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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 <linux/atomic.h>
18
19 struct rw_semaphore;
20
21 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
22 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
23 #else
24 /* All arch specific implementations share the same struct */
25 struct rw_semaphore {
26 long count;
27 raw_spinlock_t wait_lock;
28 struct list_head wait_list;
29 #ifdef CONFIG_DEBUG_LOCK_ALLOC
30 struct lockdep_map dep_map;
31 #endif
32 };
33
34 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
35 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
36 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
37 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
38
39 /* Include the arch specific part */
40 #include <asm/rwsem.h>
41
42 /* In all implementations count != 0 means locked */
43 static inline int rwsem_is_locked(struct rw_semaphore *sem)
44 {
45 return sem->count != 0;
46 }
47
48 #endif
49
50 /* Common initializer macros and functions */
51
52 #ifdef CONFIG_DEBUG_LOCK_ALLOC
53 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
54 #else
55 # define __RWSEM_DEP_MAP_INIT(lockname)
56 #endif
57
58 #define __RWSEM_INITIALIZER(name) \
59 { RWSEM_UNLOCKED_VALUE, \
60 __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
61 LIST_HEAD_INIT((name).wait_list) \
62 __RWSEM_DEP_MAP_INIT(name) }
63
64 #define DECLARE_RWSEM(name) \
65 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
66
67 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
68 struct lock_class_key *key);
69
70 #define init_rwsem(sem) \
71 do { \
72 static struct lock_class_key __key; \
73 \
74 __init_rwsem((sem), #sem, &__key); \
75 } while (0)
76
77 /*
78 * lock for reading
79 */
80 extern void down_read(struct rw_semaphore *sem);
81
82 /*
83 * trylock for reading -- returns 1 if successful, 0 if contention
84 */
85 extern int down_read_trylock(struct rw_semaphore *sem);
86
87 /*
88 * lock for writing
89 */
90 extern void down_write(struct rw_semaphore *sem);
91
92 /*
93 * trylock for writing -- returns 1 if successful, 0 if contention
94 */
95 extern int down_write_trylock(struct rw_semaphore *sem);
96
97 /*
98 * release a read lock
99 */
100 extern void up_read(struct rw_semaphore *sem);
101
102 /*
103 * release a write lock
104 */
105 extern void up_write(struct rw_semaphore *sem);
106
107 /*
108 * downgrade write lock to read lock
109 */
110 extern void downgrade_write(struct rw_semaphore *sem);
111
112 #ifdef CONFIG_DEBUG_LOCK_ALLOC
113 /*
114 * nested locking. NOTE: rwsems are not allowed to recurse
115 * (which occurs if the same task tries to acquire the same
116 * lock instance multiple times), but multiple locks of the
117 * same lock class might be taken, if the order of the locks
118 * is always the same. This ordering rule can be expressed
119 * to lockdep via the _nested() APIs, but enumerating the
120 * subclasses that are used. (If the nesting relationship is
121 * static then another method for expressing nested locking is
122 * the explicit definition of lock class keys and the use of
123 * lockdep_set_class() at lock initialization time.
124 * See Documentation/lockdep-design.txt for more details.)
125 */
126 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
127 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
128 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
129
130 # define down_write_nest_lock(sem, nest_lock) \
131 do { \
132 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
133 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
134 } while (0);
135
136 #else
137 # define down_read_nested(sem, subclass) down_read(sem)
138 # define down_write_nest_lock(sem, nest_lock) down_write(sem)
139 # define down_write_nested(sem, subclass) down_write(sem)
140 #endif
141
142 #endif /* _LINUX_RWSEM_H */