inetpeer: Don't disable BH for initial fast RCU lookup.
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / mutex.c
bloba5889fb28ecff33eaf5fae64c9d2a50ca03cb2f7
1 /*
2 * kernel/mutex.c
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 * - 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.
18 * Also see Documentation/mutex-design.txt.
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>
28 * In the DEBUG case we are using the "NULL fastpath" for mutexes,
29 * which forces all calls into the slowpath:
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
39 void
40 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
42 atomic_set(&lock->count, 1);
43 spin_lock_init(&lock->wait_lock);
44 INIT_LIST_HEAD(&lock->wait_list);
45 mutex_clear_owner(lock);
47 debug_mutex_init(lock, name, key);
50 EXPORT_SYMBOL(__mutex_init);
52 #ifndef CONFIG_DEBUG_LOCK_ALLOC
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.
59 static __used noinline void __sched
60 __mutex_lock_slowpath(atomic_t *lock_count);
62 /**
63 * mutex_lock - acquire the mutex
64 * @lock: the mutex to be acquired
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.
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.
77 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
78 * checks that will enforce the restrictions and will also do
79 * deadlock debugging. )
81 * This function is similar to (but not equivalent to) down().
83 void __sched mutex_lock(struct mutex *lock)
85 might_sleep();
87 * The locking fastpath is the 1->0 transition from
88 * 'unlocked' into 'locked' state.
90 __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
91 mutex_set_owner(lock);
94 EXPORT_SYMBOL(mutex_lock);
95 #endif
97 static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
99 /**
100 * mutex_unlock - release the mutex
101 * @lock: the mutex to be released
103 * Unlock a mutex that has been locked by this task previously.
105 * This function must not be used in interrupt context. Unlocking
106 * of a not locked mutex is not allowed.
108 * This function is similar to (but not equivalent to) up().
110 void __sched mutex_unlock(struct mutex *lock)
113 * The unlocking fastpath is the 0->1 transition from 'locked'
114 * into 'unlocked' state:
116 #ifndef CONFIG_DEBUG_MUTEXES
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.
122 mutex_clear_owner(lock);
123 #endif
124 __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
127 EXPORT_SYMBOL(mutex_unlock);
130 * Lock a mutex (possibly interruptible), slowpath:
132 static inline int __sched
133 __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
134 unsigned long ip)
136 struct task_struct *task = current;
137 struct mutex_waiter waiter;
138 unsigned long flags;
140 preempt_disable();
141 mutex_acquire(&lock->dep_map, subclass, 0, ip);
143 #ifdef CONFIG_MUTEX_SPIN_ON_OWNER
145 * Optimistic spinning.
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.
151 * The rationale is that if the lock owner is running, it is likely to
152 * release the lock soon.
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.
158 * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
159 * to serialize everything.
162 for (;;) {
163 struct thread_info *owner;
166 * If we own the BKL, then don't spin. The owner of
167 * the mutex might be waiting on us to release the BKL.
169 if (unlikely(current->lock_depth >= 0))
170 break;
173 * If there's an owner, wait for it to either
174 * release the lock or go to sleep.
176 owner = ACCESS_ONCE(lock->owner);
177 if (owner && !mutex_spin_on_owner(lock, owner))
178 break;
180 if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {
181 lock_acquired(&lock->dep_map, ip);
182 mutex_set_owner(lock);
183 preempt_enable();
184 return 0;
188 * When there's no owner, we might have preempted between the
189 * owner acquiring the lock and setting the owner field. If
190 * we're an RT task that will live-lock because we won't let
191 * the owner complete.
193 if (!owner && (need_resched() || rt_task(task)))
194 break;
197 * The cpu_relax() call is a compiler barrier which forces
198 * everything in this loop to be re-loaded. We don't need
199 * memory barriers as we'll eventually observe the right
200 * values at the cost of a few extra spins.
202 arch_mutex_cpu_relax();
204 #endif
205 spin_lock_mutex(&lock->wait_lock, flags);
207 debug_mutex_lock_common(lock, &waiter);
208 debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
210 /* add waiting tasks to the end of the waitqueue (FIFO): */
211 list_add_tail(&waiter.list, &lock->wait_list);
212 waiter.task = task;
214 if (atomic_xchg(&lock->count, -1) == 1)
215 goto done;
217 lock_contended(&lock->dep_map, ip);
219 for (;;) {
221 * Lets try to take the lock again - this is needed even if
222 * we get here for the first time (shortly after failing to
223 * acquire the lock), to make sure that we get a wakeup once
224 * it's unlocked. Later on, if we sleep, this is the
225 * operation that gives us the lock. We xchg it to -1, so
226 * that when we release the lock, we properly wake up the
227 * other waiters:
229 if (atomic_xchg(&lock->count, -1) == 1)
230 break;
233 * got a signal? (This code gets eliminated in the
234 * TASK_UNINTERRUPTIBLE case.)
236 if (unlikely(signal_pending_state(state, task))) {
237 mutex_remove_waiter(lock, &waiter,
238 task_thread_info(task));
239 mutex_release(&lock->dep_map, 1, ip);
240 spin_unlock_mutex(&lock->wait_lock, flags);
242 debug_mutex_free_waiter(&waiter);
243 preempt_enable();
244 return -EINTR;
246 __set_task_state(task, state);
248 /* didnt get the lock, go to sleep: */
249 spin_unlock_mutex(&lock->wait_lock, flags);
250 preempt_enable_no_resched();
251 schedule();
252 preempt_disable();
253 spin_lock_mutex(&lock->wait_lock, flags);
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);
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);
266 spin_unlock_mutex(&lock->wait_lock, flags);
268 debug_mutex_free_waiter(&waiter);
269 preempt_enable();
271 return 0;
274 #ifdef CONFIG_DEBUG_LOCK_ALLOC
275 void __sched
276 mutex_lock_nested(struct mutex *lock, unsigned int subclass)
278 might_sleep();
279 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_);
282 EXPORT_SYMBOL_GPL(mutex_lock_nested);
284 int __sched
285 mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass)
287 might_sleep();
288 return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_);
290 EXPORT_SYMBOL_GPL(mutex_lock_killable_nested);
292 int __sched
293 mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
295 might_sleep();
296 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
297 subclass, _RET_IP_);
300 EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
301 #endif
304 * Release the lock, slowpath:
306 static inline void
307 __mutex_unlock_common_slowpath(atomic_t *lock_count, int nested)
309 struct mutex *lock = container_of(lock_count, struct mutex, count);
310 unsigned long flags;
312 spin_lock_mutex(&lock->wait_lock, flags);
313 mutex_release(&lock->dep_map, nested, _RET_IP_);
314 debug_mutex_unlock(lock);
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
321 if (__mutex_slowpath_needs_to_unlock())
322 atomic_set(&lock->count, 1);
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);
330 debug_mutex_wake_waiter(lock, waiter);
332 wake_up_process(waiter->task);
335 spin_unlock_mutex(&lock->wait_lock, flags);
339 * Release the lock, slowpath:
341 static __used noinline void
342 __mutex_unlock_slowpath(atomic_t *lock_count)
344 __mutex_unlock_common_slowpath(lock_count, 1);
347 #ifndef CONFIG_DEBUG_LOCK_ALLOC
349 * Here come the less common (and hence less performance-critical) APIs:
350 * mutex_lock_interruptible() and mutex_trylock().
352 static noinline int __sched
353 __mutex_lock_killable_slowpath(atomic_t *lock_count);
355 static noinline int __sched
356 __mutex_lock_interruptible_slowpath(atomic_t *lock_count);
359 * mutex_lock_interruptible - acquire the mutex, interruptible
360 * @lock: the mutex to be acquired
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.
367 * This function is similar to (but not equivalent to) down_interruptible().
369 int __sched mutex_lock_interruptible(struct mutex *lock)
371 int ret;
373 might_sleep();
374 ret = __mutex_fastpath_lock_retval
375 (&lock->count, __mutex_lock_interruptible_slowpath);
376 if (!ret)
377 mutex_set_owner(lock);
379 return ret;
382 EXPORT_SYMBOL(mutex_lock_interruptible);
384 int __sched mutex_lock_killable(struct mutex *lock)
386 int ret;
388 might_sleep();
389 ret = __mutex_fastpath_lock_retval
390 (&lock->count, __mutex_lock_killable_slowpath);
391 if (!ret)
392 mutex_set_owner(lock);
394 return ret;
396 EXPORT_SYMBOL(mutex_lock_killable);
398 static __used noinline void __sched
399 __mutex_lock_slowpath(atomic_t *lock_count)
401 struct mutex *lock = container_of(lock_count, struct mutex, count);
403 __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, _RET_IP_);
406 static noinline int __sched
407 __mutex_lock_killable_slowpath(atomic_t *lock_count)
409 struct mutex *lock = container_of(lock_count, struct mutex, count);
411 return __mutex_lock_common(lock, TASK_KILLABLE, 0, _RET_IP_);
414 static noinline int __sched
415 __mutex_lock_interruptible_slowpath(atomic_t *lock_count)
417 struct mutex *lock = container_of(lock_count, struct mutex, count);
419 return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, _RET_IP_);
421 #endif
424 * Spinlock based trylock, we take the spinlock and check whether we
425 * can get the lock:
427 static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
429 struct mutex *lock = container_of(lock_count, struct mutex, count);
430 unsigned long flags;
431 int prev;
433 spin_lock_mutex(&lock->wait_lock, flags);
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_);
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);
445 spin_unlock_mutex(&lock->wait_lock, flags);
447 return prev == 1;
451 * mutex_trylock - try to acquire the mutex, without waiting
452 * @lock: the mutex to be acquired
454 * Try to acquire the mutex atomically. Returns 1 if the mutex
455 * has been acquired successfully, and 0 on contention.
457 * NOTE: this function follows the spin_trylock() convention, so
458 * it is negated from the down_trylock() return values! Be careful
459 * about this when converting semaphore users to mutexes.
461 * This function must not be used in interrupt context. The
462 * mutex must be released by the same task that acquired it.
464 int __sched mutex_trylock(struct mutex *lock)
466 int ret;
468 ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
469 if (ret)
470 mutex_set_owner(lock);
472 return ret;
474 EXPORT_SYMBOL(mutex_trylock);
477 * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
478 * @cnt: the atomic which we are to dec
479 * @lock: the mutex to return holding if we dec to 0
481 * return true and hold lock if we dec to 0, return false otherwise
483 int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
485 /* dec if we can't possibly hit 0 */
486 if (atomic_add_unless(cnt, -1, 1))
487 return 0;
488 /* we might hit 0, so take the lock */
489 mutex_lock(lock);
490 if (!atomic_dec_and_test(cnt)) {
491 /* when we actually did the dec, we didn't hit 0 */
492 mutex_unlock(lock);
493 return 0;
495 /* we hit 0, and we hold the lock */
496 return 1;
498 EXPORT_SYMBOL(atomic_dec_and_mutex_lock);