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#include <linux/atomic.h>
 13
 14#include "rwsem.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	rwsem_set_owner(sem);
 53}
 54
 55EXPORT_SYMBOL(down_write);
 56
 57/*
 58 * trylock for writing -- returns 1 if successful, 0 if contention
 59 */
 60int down_write_trylock(struct rw_semaphore *sem)
 61{
 62	int ret = __down_write_trylock(sem);
 63
 64	if (ret == 1) {
 65		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
 66		rwsem_set_owner(sem);
 67	}
 68
 69	return ret;
 70}
 71
 72EXPORT_SYMBOL(down_write_trylock);
 73
 74/*
 75 * release a read lock
 76 */
 77void up_read(struct rw_semaphore *sem)
 78{
 79	rwsem_release(&sem->dep_map, 1, _RET_IP_);
 80
 81	__up_read(sem);
 82}
 83
 84EXPORT_SYMBOL(up_read);
 85
 86/*
 87 * release a write lock
 88 */
 89void up_write(struct rw_semaphore *sem)
 90{
 91	rwsem_release(&sem->dep_map, 1, _RET_IP_);
 92
 93	rwsem_clear_owner(sem);
 94	__up_write(sem);
 95}
 96
 97EXPORT_SYMBOL(up_write);
 98
 99/*
100 * downgrade write lock to read lock
101 */
102void downgrade_write(struct rw_semaphore *sem)
103{
104	/*
105	 * lockdep: a downgraded write will live on as a write
106	 * dependency.
107	 */
108	rwsem_clear_owner(sem);
109	__downgrade_write(sem);
110}
111
112EXPORT_SYMBOL(downgrade_write);
113
114#ifdef CONFIG_DEBUG_LOCK_ALLOC
115
116void down_read_nested(struct rw_semaphore *sem, int subclass)
117{
118	might_sleep();
119	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
120
121	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
122}
123
124EXPORT_SYMBOL(down_read_nested);
125
126void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
127{
128	might_sleep();
129	rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
130
131	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
132	rwsem_set_owner(sem);
133}
134
135EXPORT_SYMBOL(_down_write_nest_lock);
136
137void down_read_non_owner(struct rw_semaphore *sem)
138{
139	might_sleep();
140
141	__down_read(sem);
142}
143
144EXPORT_SYMBOL(down_read_non_owner);
145
146void down_write_nested(struct rw_semaphore *sem, int subclass)
147{
148	might_sleep();
149	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
150
151	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
152	rwsem_set_owner(sem);
153}
154
155EXPORT_SYMBOL(down_write_nested);
156
157void up_read_non_owner(struct rw_semaphore *sem)
158{
159	__up_read(sem);
160}
161
162EXPORT_SYMBOL(up_read_non_owner);
163
164#endif
165
166