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Octocat-spinner-32-eaf2f5

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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/module.h>
#include <linux/rwsem.h>

#include <asm/system.h>
#include <asm/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_read_non_owner(struct rw_semaphore *sem)
{
might_sleep();

__down_read(sem);
}

EXPORT_SYMBOL(down_read_non_owner);

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);

void up_read_non_owner(struct rw_semaphore *sem)
{
__up_read(sem);
}

EXPORT_SYMBOL(up_read_non_owner);

#endif


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