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	rwsem_set_reader_owned(sem);
 26}
 27
 28EXPORT_SYMBOL(down_read);
 29
 30/*
 31 * trylock for reading -- returns 1 if successful, 0 if contention
 32 */
 33int down_read_trylock(struct rw_semaphore *sem)
 34{
 35	int ret = __down_read_trylock(sem);
 36
 37	if (ret == 1) {
 38		rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
 39		rwsem_set_reader_owned(sem);
 40	}
 41	return ret;
 42}
 43
 44EXPORT_SYMBOL(down_read_trylock);
 45
 46/*
 47 * lock for writing
 48 */
 49void __sched down_write(struct rw_semaphore *sem)
 50{
 51	might_sleep();
 52	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
 53
 54	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 55	rwsem_set_owner(sem);
 56}
 57
 58EXPORT_SYMBOL(down_write);
 59
 60/*
 61 * lock for writing
 62 */
 63int __sched down_write_killable(struct rw_semaphore *sem)
 64{
 65	might_sleep();
 66	rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
 67
 68	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) {
 69		rwsem_release(&sem->dep_map, 1, _RET_IP_);
 70		return -EINTR;
 71	}
 72
 73	rwsem_set_owner(sem);
 74	return 0;
 75}
 76
 77EXPORT_SYMBOL(down_write_killable);
 78
 79/*
 80 * trylock for writing -- returns 1 if successful, 0 if contention
 81 */
 82int down_write_trylock(struct rw_semaphore *sem)
 83{
 84	int ret = __down_write_trylock(sem);
 85
 86	if (ret == 1) {
 87		rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
 88		rwsem_set_owner(sem);
 89	}
 90
 91	return ret;
 92}
 93
 94EXPORT_SYMBOL(down_write_trylock);
 95
 96/*
 97 * release a read lock
 98 */
 99void up_read(struct rw_semaphore *sem)
100{
101	rwsem_release(&sem->dep_map, 1, _RET_IP_);
102
103	__up_read(sem);
104}
105
106EXPORT_SYMBOL(up_read);
107
108/*
109 * release a write lock
110 */
111void up_write(struct rw_semaphore *sem)
112{
113	rwsem_release(&sem->dep_map, 1, _RET_IP_);
114
115	rwsem_clear_owner(sem);
116	__up_write(sem);
117}
118
119EXPORT_SYMBOL(up_write);
120
121/*
122 * downgrade write lock to read lock
123 */
124void downgrade_write(struct rw_semaphore *sem)
125{
126	/*
127	 * lockdep: a downgraded write will live on as a write
128	 * dependency.
129	 */
130	rwsem_set_reader_owned(sem);
131	__downgrade_write(sem);
132}
133
134EXPORT_SYMBOL(downgrade_write);
135
136#ifdef CONFIG_DEBUG_LOCK_ALLOC
137
138void down_read_nested(struct rw_semaphore *sem, int subclass)
139{
140	might_sleep();
141	rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
142
143	LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
144	rwsem_set_reader_owned(sem);
145}
146
147EXPORT_SYMBOL(down_read_nested);
148
149void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
150{
151	might_sleep();
152	rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
153
154	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
155	rwsem_set_owner(sem);
156}
157
158EXPORT_SYMBOL(_down_write_nest_lock);
159
160void down_read_non_owner(struct rw_semaphore *sem)
161{
162	might_sleep();
163
164	__down_read(sem);
165}
166
167EXPORT_SYMBOL(down_read_non_owner);
168
169void down_write_nested(struct rw_semaphore *sem, int subclass)
170{
171	might_sleep();
172	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
173
174	LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
175	rwsem_set_owner(sem);
176}
177
178EXPORT_SYMBOL(down_write_nested);
179
180int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
181{
182	might_sleep();
183	rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
184
185	if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) {
186		rwsem_release(&sem->dep_map, 1, _RET_IP_);
187		return -EINTR;
188	}
189
190	rwsem_set_owner(sem);
191	return 0;
192}
193
194EXPORT_SYMBOL(down_write_killable_nested);
195
196void up_read_non_owner(struct rw_semaphore *sem)
197{
198	__up_read(sem);
199}
200
201EXPORT_SYMBOL(up_read_non_owner);
202
203#endif
204
205