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 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
rwsem_set_owner(struct rw_semaphore * sem)16 static inline void rwsem_set_owner(struct rw_semaphore *sem)
17 {
18 sem->owner = current;
19 }
20
rwsem_clear_owner(struct rw_semaphore * sem)21 static inline void rwsem_clear_owner(struct rw_semaphore *sem)
22 {
23 sem->owner = NULL;
24 }
25
26 #else
rwsem_set_owner(struct rw_semaphore * sem)27 static inline void rwsem_set_owner(struct rw_semaphore *sem)
28 {
29 }
30
rwsem_clear_owner(struct rw_semaphore * sem)31 static inline void rwsem_clear_owner(struct rw_semaphore *sem)
32 {
33 }
34 #endif
35
36 /*
37 * lock for reading
38 */
down_read(struct rw_semaphore * sem)39 void __sched down_read(struct rw_semaphore *sem)
40 {
41 might_sleep();
42 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
43
44 LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
45 }
46
47 EXPORT_SYMBOL(down_read);
48
49 /*
50 * trylock for reading -- returns 1 if successful, 0 if contention
51 */
down_read_trylock(struct rw_semaphore * sem)52 int down_read_trylock(struct rw_semaphore *sem)
53 {
54 int ret = __down_read_trylock(sem);
55
56 if (ret == 1)
57 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
58 return ret;
59 }
60
61 EXPORT_SYMBOL(down_read_trylock);
62
63 /*
64 * lock for writing
65 */
down_write(struct rw_semaphore * sem)66 void __sched down_write(struct rw_semaphore *sem)
67 {
68 might_sleep();
69 rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
70
71 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
72 rwsem_set_owner(sem);
73 }
74
75 EXPORT_SYMBOL(down_write);
76
77 /*
78 * trylock for writing -- returns 1 if successful, 0 if contention
79 */
down_write_trylock(struct rw_semaphore * sem)80 int down_write_trylock(struct rw_semaphore *sem)
81 {
82 int ret = __down_write_trylock(sem);
83
84 if (ret == 1) {
85 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
86 rwsem_set_owner(sem);
87 }
88
89 return ret;
90 }
91
92 EXPORT_SYMBOL(down_write_trylock);
93
94 /*
95 * release a read lock
96 */
up_read(struct rw_semaphore * sem)97 void up_read(struct rw_semaphore *sem)
98 {
99 rwsem_release(&sem->dep_map, 1, _RET_IP_);
100
101 __up_read(sem);
102 }
103
104 EXPORT_SYMBOL(up_read);
105
106 /*
107 * release a write lock
108 */
up_write(struct rw_semaphore * sem)109 void up_write(struct rw_semaphore *sem)
110 {
111 rwsem_release(&sem->dep_map, 1, _RET_IP_);
112
113 rwsem_clear_owner(sem);
114 __up_write(sem);
115 }
116
117 EXPORT_SYMBOL(up_write);
118
119 /*
120 * downgrade write lock to read lock
121 */
downgrade_write(struct rw_semaphore * sem)122 void downgrade_write(struct rw_semaphore *sem)
123 {
124 /*
125 * lockdep: a downgraded write will live on as a write
126 * dependency.
127 */
128 rwsem_clear_owner(sem);
129 __downgrade_write(sem);
130 }
131
132 EXPORT_SYMBOL(downgrade_write);
133
134 #ifdef CONFIG_DEBUG_LOCK_ALLOC
135
down_read_nested(struct rw_semaphore * sem,int subclass)136 void down_read_nested(struct rw_semaphore *sem, int subclass)
137 {
138 might_sleep();
139 rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
140
141 LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
142 }
143
144 EXPORT_SYMBOL(down_read_nested);
145
_down_write_nest_lock(struct rw_semaphore * sem,struct lockdep_map * nest)146 void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
147 {
148 might_sleep();
149 rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
150
151 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
152 rwsem_set_owner(sem);
153 }
154
155 EXPORT_SYMBOL(_down_write_nest_lock);
156
down_read_non_owner(struct rw_semaphore * sem)157 void down_read_non_owner(struct rw_semaphore *sem)
158 {
159 might_sleep();
160
161 __down_read(sem);
162 }
163
164 EXPORT_SYMBOL(down_read_non_owner);
165
down_write_nested(struct rw_semaphore * sem,int subclass)166 void down_write_nested(struct rw_semaphore *sem, int subclass)
167 {
168 might_sleep();
169 rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
170
171 LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
172 rwsem_set_owner(sem);
173 }
174
175 EXPORT_SYMBOL(down_write_nested);
176
up_read_non_owner(struct rw_semaphore * sem)177 void up_read_non_owner(struct rw_semaphore *sem)
178 {
179 __up_read(sem);
180 }
181
182 EXPORT_SYMBOL(up_read_non_owner);
183
184 #endif
185
186
187