1 /* rwsem.h: R/W semaphores, public interface
2 *
3 * Written by David Howells (dhowells@redhat.com).
4 * Derived from asm-i386/semaphore.h
5 */
6
7 #ifndef _LINUX_RWSEM_H
8 #define _LINUX_RWSEM_H
9
10 #include <linux/linkage.h>
11
12 #include <linux/types.h>
13 #include <linux/kernel.h>
14 #include <linux/list.h>
15 #include <linux/spinlock.h>
16
17 #include <asm/system.h>
18 #include <linux/atomic.h>
19
20 struct rw_semaphore;
21
22 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
23 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
24 #else
25 /* All arch specific implementations share the same struct */
26 struct rw_semaphore {
27 long count;
28 raw_spinlock_t wait_lock;
29 struct list_head wait_list;
30 #ifdef CONFIG_DEBUG_LOCK_ALLOC
31 struct lockdep_map dep_map;
32 #endif
33 };
34
35 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
36 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
37 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
38 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
39
40 /* Include the arch specific part */
41 #include <asm/rwsem.h>
42
43 /* In all implementations count != 0 means locked */
rwsem_is_locked(struct rw_semaphore * sem)44 static inline int rwsem_is_locked(struct rw_semaphore *sem)
45 {
46 return sem->count != 0;
47 }
48
49 #endif
50
51 /* Common initializer macros and functions */
52
53 #ifdef CONFIG_DEBUG_LOCK_ALLOC
54 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
55 #else
56 # define __RWSEM_DEP_MAP_INIT(lockname)
57 #endif
58
59 #define __RWSEM_INITIALIZER(name) \
60 { RWSEM_UNLOCKED_VALUE, \
61 __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
62 LIST_HEAD_INIT((name).wait_list) \
63 __RWSEM_DEP_MAP_INIT(name) }
64
65 #define DECLARE_RWSEM(name) \
66 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
67
68 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
69 struct lock_class_key *key);
70
71 #define init_rwsem(sem) \
72 do { \
73 static struct lock_class_key __key; \
74 \
75 __init_rwsem((sem), #sem, &__key); \
76 } while (0)
77
78 /*
79 * lock for reading
80 */
81 extern void down_read(struct rw_semaphore *sem);
82
83 /*
84 * trylock for reading -- returns 1 if successful, 0 if contention
85 */
86 extern int down_read_trylock(struct rw_semaphore *sem);
87
88 /*
89 * lock for writing
90 */
91 extern void down_write(struct rw_semaphore *sem);
92
93 /*
94 * trylock for writing -- returns 1 if successful, 0 if contention
95 */
96 extern int down_write_trylock(struct rw_semaphore *sem);
97
98 /*
99 * release a read lock
100 */
101 extern void up_read(struct rw_semaphore *sem);
102
103 /*
104 * release a write lock
105 */
106 extern void up_write(struct rw_semaphore *sem);
107
108 /*
109 * downgrade write lock to read lock
110 */
111 extern void downgrade_write(struct rw_semaphore *sem);
112
113 #ifdef CONFIG_DEBUG_LOCK_ALLOC
114 /*
115 * nested locking. NOTE: rwsems are not allowed to recurse
116 * (which occurs if the same task tries to acquire the same
117 * lock instance multiple times), but multiple locks of the
118 * same lock class might be taken, if the order of the locks
119 * is always the same. This ordering rule can be expressed
120 * to lockdep via the _nested() APIs, but enumerating the
121 * subclasses that are used. (If the nesting relationship is
122 * static then another method for expressing nested locking is
123 * the explicit definition of lock class keys and the use of
124 * lockdep_set_class() at lock initialization time.
125 * See Documentation/lockdep-design.txt for more details.)
126 */
127 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
128 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
129 #else
130 # define down_read_nested(sem, subclass) down_read(sem)
131 # define down_write_nested(sem, subclass) down_write(sem)
132 #endif
133
134 #endif /* _LINUX_RWSEM_H */
135