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 */
down_read(struct rw_semaphore * sem)18 void __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
26 EXPORT_SYMBOL(down_read);
27
28 /*
29 * trylock for reading -- returns 1 if successful, 0 if contention
30 */
down_read_trylock(struct rw_semaphore * sem)31 int 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
40 EXPORT_SYMBOL(down_read_trylock);
41
42 /*
43 * lock for writing
44 */
down_write(struct rw_semaphore * sem)45 void __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
53 EXPORT_SYMBOL(down_write);
54
55 /*
56 * trylock for writing -- returns 1 if successful, 0 if contention
57 */
down_write_trylock(struct rw_semaphore * sem)58 int 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
67 EXPORT_SYMBOL(down_write_trylock);
68
69 /*
70 * release a read lock
71 */
up_read(struct rw_semaphore * sem)72 void up_read(struct rw_semaphore *sem)
73 {
74 rwsem_release(&sem->dep_map, 1, _RET_IP_);
75
76 __up_read(sem);
77 }
78
79 EXPORT_SYMBOL(up_read);
80
81 /*
82 * release a write lock
83 */
up_write(struct rw_semaphore * sem)84 void up_write(struct rw_semaphore *sem)
85 {
86 rwsem_release(&sem->dep_map, 1, _RET_IP_);
87
88 __up_write(sem);
89 }
90
91 EXPORT_SYMBOL(up_write);
92
93 /*
94 * downgrade write lock to read lock
95 */
downgrade_write(struct rw_semaphore * sem)96 void 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
105 EXPORT_SYMBOL(downgrade_write);
106
107 #ifdef CONFIG_DEBUG_LOCK_ALLOC
108
down_read_nested(struct rw_semaphore * sem,int subclass)109 void 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
117 EXPORT_SYMBOL(down_read_nested);
118
down_write_nested(struct rw_semaphore * sem,int subclass)119 void 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
127 EXPORT_SYMBOL(down_write_nested);
128
129 #endif
130
131
132