_killable(struct mutex
*lock
);
234 # define mutex_lock_nested(lock, subclass) mutex_lock(lock)
235 # define mutex_lock_interruptible_nested(lock, subclass) mutex_lock_interruptible(lock)
236 # define mutex_lock_killable_nested(lock, subclass) mutex_lock_killable(lock)
237 # define mutex_lock_nest_lock(lock, nest_lock) mutex_lock(lock)
241 * NOTE: mutex_trylock() follows the spin_trylock() convention,
242 * not the down_trylock() convention!
244 * Returns 1 if the mutex has been acquired successfully, and 0 on contention.
246 extern int mutex_trylock(struct mutex
*lock
);
247 extern void mutex_unlock(struct mutex
*lock
);
250 * ww_acquire_init - initialize a w/w acquire context
251 * @ctx: w/w acquire context to initialize
252 * @ww_class: w/w class of the context
254 * Initializes an context to acquire multiple mutexes of the given w/w class.
256 * Context-based w/w mutex acquiring can be done in any order whatsoever within
257 * a given lock class. Deadlocks will be detected and handled with the
260 * Mixing of context-based w/w mutex acquiring and single w/w mutex locking can
261 * result in undetected deadlocks and is so forbidden. Mixing different contexts
262 * for the same w/w class when acquiring mutexes can also result in undetected
263 * deadlocks, and is hence also forbidden. Both types of abuse will be caught by
264 * enabling CONFIG_PROVE_LOCKING.
266 * Nesting of acquire contexts for _different_ w/w classes is possible, subject
267 * to the usual locking rules between different lock classes.
269 * An acquire context must be released with ww_acquire_fini by the same task
270 * before the memory is freed. It is recommended to allocate the context itself
273 static inline void ww_acquire_init(struct ww_acquire_ctx
*ctx
,
274 struct ww_class
*ww_class
)
277 ctx
->stamp
= atomic_long_inc_return(&ww_class
->stamp
);
279 #ifdef CONFIG_DEBUG_MUTEXES
280 ctx
->ww_class
= ww_class
;
281 ctx
->done_acquire
= 0;
282 ctx
->contending_lock
= NULL
;
284 #ifdef CONFIG_DEBUG_LOCK_ALLOC
285 debug_check_no_locks_freed((void *)ctx
, sizeof(*ctx
));
286 lockdep_init_map(&ctx
->dep_map
, ww_class
->acquire_name
,
287 &ww_class
->acquire_key
, 0);
288 mutex_acquire(&ctx
->dep_map
, 0, 0, _RET_IP_
);
290 #ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
291 ctx
->deadlock_inject_interval
= 1;
292 ctx
->deadlock_inject_countdown
= ctx
->stamp
& 0xf;
297 * ww_acquire_done - marks the end of the acquire phase
298 * @ctx: the acquire context
300 * Marks the end of the acquire phase, any further w/w mutex lock calls using
301 * this context are forbidden.
303 * Calling this function is optional, it is just useful to document w/w mutex
304 * code and clearly designated the acquire phase from actually using the locked
307 static inline void ww_acquire_done(struct ww_acquire_ctx
*ctx
)
309 #ifdef CONFIG_DEBUG_MUTEXES
310 lockdep_assert_held(ctx
);
312 DEBUG_LOCKS_WARN_ON(ctx
->done_acquire
);
313 ctx
->done_acquire
= 1;
318 * ww_acquire_fini - releases a w/w acquire context
319 * @ctx: the acquire context to free
321 * Releases a w/w acquire context. This must be called _after_ all acquired w/w
322 * mutexes have been released with ww_mutex_unlock.
324 static inline void ww_acquire_fini(struct ww_acquire_ctx
*ctx
)
326 #ifdef CONFIG_DEBUG_MUTEXES
327 mutex_release(&ctx
->dep_map
, 0, _THIS_IP_
);
329 DEBUG_LOCKS_WARN_ON(ctx
->acquired
);
330 if (!config_enabled(CONFIG_PROVE_LOCKING
))
332 * lockdep will normally handle this,
333 * but fail without anyway
335 ctx
->done_acquire
= 1;
337 if (!config_enabled(CONFIG_DEBUG_LOCK_ALLOC
))
338 /* ensure ww_acquire_fini will still fail if called twice */
343 extern int __must_check
__ww_mutex_lock(struct ww_mutex
*lock
,
344 struct ww_acquire_ctx
*ctx
);
345 extern int __must_check
__ww_mutex_lock_interruptible(struct ww_mutex
*lock
,
346 struct ww_acquire_ctx
*ctx
);
349 * ww_mutex_lock - acquire the w/w mutex
350 * @lock: the mutex to be acquired
351 * @ctx: w/w acquire context, or NULL to acquire only a single lock.
353 * Lock the w/w mutex exclusively for this task.
355 * Deadlocks within a given w/w class of locks are detected and handled with the
356 * wait/wound algorithm. If the lock isn't immediately avaiable this function
357 * will either sleep until it is (wait case). Or it selects the current context
358 * for backing off by returning -EDEADLK (wound case). Trying to acquire the
359 * same lock with the same context twice is also detected and signalled by
360 * returning -EALREADY. Returns 0 if the mutex was successfully acquired.
362 * In the wound case the caller must release all currently held w/w mutexes for
363 * the given context and then wait for this contending lock to be available by
364 * calling ww_mutex_lock_slow. Alternatively callers can opt to not acquire this
365 * lock and proceed with trying to acquire further w/w mutexes (e.g. when
366 * scanning through lru lists trying to free resources).
368 * The mutex must later on be released by the same task that
369 * acquired it. The task may not exit without first unlocking the mutex. Also,
370 * kernel memory where the mutex resides must not be freed with the mutex still
371 * locked. The mutex must first be initialized (or statically defined) before it
372 * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
373 * of the same w/w lock class as was used to initialize the acquire context.
375 * A mutex acquired with this function must be released with ww_mutex_unlock.
377 static inline int ww_mutex_lock(struct ww_mutex
*lock
, struct ww_acquire_ctx
*ctx
)
380 return __ww_mutex_lock(lock
, ctx
);
382 mutex_lock(&lock
->base
);
388 * ww_mutex_lock_interruptible - acquire the w/w mutex, interruptible
389 * @lock: the mutex to be acquired
390 * @ctx: w/w acquire context
392 * Lock the w/w mutex exclusively for this task.
394 * Deadlocks within a given w/w class of locks are detected and handled with the
395 * wait/wound algorithm. If the lock isn't immediately avaiable this function
396 * will either sleep until it is (wait case). Or it selects the current context
397 * for backing off by returning -EDEADLK (wound case). Trying to acquire the
398 * same lock with the same context twice is also detected and signalled by
399 * returning -EALREADY. Returns 0 if the mutex was successfully acquired. If a
400 * signal arrives while waiting for the lock then this function returns -EINTR.
402 * In the wound case the caller must release all currently held w/w mutexes for
403 * the given context and then wait for this contending lock to be available by
404 * calling ww_mutex_lock_slow_interruptible. Alternatively callers can opt to
405 * not acquire this lock and proceed with trying to acquire further w/w mutexes
406 * (e.g. when scanning through lru lists trying to free resources).
408 * The mutex must later on be released by the same task that
409 * acquired it. The task may not exit without first unlocking the mutex. Also,
410 * kernel memory where the mutex resides must not be freed with the mutex still
411 * locked. The mutex must first be initialized (or statically defined) before it
412 * can be locked. memset()-ing the mutex to 0 is not allowed. The mutex must be
413 * of the same w/w lock class as was used to initialize the acquire context.
415 * A mutex acquired with this function must be released with ww_mutex_unlock.
417 static inline int __must_check
ww_mutex_lock_interruptible(struct ww_mutex
*lock
,
418 struct ww_acquire_ctx
*ctx
)
421 return __ww_mutex_lock_interruptible(lock
, ctx
);
423 return mutex_lock_interruptible(&lock
->base
);
427 * ww_mutex_lock_slow - slowpath acquiring of the w/w mutex
428 * @lock: the mutex to be acquired
429 * @ctx: w/w acquire context
431 * Acquires a w/w mutex with the given context after a wound case. This function
432 * will sleep until the lock becomes available.
434 * The caller must have released all w/w mutexes already acquired with the
435 * context and then call this function on the contended lock.
437 * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
438 * needs with ww_mutex_lock. Note that the -EALREADY return code from
439 * ww_mutex_lock can be used to avoid locking this contended mutex twice.
441 * It is forbidden to call this function with any other w/w mutexes associated
442 * with the context held. It is forbidden to call this on anything else than the
445 * Note that the slowpath lock acquiring can also be done by calling
446 * ww_mutex_lock directly. This function here is simply to help w/w mutex
447 * locking code readability by clearly denoting the slowpath.
450 ww_mutex_lock_slow(struct ww_mutex
*lock
, struct ww_acquire_ctx
*ctx
)
453 #ifdef CONFIG_DEBUG_MUTEXES
454 DEBUG_LOCKS_WARN_ON(!ctx
->contending_lock
);
456 ret
= ww_mutex_lock(lock
, ctx
);
461 * ww_mutex_lock_slow_interruptible - slowpath acquiring of the w/w mutex,
463 * @lock: the mutex to be acquired
464 * @ctx: w/w acquire context
466 * Acquires a w/w mutex with the given context after a wound case. This function
467 * will sleep until the lock becomes available and returns 0 when the lock has
468 * been acquired. If a signal arrives while waiting for the lock then this
469 * function returns -EINTR.
471 * The caller must have released all w/w mutexes already acquired with the
472 * context and then call this function on the contended lock.
474 * Afterwards the caller may continue to (re)acquire the other w/w mutexes it
475 * needs with ww_mutex_lock. Note that the -EALREADY return code from
476 * ww_mutex_lock can be used to avoid locking this contended mutex twice.
478 * It is forbidden to call this function with any other w/w mutexes associated
479 * with the given context held. It is forbidden to call this on anything else
480 * than the contending mutex.
482 * Note that the slowpath lock acquiring can also be done by calling
483 * ww_mutex_lock_interruptible directly. This function here is simply to help
484 * w/w mutex locking code readability by clearly denoting the slowpath.
486 static inline int __must_check
487 ww_mutex_lock_slow_interruptible(struct ww_mutex
*lock
,
488 struct ww_acquire_ctx
*ctx
)
490 #ifdef CONFIG_DEBUG_MUTEXES
491 DEBUG_LOCKS_WARN_ON(!ctx
->contending_lock
);
493 return ww_mutex_lock_interruptible(lock
, ctx
);
496 extern void ww_mutex_unlock(struct ww_mutex
*lock
);
499 * ww_mutex_trylock - tries to acquire the w/w mutex without acquire context
500 * @lock: mutex to lock
502 * Trylocks a mutex without acquire context, so no deadlock detection is
503 * possible. Returns 1 if the mutex has been acquired successfully, 0 otherwise.
505 static inline int __must_check
ww_mutex_trylock(struct ww_mutex
*lock
)
507 return mutex_trylock(&lock
->base
);
511 * ww_mutex_destroy - mark a w/w mutex unusable
512 * @lock: the mutex to be destroyed
514 * This function marks the mutex uninitialized, and any subsequent
515 * use of the mutex is forbidden. The mutex must not be locked when
516 * this function is called.
518 static inline void ww_mutex_destroy(struct ww_mutex
*lock
)
520 mutex_destroy(&lock
->base
);
524 * ww_mutex_is_locked - is the w/w mutex locked
525 * @lock: the mutex to be queried
527 * Returns 1 if the mutex is locked, 0 if unlocked.
529 static inline bool ww_mutex_is_locked(struct ww_mutex
*lock
)
531 return mutex_is_locked(&lock
->base
);
534 extern int atomic_dec_and_mutex_lock(atomic_t
*cnt
, struct mutex
*lock
);
536 #ifndef CONFIG_HAVE_ARCH_MUTEX_CPU_RELAX
537 #define arch_mutex_cpu_relax() cpu_relax()