* Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
* David Howells for suggestions and improvements.
*
+ * - Adaptive spinning for mutexes by Peter Zijlstra. (Ported to mainline
+ * from the -rt tree, where it was originally implemented for rtmutexes
+ * by Steven Rostedt, based on work by Gregory Haskins, Peter Morreale
+ * and Sven Dietrich.
+ *
* Also see Documentation/mutex-design.txt.
*/
#include <linux/mutex.h>
atomic_set(&lock->count, 1);
spin_lock_init(&lock->wait_lock);
INIT_LIST_HEAD(&lock->wait_list);
+ mutex_clear_owner(lock);
debug_mutex_init(lock, name, key);
}
*
* This function is similar to (but not equivalent to) down().
*/
-void inline __sched mutex_lock(struct mutex *lock)
+void __sched mutex_lock(struct mutex *lock)
{
might_sleep();
/*
* 'unlocked' into 'locked' state.
*/
__mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
+ mutex_set_owner(lock);
}
EXPORT_SYMBOL(mutex_lock);
* The unlocking fastpath is the 0->1 transition from 'locked'
* into 'unlocked' state:
*/
+#ifndef CONFIG_DEBUG_MUTEXES
+ /*
+ * When debugging is enabled we must not clear the owner before time,
+ * the slow path will always be taken, and that clears the owner field
+ * after verifying that it was indeed current.
+ */
+ mutex_clear_owner(lock);
+#endif
__mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
}
{
struct task_struct *task = current;
struct mutex_waiter waiter;
- unsigned int old_val;
unsigned long flags;
+ preempt_disable();
+ mutex_acquire(&lock->dep_map, subclass, 0, ip);
+
+#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
+ /*
+ * Optimistic spinning.
+ *
+ * We try to spin for acquisition when we find that there are no
+ * pending waiters and the lock owner is currently running on a
+ * (different) CPU.
+ *
+ * The rationale is that if the lock owner is running, it is likely to
+ * release the lock soon.
+ *
+ * Since this needs the lock owner, and this mutex implementation
+ * doesn't track the owner atomically in the lock field, we need to
+ * track it non-atomically.
+ *
+ * We can't do this for DEBUG_MUTEXES because that relies on wait_lock
+ * to serialize everything.
+ */
+
+ for (;;) {
+ struct thread_info *owner;
+
+ /*
+ * If we own the BKL, then don't spin. The owner of
+ * the mutex might be waiting on us to release the BKL.
+ */
+ if (unlikely(current->lock_depth >= 0))
+ break;
+
+ /*
+ * If there's an owner, wait for it to either
+ * release the lock or go to sleep.
+ */
+ owner = ACCESS_ONCE(lock->owner);
+ if (owner && !mutex_spin_on_owner(lock, owner))
+ break;
+
+ if (atomic_cmpxchg(&lock->count, 1, 0) == 1) {
+ lock_acquired(&lock->dep_map, ip);
+ mutex_set_owner(lock);
+ preempt_enable();
+ return 0;
+ }
+
+ /*
+ * When there's no owner, we might have preempted between the
+ * owner acquiring the lock and setting the owner field. If
+ * we're an RT task that will live-lock because we won't let
+ * the owner complete.
+ */
+ if (!owner && (need_resched() || rt_task(task)))
+ break;
+
+ /*
+ * The cpu_relax() call is a compiler barrier which forces
+ * everything in this loop to be re-loaded. We don't need
+ * memory barriers as we'll eventually observe the right
+ * values at the cost of a few extra spins.
+ */
+ cpu_relax();
+ }
+#endif
spin_lock_mutex(&lock->wait_lock, flags);
debug_mutex_lock_common(lock, &waiter);
- mutex_acquire(&lock->dep_map, subclass, 0, ip);
debug_mutex_add_waiter(lock, &waiter, task_thread_info(task));
/* add waiting tasks to the end of the waitqueue (FIFO): */
list_add_tail(&waiter.list, &lock->wait_list);
waiter.task = task;
- old_val = atomic_xchg(&lock->count, -1);
- if (old_val == 1)
+ if (atomic_xchg(&lock->count, -1) == 1)
goto done;
lock_contended(&lock->dep_map, ip);
* that when we release the lock, we properly wake up the
* other waiters:
*/
- old_val = atomic_xchg(&lock->count, -1);
- if (old_val == 1)
+ if (atomic_xchg(&lock->count, -1) == 1)
break;
/*
spin_unlock_mutex(&lock->wait_lock, flags);
debug_mutex_free_waiter(&waiter);
+ preempt_enable();
return -EINTR;
}
__set_task_state(task, state);
/* didnt get the lock, go to sleep: */
spin_unlock_mutex(&lock->wait_lock, flags);
+ preempt_enable_no_resched();
schedule();
+ preempt_disable();
spin_lock_mutex(&lock->wait_lock, flags);
}
done:
lock_acquired(&lock->dep_map, ip);
/* got the lock - rejoice! */
- mutex_remove_waiter(lock, &waiter, task_thread_info(task));
- debug_mutex_set_owner(lock, task_thread_info(task));
+ mutex_remove_waiter(lock, &waiter, current_thread_info());
+ mutex_set_owner(lock);
/* set it to 0 if there are no waiters left: */
if (likely(list_empty(&lock->wait_list)))
spin_unlock_mutex(&lock->wait_lock, flags);
debug_mutex_free_waiter(&waiter);
+ preempt_enable();
return 0;
}
mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass)
{
might_sleep();
- return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _RET_IP_);
+ return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,
+ subclass, _RET_IP_);
}
EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);
wake_up_process(waiter->task);
}
- debug_mutex_clear_owner(lock);
-
spin_unlock_mutex(&lock->wait_lock, flags);
}
*/
int __sched mutex_lock_interruptible(struct mutex *lock)
{
+ int ret;
+
might_sleep();
- return __mutex_fastpath_lock_retval
+ ret = __mutex_fastpath_lock_retval
(&lock->count, __mutex_lock_interruptible_slowpath);
+ if (!ret)
+ mutex_set_owner(lock);
+
+ return ret;
}
EXPORT_SYMBOL(mutex_lock_interruptible);
int __sched mutex_lock_killable(struct mutex *lock)
{
+ int ret;
+
might_sleep();
- return __mutex_fastpath_lock_retval
+ ret = __mutex_fastpath_lock_retval
(&lock->count, __mutex_lock_killable_slowpath);
+ if (!ret)
+ mutex_set_owner(lock);
+
+ return ret;
}
EXPORT_SYMBOL(mutex_lock_killable);
prev = atomic_xchg(&lock->count, -1);
if (likely(prev == 1)) {
- debug_mutex_set_owner(lock, current_thread_info());
+ mutex_set_owner(lock);
mutex_acquire(&lock->dep_map, 0, 1, _RET_IP_);
}
+
/* Set it back to 0 if there are no waiters: */
if (likely(list_empty(&lock->wait_list)))
atomic_set(&lock->count, 0);
*/
int __sched mutex_trylock(struct mutex *lock)
{
- return __mutex_fastpath_trylock(&lock->count,
- __mutex_trylock_slowpath);
-}
+ int ret;
+ ret = __mutex_fastpath_trylock(&lock->count, __mutex_trylock_slowpath);
+ if (ret)
+ mutex_set_owner(lock);
+
+ return ret;
+}
EXPORT_SYMBOL(mutex_trylock);
+
+/**
+ * atomic_dec_and_mutex_lock - return holding mutex if we dec to 0
+ * @cnt: the atomic which we are to dec
+ * @lock: the mutex to return holding if we dec to 0
+ *
+ * return true and hold lock if we dec to 0, return false otherwise
+ */
+int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock)
+{
+ /* dec if we can't possibly hit 0 */
+ if (atomic_add_unless(cnt, -1, 1))
+ return 0;
+ /* we might hit 0, so take the lock */
+ mutex_lock(lock);
+ if (!atomic_dec_and_test(cnt)) {
+ /* when we actually did the dec, we didn't hit 0 */
+ mutex_unlock(lock);
+ return 0;
+ }
+ /* we hit 0, and we hold the lock */
+ return 1;
+}
+EXPORT_SYMBOL(atomic_dec_and_mutex_lock);
git://ftp.safe.ca / safe / jmp / linux-2.6 / blobdiff