| /* |
| * 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. |
| * |
| * Also see Documentation/mutex-design.txt. |
| */ |
| #include <linux/mutex.h> |
| #include <linux/sched.h> |
| #include <linux/module.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 |
| |
| /*** |
| * mutex_init - initialize the mutex |
| * @lock: the mutex to be initialized |
| * |
| * Initialize the mutex to unlocked state. |
| * |
| * It is not allowed to initialize an already locked mutex. |
| */ |
| 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); |
| |
| 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 void noinline __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 inline __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); |
| } |
| |
| EXPORT_SYMBOL(mutex_lock); |
| #endif |
| |
| static 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: |
| */ |
| __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, |
| unsigned long ip) |
| { |
| struct task_struct *task = current; |
| struct mutex_waiter waiter; |
| unsigned int old_val; |
| unsigned long flags; |
| |
| 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) |
| 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: |
| */ |
| old_val = atomic_xchg(&lock->count, -1); |
| if (old_val == 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); |
| return -EINTR; |
| } |
| __set_task_state(task, state); |
| |
| /* didnt get the lock, go to sleep: */ |
| spin_unlock_mutex(&lock->wait_lock, flags); |
| schedule(); |
| spin_lock_mutex(&lock->wait_lock, flags); |
| } |
| |
| done: |
| lock_acquired(&lock->dep_map); |
| /* got the lock - rejoice! */ |
| mutex_remove_waiter(lock, &waiter, task_thread_info(task)); |
| debug_mutex_set_owner(lock, task_thread_info(task)); |
| |
| /* 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); |
| |
| return 0; |
| } |
| |
| #ifdef CONFIG_DEBUG_LOCK_ALLOC |
| void __sched |
| mutex_lock_nested(struct mutex *lock, unsigned int subclass) |
| { |
| might_sleep(); |
| __mutex_lock_common(lock, TASK_UNINTERRUPTIBLE, subclass, _RET_IP_); |
| } |
| |
| EXPORT_SYMBOL_GPL(mutex_lock_nested); |
| |
| int __sched |
| mutex_lock_killable_nested(struct mutex *lock, unsigned int subclass) |
| { |
| might_sleep(); |
| return __mutex_lock_common(lock, TASK_KILLABLE, subclass, _RET_IP_); |
| } |
| EXPORT_SYMBOL_GPL(mutex_lock_killable_nested); |
| |
| int __sched |
| mutex_lock_interruptible_nested(struct mutex *lock, unsigned int subclass) |
| { |
| might_sleep(); |
| return __mutex_lock_common(lock, TASK_INTERRUPTIBLE, subclass, _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); |
| } |
| |
| debug_mutex_clear_owner(lock); |
| |
| spin_unlock_mutex(&lock->wait_lock, flags); |
| } |
| |
| /* |
| * Release the lock, slowpath: |
| */ |
| static 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, interruptable |
| * @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) |
| { |
| might_sleep(); |
| return __mutex_fastpath_lock_retval |
| (&lock->count, __mutex_lock_interruptible_slowpath); |
| } |
| |
| EXPORT_SYMBOL(mutex_lock_interruptible); |
| |
| int __sched mutex_lock_killable(struct mutex *lock) |
| { |
| might_sleep(); |
| return __mutex_fastpath_lock_retval |
| (&lock->count, __mutex_lock_killable_slowpath); |
| } |
| EXPORT_SYMBOL(mutex_lock_killable); |
| |
| static 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, _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, _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, _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)) { |
| debug_mutex_set_owner(lock, current_thread_info()); |
| 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 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 to 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) |
| { |
| return __mutex_fastpath_trylock(&lock->count, |
| __mutex_trylock_slowpath); |
| } |
| |
| EXPORT_SYMBOL(mutex_trylock); |