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 */
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 rwsem_set_owner(sem);
53 }
54
55 EXPORT_SYMBOL(down_write);
56
57 /*
58 * trylock for writing -- returns 1 if successful, 0 if contention
59 */
down_write_trylock(struct rw_semaphore * sem)60 int 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
72 EXPORT_SYMBOL(down_write_trylock);
73
74 /*
75 * release a read lock
76 */
up_read(struct rw_semaphore * sem)77 void up_read(struct rw_semaphore *sem)
78 {
79 rwsem_release(&sem->dep_map, 1, _RET_IP_);
80
81 __up_read(sem);
82 }
83
84 EXPORT_SYMBOL(up_read);
85
86 /*
87 * release a write lock
88 */
up_write(struct rw_semaphore * sem)89 void 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
97 EXPORT_SYMBOL(up_write);
98
99 /*
100 * downgrade write lock to read lock
101 */
downgrade_write(struct rw_semaphore * sem)102 void 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
112 EXPORT_SYMBOL(downgrade_write);
113
114 #ifdef CONFIG_DEBUG_LOCK_ALLOC
115
down_read_nested(struct rw_semaphore * sem,int subclass)116 void 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
124 EXPORT_SYMBOL(down_read_nested);
125
_down_write_nest_lock(struct rw_semaphore * sem,struct lockdep_map * nest)126 void _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
135 EXPORT_SYMBOL(_down_write_nest_lock);
136
down_read_non_owner(struct rw_semaphore * sem)137 void down_read_non_owner(struct rw_semaphore *sem)
138 {
139 might_sleep();
140
141 __down_read(sem);
142 }
143
144 EXPORT_SYMBOL(down_read_non_owner);
145
down_write_nested(struct rw_semaphore * sem,int subclass)146 void 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
155 EXPORT_SYMBOL(down_write_nested);
156
up_read_non_owner(struct rw_semaphore * sem)157 void up_read_non_owner(struct rw_semaphore *sem)
158 {
159 __up_read(sem);
160 }
161
162 EXPORT_SYMBOL(up_read_non_owner);
163
164 #endif
165
166
167