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02706647a4
Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
316 lines
8.6 KiB
C
316 lines
8.6 KiB
C
/*
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* kernel/mutex.c
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*
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* Mutexes: blocking mutual exclusion locks
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*
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* Started by Ingo Molnar:
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*
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* Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
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*
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* Many thanks to Arjan van de Ven, Thomas Gleixner, Steven Rostedt and
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* David Howells for suggestions and improvements.
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*
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* Also see Documentation/mutex-design.txt.
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*/
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#include <linux/mutex.h>
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#include <linux/sched.h>
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#include <linux/module.h>
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#include <linux/spinlock.h>
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#include <linux/interrupt.h>
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/*
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* In the DEBUG case we are using the "NULL fastpath" for mutexes,
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* which forces all calls into the slowpath:
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*/
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#ifdef CONFIG_DEBUG_MUTEXES
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# include "mutex-debug.h"
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# include <asm-generic/mutex-null.h>
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#else
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# include "mutex.h"
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# include <asm/mutex.h>
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#endif
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/***
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* mutex_init - initialize the mutex
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* @lock: the mutex to be initialized
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*
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* Initialize the mutex to unlocked state.
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*
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* It is not allowed to initialize an already locked mutex.
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*/
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void fastcall __mutex_init(struct mutex *lock, const char *name)
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{
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atomic_set(&lock->count, 1);
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spin_lock_init(&lock->wait_lock);
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INIT_LIST_HEAD(&lock->wait_list);
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debug_mutex_init(lock, name);
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}
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EXPORT_SYMBOL(__mutex_init);
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/*
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* We split the mutex lock/unlock logic into separate fastpath and
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* slowpath functions, to reduce the register pressure on the fastpath.
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* We also put the fastpath first in the kernel image, to make sure the
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* branch is predicted by the CPU as default-untaken.
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*/
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static void fastcall noinline __sched
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__mutex_lock_slowpath(atomic_t *lock_count __IP_DECL__);
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/***
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* mutex_lock - acquire the mutex
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* @lock: the mutex to be acquired
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*
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* Lock the mutex exclusively for this task. If the mutex is not
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* available right now, it will sleep until it can get it.
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*
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* The mutex must later on be released by the same task that
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* acquired it. Recursive locking is not allowed. The task
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* may not exit without first unlocking the mutex. Also, kernel
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* memory where the mutex resides mutex must not be freed with
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* the mutex still locked. The mutex must first be initialized
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* (or statically defined) before it can be locked. memset()-ing
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* the mutex to 0 is not allowed.
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*
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* ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
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* checks that will enforce the restrictions and will also do
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* deadlock debugging. )
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*
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* This function is similar to (but not equivalent to) down().
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*/
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void fastcall __sched mutex_lock(struct mutex *lock)
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{
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might_sleep();
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/*
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* The locking fastpath is the 1->0 transition from
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* 'unlocked' into 'locked' state.
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*/
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__mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
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}
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EXPORT_SYMBOL(mutex_lock);
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static void fastcall noinline __sched
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__mutex_unlock_slowpath(atomic_t *lock_count __IP_DECL__);
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/***
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* mutex_unlock - release the mutex
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* @lock: the mutex to be released
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*
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* Unlock a mutex that has been locked by this task previously.
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*
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* This function must not be used in interrupt context. Unlocking
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* of a not locked mutex is not allowed.
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*
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* This function is similar to (but not equivalent to) up().
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*/
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void fastcall __sched mutex_unlock(struct mutex *lock)
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{
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/*
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* The unlocking fastpath is the 0->1 transition from 'locked'
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* into 'unlocked' state:
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*/
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__mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
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}
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EXPORT_SYMBOL(mutex_unlock);
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/*
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* Lock a mutex (possibly interruptible), slowpath:
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*/
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static inline int __sched
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__mutex_lock_common(struct mutex *lock, long state __IP_DECL__)
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{
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struct task_struct *task = current;
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struct mutex_waiter waiter;
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unsigned int old_val;
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debug_mutex_init_waiter(&waiter);
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spin_lock_mutex(&lock->wait_lock);
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debug_mutex_add_waiter(lock, &waiter, task->thread_info, ip);
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/* add waiting tasks to the end of the waitqueue (FIFO): */
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list_add_tail(&waiter.list, &lock->wait_list);
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waiter.task = task;
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for (;;) {
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/*
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* Lets try to take the lock again - this is needed even if
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* we get here for the first time (shortly after failing to
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* acquire the lock), to make sure that we get a wakeup once
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* it's unlocked. Later on, if we sleep, this is the
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* operation that gives us the lock. We xchg it to -1, so
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* that when we release the lock, we properly wake up the
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* other waiters:
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*/
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old_val = atomic_xchg(&lock->count, -1);
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if (old_val == 1)
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break;
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/*
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* got a signal? (This code gets eliminated in the
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* TASK_UNINTERRUPTIBLE case.)
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*/
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if (unlikely(state == TASK_INTERRUPTIBLE &&
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signal_pending(task))) {
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mutex_remove_waiter(lock, &waiter, task->thread_info);
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spin_unlock_mutex(&lock->wait_lock);
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debug_mutex_free_waiter(&waiter);
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return -EINTR;
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}
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__set_task_state(task, state);
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/* didnt get the lock, go to sleep: */
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spin_unlock_mutex(&lock->wait_lock);
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schedule();
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spin_lock_mutex(&lock->wait_lock);
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}
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/* got the lock - rejoice! */
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mutex_remove_waiter(lock, &waiter, task->thread_info);
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debug_mutex_set_owner(lock, task->thread_info __IP__);
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/* set it to 0 if there are no waiters left: */
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if (likely(list_empty(&lock->wait_list)))
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atomic_set(&lock->count, 0);
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spin_unlock_mutex(&lock->wait_lock);
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debug_mutex_free_waiter(&waiter);
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DEBUG_WARN_ON(list_empty(&lock->held_list));
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DEBUG_WARN_ON(lock->owner != task->thread_info);
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return 0;
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}
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static void fastcall noinline __sched
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__mutex_lock_slowpath(atomic_t *lock_count __IP_DECL__)
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{
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struct mutex *lock = container_of(lock_count, struct mutex, count);
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__mutex_lock_common(lock, TASK_UNINTERRUPTIBLE __IP__);
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}
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/*
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* Release the lock, slowpath:
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*/
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static fastcall noinline void
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__mutex_unlock_slowpath(atomic_t *lock_count __IP_DECL__)
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{
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struct mutex *lock = container_of(lock_count, struct mutex, count);
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DEBUG_WARN_ON(lock->owner != current_thread_info());
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spin_lock_mutex(&lock->wait_lock);
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/*
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* some architectures leave the lock unlocked in the fastpath failure
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* case, others need to leave it locked. In the later case we have to
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* unlock it here
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*/
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if (__mutex_slowpath_needs_to_unlock())
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atomic_set(&lock->count, 1);
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debug_mutex_unlock(lock);
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if (!list_empty(&lock->wait_list)) {
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/* get the first entry from the wait-list: */
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struct mutex_waiter *waiter =
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list_entry(lock->wait_list.next,
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struct mutex_waiter, list);
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debug_mutex_wake_waiter(lock, waiter);
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wake_up_process(waiter->task);
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}
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debug_mutex_clear_owner(lock);
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spin_unlock_mutex(&lock->wait_lock);
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}
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/*
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* Here come the less common (and hence less performance-critical) APIs:
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* mutex_lock_interruptible() and mutex_trylock().
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*/
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static int fastcall noinline __sched
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__mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__);
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/***
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* mutex_lock_interruptible - acquire the mutex, interruptable
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* @lock: the mutex to be acquired
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*
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* Lock the mutex like mutex_lock(), and return 0 if the mutex has
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* been acquired or sleep until the mutex becomes available. If a
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* signal arrives while waiting for the lock then this function
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* returns -EINTR.
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*
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* This function is similar to (but not equivalent to) down_interruptible().
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*/
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int fastcall __sched mutex_lock_interruptible(struct mutex *lock)
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{
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might_sleep();
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return __mutex_fastpath_lock_retval
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(&lock->count, __mutex_lock_interruptible_slowpath);
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}
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EXPORT_SYMBOL(mutex_lock_interruptible);
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static int fastcall noinline __sched
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__mutex_lock_interruptible_slowpath(atomic_t *lock_count __IP_DECL__)
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{
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struct mutex *lock = container_of(lock_count, struct mutex, count);
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return __mutex_lock_common(lock, TASK_INTERRUPTIBLE __IP__);
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}
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/*
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* Spinlock based trylock, we take the spinlock and check whether we
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* can get the lock:
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*/
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static inline int __mutex_trylock_slowpath(atomic_t *lock_count)
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{
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struct mutex *lock = container_of(lock_count, struct mutex, count);
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int prev;
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spin_lock_mutex(&lock->wait_lock);
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prev = atomic_xchg(&lock->count, -1);
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if (likely(prev == 1))
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debug_mutex_set_owner(lock, current_thread_info() __RET_IP__);
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/* Set it back to 0 if there are no waiters: */
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if (likely(list_empty(&lock->wait_list)))
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atomic_set(&lock->count, 0);
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spin_unlock_mutex(&lock->wait_lock);
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return prev == 1;
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}
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/***
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* mutex_trylock - try acquire the mutex, without waiting
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* @lock: the mutex to be acquired
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*
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* Try to acquire the mutex atomically. Returns 1 if the mutex
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* has been acquired successfully, and 0 on contention.
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*
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* NOTE: this function follows the spin_trylock() convention, so
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* it is negated to the down_trylock() return values! Be careful
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* about this when converting semaphore users to mutexes.
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*
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* This function must not be used in interrupt context. The
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* mutex must be released by the same task that acquired it.
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*/
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int fastcall mutex_trylock(struct mutex *lock)
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{
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return __mutex_fastpath_trylock(&lock->count,
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__mutex_trylock_slowpath);
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}
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EXPORT_SYMBOL(mutex_trylock);
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