rwsem.c

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/* kernel/rwsem.c: R/W semaphores, public implementation
 *
 * Written by David Howells (dhowells@redhat.com).
 * Derived from asm-i386/semaphore.h
 */

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/export.h>
#include <linux/rwsem.h>

#include <linux/atomic.h>

/*
 * lock for reading
 */
void __sched down_read(struct rw_semaphore *sem)
{
    might_sleep();
    rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);

    LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
}

EXPORT_SYMBOL(down_read);

/*
 * trylock for reading -- returns 1 if successful, 0 if contention
 */
int down_read_trylock(struct rw_semaphore *sem)
{
    int ret = __down_read_trylock(sem);

    if (ret == 1)
        rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
    return ret;
}

EXPORT_SYMBOL(down_read_trylock);

/*
 * lock for writing
 */
void __sched down_write(struct rw_semaphore *sem)
{
    might_sleep();
    rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);

    LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}

EXPORT_SYMBOL(down_write);

/*
 * trylock for writing -- returns 1 if successful, 0 if contention
 */
int down_write_trylock(struct rw_semaphore *sem)
{
    int ret = __down_write_trylock(sem);

    if (ret == 1)
        rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
    return ret;
}

EXPORT_SYMBOL(down_write_trylock);

/*
 * release a read lock
 */
void up_read(struct rw_semaphore *sem)
{
    rwsem_release(&sem->dep_map, 1, _RET_IP_);

    __up_read(sem);
}

EXPORT_SYMBOL(up_read);

/*
 * release a write lock
 */
void up_write(struct rw_semaphore *sem)
{
    rwsem_release(&sem->dep_map, 1, _RET_IP_);

    __up_write(sem);
}

EXPORT_SYMBOL(up_write);

/*
 * downgrade write lock to read lock
 */
void downgrade_write(struct rw_semaphore *sem)
{
    /*
     * lockdep: a downgraded write will live on as a write
     * dependency.
     */
    __downgrade_write(sem);
}

EXPORT_SYMBOL(downgrade_write);

#ifdef CONFIG_DEBUG_LOCK_ALLOC

void down_read_nested(struct rw_semaphore *sem, int subclass)
{
    might_sleep();
    rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);

    LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
}

EXPORT_SYMBOL(down_read_nested);

void down_write_nested(struct rw_semaphore *sem, int subclass)
{
    might_sleep();
    rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);

    LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
}

EXPORT_SYMBOL(down_write_nested);

#endif