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 <asm/system.h>
14 #include <linux/atomic.h>
15
16 /*
17 * lock for reading
18 */
down_read(struct rw_semaphore * sem)19 void __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
27 EXPORT_SYMBOL(down_read);
28
29 /*
30 * trylock for reading -- returns 1 if successful, 0 if contention
31 */
down_read_trylock(struct rw_semaphore * sem)32 int 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
41 EXPORT_SYMBOL(down_read_trylock);
42
43 /*
44 * lock for writing
45 */
down_write(struct rw_semaphore * sem)46 void __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
54 EXPORT_SYMBOL(down_write);
55
56 /*
57 * trylock for writing -- returns 1 if successful, 0 if contention
58 */
down_write_trylock(struct rw_semaphore * sem)59 int 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
68 EXPORT_SYMBOL(down_write_trylock);
69
70 /*
71 * release a read lock
72 */
up_read(struct rw_semaphore * sem)73 void up_read(struct rw_semaphore *sem)
74 {
75 rwsem_release(&sem->dep_map, 1, _RET_IP_);
76
77 __up_read(sem);
78 }
79
80 EXPORT_SYMBOL(up_read);
81
82 /*
83 * release a write lock
84 */
up_write(struct rw_semaphore * sem)85 void up_write(struct rw_semaphore *sem)
86 {
87 rwsem_release(&sem->dep_map, 1, _RET_IP_);
88
89 __up_write(sem);
90 }
91
92 EXPORT_SYMBOL(up_write);
93
94 /*
95 * downgrade write lock to read lock
96 */
downgrade_write(struct rw_semaphore * sem)97 void 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
106 EXPORT_SYMBOL(downgrade_write);
107
108 #ifdef CONFIG_DEBUG_LOCK_ALLOC
109
down_read_nested(struct rw_semaphore * sem,int subclass)110 void 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
118 EXPORT_SYMBOL(down_read_nested);
119
down_write_nested(struct rw_semaphore * sem,int subclass)120 void 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
128 EXPORT_SYMBOL(down_write_nested);
129
130 #endif
131
132
133