Root/kernel/rwsem.c

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
132

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