summaryrefslogtreecommitdiff
path: root/include/linux/rwsem.h
blob: 6a6741440cb763a7272577f095542bd5a6067cb2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
/* rwsem.h: R/W semaphores, public interface
 *
 * Written by David Howells (dhowells@redhat.com).
 * Derived from asm-i386/semaphore.h
 */

#ifndef _LINUX_RWSEM_H
#define _LINUX_RWSEM_H

#include <linux/linkage.h>

#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/spinlock.h>

#include <asm/system.h>
#include <linux/atomic.h>

struct rw_semaphore;

#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
#include <linux/rwsem-spinlock.h> /* use a generic implementation */
#else
/* All arch specific implementations share the same struct */
struct rw_semaphore {
	long			count;
	spinlock_t		wait_lock;
	struct list_head	wait_list;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
	struct lockdep_map	dep_map;
#endif
};

extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);

/* Include the arch specific part */
#include <asm/rwsem.h>

/* In all implementations count != 0 means locked */
static inline int rwsem_is_locked(struct rw_semaphore *sem)
{
	return sem->count != 0;
}

#endif

/* Common initializer macros and functions */

#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
#else
# define __RWSEM_DEP_MAP_INIT(lockname)
#endif

#define __RWSEM_INITIALIZER(name) \
	{ RWSEM_UNLOCKED_VALUE, __SPIN_LOCK_UNLOCKED(name.wait_lock),	\
	  LIST_HEAD_INIT((name).wait_list) __RWSEM_DEP_MAP_INIT(name) }

#define DECLARE_RWSEM(name) \
	struct rw_semaphore name = __RWSEM_INITIALIZER(name)

extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
			 struct lock_class_key *key);

#define init_rwsem(sem)						\
do {								\
	static struct lock_class_key __key;			\
								\
	__init_rwsem((sem), #sem, &__key);			\
} while (0)

/*
 * lock for reading
 */
extern void down_read(struct rw_semaphore *sem);

/*
 * trylock for reading -- returns 1 if successful, 0 if contention
 */
extern int down_read_trylock(struct rw_semaphore *sem);

/*
 * lock for writing
 */
extern void down_write(struct rw_semaphore *sem);

/*
 * trylock for writing -- returns 1 if successful, 0 if contention
 */
extern int down_write_trylock(struct rw_semaphore *sem);

/*
 * release a read lock
 */
extern void up_read(struct rw_semaphore *sem);

/*
 * release a write lock
 */
extern void up_write(struct rw_semaphore *sem);

/*
 * downgrade write lock to read lock
 */
extern void downgrade_write(struct rw_semaphore *sem);

#ifdef CONFIG_DEBUG_LOCK_ALLOC
/*
 * nested locking. NOTE: rwsems are not allowed to recurse
 * (which occurs if the same task tries to acquire the same
 * lock instance multiple times), but multiple locks of the
 * same lock class might be taken, if the order of the locks
 * is always the same. This ordering rule can be expressed
 * to lockdep via the _nested() APIs, but enumerating the
 * subclasses that are used. (If the nesting relationship is
 * static then another method for expressing nested locking is
 * the explicit definition of lock class keys and the use of
 * lockdep_set_class() at lock initialization time.
 * See Documentation/lockdep-design.txt for more details.)
 */
extern void down_read_nested(struct rw_semaphore *sem, int subclass);
extern void down_write_nested(struct rw_semaphore *sem, int subclass);
#else
# define down_read_nested(sem, subclass)		down_read(sem)
# define down_write_nested(sem, subclass)	down_write(sem)
#endif

#endif /* _LINUX_RWSEM_H */