1/* kernel/rwsem.c: R/W semaphores, public implementation
  2 *
  3 * Written by David Howells (dhowells@redhat.com).
  4 * Derived from asm-i386/semaphore.h
  5 */
  6
  7#include <linux/types.h>
  8#include <linux/kernel.h>
  9#include <linux/sched.h>
 10#include <linux/export.h>
 11#include <linux/rwsem.h>
 12
 13#include <linux/atomic.h>
 14
 15/*
 16 * lock for reading
 17 */
 18void __sched down_read(struct rw_semaphore *sem)
 19{
 20	might_sleep();
 21	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
 22
 23	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 24}
 25
 26EXPORT_SYMBOL(down_read);
 27
 28/*
 29 * trylock for reading -- returns 1 if successful, 0 if contention
 30 */
 31int down_read_trylock(struct rw_semaphore *sem)
 32{
 33	int ret = __down_read_trylock(sem);
 34
 35	if (ret == 1)
 36		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
 37	return ret;
 38}
 39
 40EXPORT_SYMBOL(down_read_trylock);
 41
 42/*
 43 * lock for writing
 44 */
 45void __sched down_write(struct rw_semaphore *sem)
 46{
 47	might_sleep();
 48	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
 49
 50	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 51}
 52
 53EXPORT_SYMBOL(down_write);
 54
 55/*
 56 * trylock for writing -- returns 1 if successful, 0 if contention
 57 */
 58int down_write_trylock(struct rw_semaphore *sem)
 59{
 60	int ret = __down_write_trylock(sem);
 61
 62	if (ret == 1)
 63		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
 64	return ret;
 65}
 66
 67EXPORT_SYMBOL(down_write_trylock);
 68
 69/*
 70 * release a read lock
 71 */
 72void up_read(struct rw_semaphore *sem)
 73{
 74	rwsem_release(&sem->dep_map, 1, _RET_IP_);
 75
 76	__up_read(sem);
 77}
 78
 79EXPORT_SYMBOL(up_read);
 80
 81/*
 82 * release a write lock
 83 */
 84void up_write(struct rw_semaphore *sem)
 85{
 86	rwsem_release(&sem->dep_map, 1, _RET_IP_);
 87
 88	__up_write(sem);
 89}
 90
 91EXPORT_SYMBOL(up_write);
 92
 93/*
 94 * downgrade write lock to read lock
 95 */
 96void downgrade_write(struct rw_semaphore *sem)
 97{
 98	/*
 99	 * lockdep: a downgraded write will live on as a write
100	 * dependency.
101	 */
102	__downgrade_write(sem);
103}
104
105EXPORT_SYMBOL(downgrade_write);
106
107#ifdef CONFIG_DEBUG_LOCK_ALLOC
108
109void down_read_nested(struct rw_semaphore *sem, int subclass)
110{
111	might_sleep();
112	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
113
114	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
115}
116
117EXPORT_SYMBOL(down_read_nested);
118
119void down_write_nested(struct rw_semaphore *sem, int subclass)
120{
121	might_sleep();
122	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
123
124	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
125}
126
127EXPORT_SYMBOL(down_write_nested);
128
129#endif
130
131