4 * Mutexes: blocking mutual exclusion locks
6 * Started by Ingo Molnar:
8 * Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
10 * Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
11 * David Howells for suggestions and improvements.
13 * Also see Documentation/mutex-design.txt.
15 #include <linux/mutex.h>
16 #include <linux/sched.h>
17 #include <linux/module.h>
18 #include <linux/spinlock.h>
19 #include <linux/interrupt.h>
20 #include <linux/debug_locks.h>
23 * In the DEBUG case we are using the "NULL fastpath" for mutexes,
24 * which forces all calls into the slowpath:
26 #ifdef CONFIG_DEBUG_MUTEXES
27 # include "mutex-debug.h"
28 # include <asm-generic/mutex-null.h>
31 # include <asm/mutex.h>
35 * mutex_init - initialize the mutex
36 * @lock: the mutex to be initialized
38 * Initialize the mutex to unlocked state.
40 * It is not allowed to initialize an already locked mutex.
43 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
45 atomic_set(&lock->count, 1);
46 spin_lock_init(&lock->wait_lock);
47 INIT_LIST_HEAD(&lock->wait_list);
49 debug_mutex_init(lock, name, key);
52 EXPORT_SYMBOL(__mutex_init);
54 #ifndef CONFIG_DEBUG_LOCK_ALLOC
56 * We split the mutex lock/unlock logic into separate fastpath and
57 * slowpath functions, to reduce the register pressure on the fastpath.
58 * We also put the fastpath first in the kernel image, to make sure the
59 * branch is predicted by the CPU as default-untaken.
61 static void noinline __sched
62 __mutex_lock_slowpath(atomic_t *lock_count);
65 * mutex_lock - acquire the mutex
66 * @lock: the mutex to be acquired
68 * Lock the mutex exclusively for this task. If the mutex is not
69 * available right now, it will sleep until it can get it.
71 * The mutex must later on be released by the same task that
72 * acquired it. Recursive locking is not allowed. The task
73 * may not exit without first unlocking the mutex. Also, kernel
74 * memory where the mutex resides mutex must not be freed with
75 * the mutex still locked. The mutex must first be initialized
76 * (or statically defined) before it can be locked. memset()-ing
77 * the mutex to 0 is not allowed.
79 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
80 * checks that will enforce the restrictions and will also do
81 * deadlock debugging. )
83 * This function is similar to (but not equivalent to) down().
85 void inline __sched mutex_lock(struct mutex *lock)
89 * The locking fastpath is the 1->0 transition from
90 * 'unlocked' into 'locked' state.
92 __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
95 EXPORT_SYMBOL(mutex_lock);
98 static noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
101 * mutex_unlock - release the mutex
102 * @lock: the mutex to be released
104 * Unlock a mutex that has been locked by this task previously.
106 * This function must not be used in interrupt context. Unlocking
107 * of a not locked mutex is not allowed.
109 * This function is similar to (but not equivalent to) up().
111 void __sched mutex_unlock(struct mutex *lock)
114 * The unlocking fastpath is the 0->1 transition from 'locked'
115 * into 'unlocked' state:
117 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
120 EXPORT_SYMBOL(mutex_unlock);
123 * Lock a mutex (possibly interruptible), slowpath:
125 static inline int __sched
126 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
129 struct task_struct *task = current;
130 struct mutex_waiter waiter;
131 unsigned int old_val;
134 spin_lock_mutex(&lock->wait_lock, flags);
136 debug_mutex_lock_common(lock, &waiter);
137 mutex_acquire(&lock->dep_map, subclass, 0, ip);
138 debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
140 /* add waiting tasks to the end of the waitqueue (FIFO): */
141 list_add_tail(&waiter.list, &lock->wait_list);
144 old_val = atomic_xchg(&lock->count, -1);
148 lock_contended(&lock->dep_map, ip);
152 * Lets try to take the lock again - this is needed even if
153 * we get here for the first time (shortly after failing to
154 * acquire the lock), to make sure that we get a wakeup once
155 * it's unlocked. Later on, if we sleep, this is the
156 * operation that gives us the lock. We xchg it to -1, so
157 * that when we release the lock, we properly wake up the
160 old_val = atomic_xchg(&lock->count, -1);
165 * got a signal? (This code gets eliminated in the
166 * TASK_UNINTERRUPTIBLE case.)
168 if (unlikely(signal_pending_state(state, task))) {
169 mutex_remove_waiter(lock, &waiter,
170 task_thread_info(task));
171 mutex_release(&lock->dep_map, 1, ip);
172 spin_unlock_mutex(&lock->wait_lock, flags);
174 debug_mutex_free_waiter(&waiter);
177 __set_task_state(task, state);
179 /* didnt get the lock, go to sleep: */
180 spin_unlock_mutex(&lock->wait_lock, flags);
182 spin_lock_mutex(&lock->wait_lock, flags);
186 lock_acquired(&lock->dep_map);
187 /* got the lock - rejoice! */
188 mutex_remove_waiter(lock, &waiter, task_thread_info(task));
189 debug_mutex_set_owner(lock, task_thread_info(task));
191 /* set it to 0 if there are no waiters left: */
192 if (likely(list_empty(&lock->wait_list)))
193 atomic_set(&lock->count, 0);
195 spin_unlock_mutex(&lock->wait_lock, flags);
197 debug_mutex_free_waiter(&waiter);
202 #ifdef CONFIG_DEBUG_LOCK_ALLOC
204 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
207 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_);
210 EXPORT_SYMBOL_GPL(mutex_lock_nested);
213 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
216 return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_);
218 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
221 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
224 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_);
227 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
231 * Release the lock, slowpath:
234 __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
236 struct mutex *lock = container_of(lock_count, struct mutex, count);
239 spin_lock_mutex(&lock->wait_lock, flags);
240 mutex_release(&lock->dep_map, nested, _RET_IP_);
241 debug_mutex_unlock(lock);
244 * some architectures leave the lock unlocked in the fastpath failure
245 * case, others need to leave it locked. In the later case we have to
248 if (__mutex_slowpath_needs_to_unlock())
249 atomic_set(&lock->count, 1);
251 if (!list_empty(&lock->wait_list)) {
252 /* get the first entry from the wait-list: */
253 struct mutex_waiter *waiter =
254 list_entry(lock->wait_list.next,
255 struct mutex_waiter, list);
257 debug_mutex_wake_waiter(lock, waiter);
259 wake_up_process(waiter->task);
262 debug_mutex_clear_owner(lock);
264 spin_unlock_mutex(&lock->wait_lock, flags);
268 * Release the lock, slowpath:
271 __mutex_unlock_slowpath(atomic_t *lock_count)
273 __mutex_unlock_common_slowpath(lock_count, 1);
276 #ifndef CONFIG_DEBUG_LOCK_ALLOC
278 * Here come the less common (and hence less performance-critical) APIs:
279 * mutex_lock_interruptible() and mutex_trylock().
281 static noinline int __sched
282 __mutex_lock_killable_slowpath(atomic_t *lock_count);
284 static noinline int __sched
285 __mutex_lock_interruptible_slowpath(atomic_t *lock_count);
288 * mutex_lock_interruptible - acquire the mutex, interruptable
289 * @lock: the mutex to be acquired
291 * Lock the mutex like mutex_lock(), and return 0 if the mutex has
292 * been acquired or sleep until the mutex becomes available. If a
293 * signal arrives while waiting for the lock then this function
296 * This function is similar to (but not equivalent to) down_interruptible().
298 int __sched mutex_lock_interruptible(struct mutex *lock)
301 return __mutex_fastpath_lock_retval
302 (&lock->count, __mutex_lock_interruptible_slowpath);
305 EXPORT_SYMBOL(mutex_lock_interruptible);
307 int __sched mutex_lock_killable(struct mutex *lock)
310 return __mutex_fastpath_lock_retval
311 (&lock->count, __mutex_lock_killable_slowpath);
313 EXPORT_SYMBOL(mutex_lock_killable);
315 static noinline void __sched
316 __mutex_lock_slowpath(atomic_t *lock_count)
318 struct mutex *lock = container_of(lock_count, struct mutex, count);
320 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_);
323 static noinline int __sched
324 __mutex_lock_killable_slowpath(atomic_t *lock_count)
326 struct mutex *lock = container_of(lock_count, struct mutex, count);
328 return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_);
331 static noinline int __sched
332 __mutex_lock_interruptible_slowpath(atomic_t *lock_count)
334 struct mutex *lock = container_of(lock_count, struct mutex, count);
336 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_);
341 * Spinlock based trylock, we take the spinlock and check whether we
344 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
346 struct mutex *lock = container_of(lock_count, struct mutex, count);
350 spin_lock_mutex(&lock->wait_lock, flags);
352 prev = atomic_xchg(&lock->count, -1);
353 if (likely(prev == 1)) {
354 debug_mutex_set_owner(lock, current_thread_info());
355 mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
357 /* Set it back to 0 if there are no waiters: */
358 if (likely(list_empty(&lock->wait_list)))
359 atomic_set(&lock->count, 0);
361 spin_unlock_mutex(&lock->wait_lock, flags);
367 * mutex_trylock - try acquire the mutex, without waiting
368 * @lock: the mutex to be acquired
370 * Try to acquire the mutex atomically. Returns 1 if the mutex
371 * has been acquired successfully, and 0 on contention.
373 * NOTE: this function follows the spin_trylock() convention, so
374 * it is negated to the down_trylock() return values! Be careful
375 * about this when converting semaphore users to mutexes.
377 * This function must not be used in interrupt context. The
378 * mutex must be released by the same task that acquired it.
380 int __sched mutex_trylock(struct mutex *lock)
382 return __mutex_fastpath_trylock(&lock->count,
383 __mutex_trylock_slowpath);
386 EXPORT_SYMBOL(mutex_trylock);