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git.proxmox.com Git - mirror_ubuntu-artful-kernel.git/blob - include/linux/rwsem.h
1 /* rwsem.h: R/W semaphores, public interface
3 * Written by David Howells (dhowells@redhat.com).
4 * Derived from asm-i386/semaphore.h
10 #include <linux/linkage.h>
12 #include <linux/types.h>
13 #include <linux/kernel.h>
14 #include <linux/list.h>
15 #include <linux/spinlock.h>
17 #include <linux/atomic.h>
21 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
22 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
24 /* All arch specific implementations share the same struct */
27 raw_spinlock_t wait_lock
;
28 struct list_head wait_list
;
29 #ifdef CONFIG_DEBUG_LOCK_ALLOC
30 struct lockdep_map dep_map
;
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
);
39 /* Include the arch specific part */
40 #include <asm/rwsem.h>
42 /* In all implementations count != 0 means locked */
43 static inline int rwsem_is_locked(struct rw_semaphore
*sem
)
45 return sem
->count
!= 0;
50 /* Common initializer macros and functions */
52 #ifdef CONFIG_DEBUG_LOCK_ALLOC
53 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
55 # define __RWSEM_DEP_MAP_INIT(lockname)
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) }
64 #define DECLARE_RWSEM(name) \
65 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
67 extern void __init_rwsem(struct rw_semaphore
*sem
, const char *name
,
68 struct lock_class_key
*key
);
70 #define init_rwsem(sem) \
72 static struct lock_class_key __key; \
74 __init_rwsem((sem), #sem, &__key); \
80 extern void down_read(struct rw_semaphore
*sem
);
83 * trylock for reading -- returns 1 if successful, 0 if contention
85 extern int down_read_trylock(struct rw_semaphore
*sem
);
90 extern void down_write(struct rw_semaphore
*sem
);
93 * trylock for writing -- returns 1 if successful, 0 if contention
95 extern int down_write_trylock(struct rw_semaphore
*sem
);
100 extern void up_read(struct rw_semaphore
*sem
);
103 * release a write lock
105 extern void up_write(struct rw_semaphore
*sem
);
108 * downgrade write lock to read lock
110 extern void downgrade_write(struct rw_semaphore
*sem
);
112 #ifdef CONFIG_DEBUG_LOCK_ALLOC
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.)
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
);
130 # define down_write_nest_lock(sem, nest_lock) \
132 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
133 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
137 * Take/release a lock when not the owner will release it.
139 * [ This API should be avoided as much as possible - the
140 * proper abstraction for this case is completions. ]
142 extern void down_read_non_owner(struct rw_semaphore
*sem
);
143 extern void up_read_non_owner(struct rw_semaphore
*sem
);
145 # define down_read_nested(sem, subclass) down_read(sem)
146 # define down_write_nest_lock(sem, nest_lock) down_write(sem)
147 # define down_write_nested(sem, subclass) down_write(sem)
148 # define down_read_non_owner(sem) down_read(sem)
149 # define up_read_non_owner(sem) up_read(sem)
152 #endif /* _LINUX_RWSEM_H */