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/module.h>
 11#include <linux/rwsem.h>
 12
 13#include <asm/system.h>
 14#include <linux/atomic.h>
 15
 16/*
 17 * lock for reading
 18 */
 19void __sched down_read(struct rw_semaphore *sem)
 20{
 21	might_sleep();
 22	rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
 23
 24	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 25}
 26
 27EXPORT_SYMBOL(down_read);
 28
 29/*
 30 * trylock for reading -- returns 1 if successful, 0 if contention
 31 */
 32int down_read_trylock(struct rw_semaphore *sem)
 33{
 34	int ret = __down_read_trylock(sem);
 35
 36	if (ret == 1)
 37		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
 38	return ret;
 39}
 40
 41EXPORT_SYMBOL(down_read_trylock);
 42
 43/*
 44 * lock for writing
 45 */
 46void __sched down_write(struct rw_semaphore *sem)
 47{
 48	might_sleep();
 49	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
 50
 51	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 52}
 53
 54EXPORT_SYMBOL(down_write);
 55
 56/*
 57 * trylock for writing -- returns 1 if successful, 0 if contention
 58 */
 59int down_write_trylock(struct rw_semaphore *sem)
 60{
 61	int ret = __down_write_trylock(sem);
 62
 63	if (ret == 1)
 64		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
 65	return ret;
 66}
 67
 68EXPORT_SYMBOL(down_write_trylock);
 69
 70/*
 71 * release a read lock
 72 */
 73void up_read(struct rw_semaphore *sem)
 74{
 75	rwsem_release(&sem->dep_map, 1, _RET_IP_);
 76
 77	__up_read(sem);
 78}
 79
 80EXPORT_SYMBOL(up_read);
 81
 82/*
 83 * release a write lock
 84 */
 85void up_write(struct rw_semaphore *sem)
 86{
 87	rwsem_release(&sem->dep_map, 1, _RET_IP_);
 88
 89	__up_write(sem);
 90}
 91
 92EXPORT_SYMBOL(up_write);
 93
 94/*
 95 * downgrade write lock to read lock
 96 */
 97void downgrade_write(struct rw_semaphore *sem)
 98{
 99	/*
100	 * lockdep: a downgraded write will live on as a write
101	 * dependency.
102	 */
103	__downgrade_write(sem);
104}
105
106EXPORT_SYMBOL(downgrade_write);
107
108#ifdef CONFIG_DEBUG_LOCK_ALLOC
109
110void down_read_nested(struct rw_semaphore *sem, int subclass)
111{
112	might_sleep();
113	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
114
115	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
116}
117
118EXPORT_SYMBOL(down_read_nested);
119
120void down_write_nested(struct rw_semaphore *sem, int subclass)
121{
122	might_sleep();
123	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
124
125	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
126}
127
128EXPORT_SYMBOL(down_write_nested);
129
130#endif
131
132