/* * kernel/mutex.c * * Mutexes: blocking mutual exclusion locks * * Started by Ingo Molnar: * *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com> * * 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>#include <linux/sched.h>#include <linux/export.h>#include <linux/spinlock.h>#include <linux/interrupt.h>#include <linux/debug_locks.h> /* * In the DEBUG case we are using the "NULL fastpath" for mutexes, * which forces all calls into the slowpath: */#ifdef CONFIG_DEBUG_MUTEXES# include "mutex-debug.h"# include <asm-generic/mutex-null.h>#else# include "mutex.h"# include <asm/mutex.h>#endif void__mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key){	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);} EXPORT_SYMBOL(__mutex_init); #ifndef CONFIG_DEBUG_LOCK_ALLOC/* * We split the mutex lock/unlock logic into separate fastpath and * slowpath functions, to reduce the register pressure on the fastpath. * We also put the fastpath first in the kernel image, to make sure the * branch is predicted by the CPU as default-untaken. */static __used noinline void __sched__mutex_lock_slowpath(atomic_t *lock_count); /** * mutex_lock - acquire the mutex * @lock: the mutex to be acquired * * Lock the mutex exclusively for this task. If the mutex is not * available right now, it will sleep until it can get it. * * The mutex must later on be released by the same task that * acquired it. Recursive locking is not allowed. The task * may not exit without first unlocking the mutex. Also, kernel * memory where the mutex resides mutex must not be freed with * the mutex still locked. The mutex must first be initialized * (or statically defined) before it can be locked. memset()-ing * the mutex to 0 is not allowed. * * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging *   checks that will enforce the restrictions and will also do *   deadlock debugging. ) * * This function is similar to (but not equivalent to) down(). */void __sched mutex_lock(struct mutex *lock){	might_sleep();	/*	 * The locking fastpath is the 1->0 transition from	 * 'unlocked' into 'locked' state.	 */	__mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);	mutex_set_owner(lock);} EXPORT_SYMBOL(mutex_lock);#endif static __used noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count); /** * mutex_unlock - release the mutex * @lock: the mutex to be released * * Unlock a mutex that has been locked by this task previously. * * This function must not be used in interrupt context. Unlocking * of a not locked mutex is not allowed. * * This function is similar to (but not equivalent to) up(). */void __sched mutex_unlock(struct 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);} EXPORT_SYMBOL(mutex_unlock); /* * Lock a mutex (possibly interruptible), slowpath: */static inline int __sched__mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,		    struct lockdep_map *nest_lock, unsigned long ip){	struct task_struct *task = current;	struct mutex_waiter waiter;	unsigned long flags; 	preempt_disable();	mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, 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 task_struct *owner; 		/*		 * 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.		 */		arch_mutex_cpu_relax();	}#endif	spin_lock_mutex(&lock->wait_lock, flags); 	debug_mutex_lock_common(lock, &waiter);	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; 	if (atomic_xchg(&lock->count, -1) == 1)		goto done; 	lock_contended(&lock->dep_map, ip); 	for (;;) {		/*		 * Lets try to take the lock again - this is needed even if		 * we get here for the first time (shortly after failing to		 * acquire the lock), to make sure that we get a wakeup once		 * it's unlocked. Later on, if we sleep, this is the		 * operation that gives us the lock. We xchg it to -1, so		 * that when we release the lock, we properly wake up the		 * other waiters:		 */		if (atomic_xchg(&lock->count, -1) == 1)			break; 		/*		 * got a signal? (This code gets eliminated in the		 * TASK_UNINTERRUPTIBLE case.)		 */		if (unlikely(signal_pending_state(state, task))) {			mutex_remove_waiter(lock, &waiter,					    task_thread_info(task));			mutex_release(&lock->dep_map, 1, ip);			spin_unlock_mutex(&lock->wait_lock, flags); 			debug_mutex_free_waiter(&waiter);			preempt_enable();			return -EINTR;		}		__set_task_state(task, state); 		/* didn't get the lock, go to sleep: */		spin_unlock_mutex(&lock->wait_lock, flags);		schedule_preempt_disabled();		spin_lock_mutex(&lock->wait_lock, flags);	} done:	lock_acquired(&lock->dep_map, ip);	/* got the lock - rejoice! */	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)))		atomic_set(&lock->count, 0); 	spin_unlock_mutex(&lock->wait_lock, flags); 	debug_mutex_free_waiter(&waiter);	preempt_enable(); 	return 0;} #ifdef CONFIG_DEBUG_LOCK_ALLOCvoid __schedmutex_lock_nested(struct mutex *lock, unsigned int subclass){	might_sleep();	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, NULL, _RET_IP_);} EXPORT_SYMBOL_GPL(mutex_lock_nested); void __sched_mutex_lock_nest_lock(struct mutex *lock, struct lockdep_map *nest){	might_sleep();	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, nest, _RET_IP_);} EXPORT_SYMBOL_GPL(_mutex_lock_nest_lock); int __schedmutex_lock_killable_nested(struct mutex *lock, unsigned int subclass){	might_sleep();	return __mutex_lock_common(lock, TASK_KILLABLE, subclass, NULL, _RET_IP_);}EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); int __schedmutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass){	might_sleep();	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE,				   subclass, NULL, _RET_IP_);} EXPORT_SYMBOL_GPL(mutex_lock_interruptible_nested);#endif /* * Release the lock, slowpath: */static inline void__mutex_unlock_common_slowpath(atomic_t *lock_count, int nested){	struct mutex *lock = container_of(lock_count, struct mutex, count);	unsigned long flags; 	spin_lock_mutex(&lock->wait_lock, flags);	mutex_release(&lock->dep_map, nested, _RET_IP_);	debug_mutex_unlock(lock); 	/*	 * some architectures leave the lock unlocked in the fastpath failure	 * case, others need to leave it locked. In the later case we have to	 * unlock it here	 */	if (__mutex_slowpath_needs_to_unlock())		atomic_set(&lock->count, 1); 	if (!list_empty(&lock->wait_list)) {		/* get the first entry from the wait-list: */		struct mutex_waiter *waiter =				list_entry(lock->wait_list.next,					   struct mutex_waiter, list); 		debug_mutex_wake_waiter(lock, waiter); 		wake_up_process(waiter->task);	} 	spin_unlock_mutex(&lock->wait_lock, flags);} /* * Release the lock, slowpath: */static __used noinline void__mutex_unlock_slowpath(atomic_t *lock_count){	__mutex_unlock_common_slowpath(lock_count, 1);} #ifndef CONFIG_DEBUG_LOCK_ALLOC/* * Here come the less common (and hence less performance-critical) APIs: * mutex_lock_interruptible() and mutex_trylock(). */static noinline int __sched__mutex_lock_killable_slowpath(atomic_t *lock_count); static noinline int __sched__mutex_lock_interruptible_slowpath(atomic_t *lock_count); /** * mutex_lock_interruptible - acquire the mutex, interruptible * @lock: the mutex to be acquired * * Lock the mutex like mutex_lock(), and return 0 if the mutex has * been acquired or sleep until the mutex becomes available. If a * signal arrives while waiting for the lock then this function * returns -EINTR. * * This function is similar to (but not equivalent to) down_interruptible(). */int __sched mutex_lock_interruptible(struct mutex *lock){	int ret; 	might_sleep();	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();	ret = __mutex_fastpath_lock_retval			(&lock->count, __mutex_lock_killable_slowpath);	if (!ret)		mutex_set_owner(lock); 	return ret;}EXPORT_SYMBOL(mutex_lock_killable); static __used noinline void __sched__mutex_lock_slowpath(atomic_t *lock_count){	struct mutex *lock = container_of(lock_count, struct mutex, count); 	__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, 0, NULL, _RET_IP_);} static noinline int __sched__mutex_lock_killable_slowpath(atomic_t *lock_count){	struct mutex *lock = container_of(lock_count, struct mutex, count); 	return __mutex_lock_common(lock, TASK_KILLABLE, 0, NULL, _RET_IP_);} static noinline int __sched__mutex_lock_interruptible_slowpath(atomic_t *lock_count){	struct mutex *lock = container_of(lock_count, struct mutex, count); 	return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, 0, NULL, _RET_IP_);}#endif /* * Spinlock based trylock, we take the spinlock and check whether we * can get the lock: */static inline int __mutex_trylock_slowpath(atomic_t *lock_count){	struct mutex *lock = container_of(lock_count, struct mutex, count);	unsigned long flags;	int prev; 	spin_lock_mutex(&lock->wait_lock, flags); 	prev = atomic_xchg(&lock->count, -1);	if (likely(prev == 1)) {		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); 	spin_unlock_mutex(&lock->wait_lock, flags); 	return prev == 1;} /** * mutex_trylock - try to acquire the mutex, without waiting * @lock: the mutex to be acquired * * Try to acquire the mutex atomically. Returns 1 if the mutex * has been acquired successfully, and 0 on contention. * * NOTE: this function follows the spin_trylock() convention, so * it is negated from the down_trylock() return values! Be careful * about this when converting semaphore users to mutexes. * * This function must not be used in interrupt context. The * mutex must be released by the same task that acquired it. */int __sched mutex_trylock(struct mutex *lock){	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);