Subversion Repositories test_project

/*

 * 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 fastcall 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 fastcall __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 void fastcall noinline __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 fastcall __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(state == TASK_INTERRUPTIBLE &&

                                                signal_pending(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_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 fastcall 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 fastcall 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 int fastcall noinline __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 fastcall __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);

static void fastcall noinline __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 int fastcall noinline __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 fastcall __sched mutex_trylock(struct mutex *lock)

{

        return __mutex_fastpath_trylock(&lock->count,

                                        __mutex_trylock_slowpath);

}

EXPORT_SYMBOL(mutex_trylock);