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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#include <linux/atomic.h>
17#include <linux/err.h>
18#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
19#include <linux/osq_lock.h>
20#endif
21
22struct rw_semaphore;
23
24#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
25#include <linux/rwsem-spinlock.h> /* use a generic implementation */
26#else
27/* All arch specific implementations share the same struct */
28struct rw_semaphore {
29 long count;
30 struct list_head wait_list;
31 raw_spinlock_t wait_lock;
32#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
33 struct optimistic_spin_queue osq; /* spinner MCS lock */
34 /*
35 * Write owner. Used as a speculative check to see
36 * if the owner is running on the cpu.
37 */
38 struct task_struct *owner;
39#endif
40#ifdef CONFIG_DEBUG_LOCK_ALLOC
41 struct lockdep_map dep_map;
42#endif
43};
44
45extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
46extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
47extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
48extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
49extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
50
51/* Include the arch specific part */
52#include <asm/rwsem.h>
53
54/* In all implementations count != 0 means locked */
55static inline int rwsem_is_locked(struct rw_semaphore *sem)
56{
57 return sem->count != 0;
58}
59
60#endif
61
62/* Common initializer macros and functions */
63
64#ifdef CONFIG_DEBUG_LOCK_ALLOC
65# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
66#else
67# define __RWSEM_DEP_MAP_INIT(lockname)
68#endif
69
70#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
71#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
72#else
73#define __RWSEM_OPT_INIT(lockname)
74#endif
75
76#define __RWSEM_INITIALIZER(name) \
77 { .count = RWSEM_UNLOCKED_VALUE, \
78 .wait_list = LIST_HEAD_INIT((name).wait_list), \
79 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
80 __RWSEM_OPT_INIT(name) \
81 __RWSEM_DEP_MAP_INIT(name) }
82
83#define DECLARE_RWSEM(name) \
84 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
85
86extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
87 struct lock_class_key *key);
88
89#define init_rwsem(sem) \
90do { \
91 static struct lock_class_key __key; \
92 \
93 __init_rwsem((sem), #sem, &__key); \
94} while (0)
95
96/*
97 * This is the same regardless of which rwsem implementation that is being used.
98 * It is just a heuristic meant to be called by somebody alreadying holding the
99 * rwsem to see if somebody from an incompatible type is wanting access to the
100 * lock.
101 */
102static inline int rwsem_is_contended(struct rw_semaphore *sem)
103{
104 return !list_empty(&sem->wait_list);
105}
106
107/*
108 * lock for reading
109 */
110extern void down_read(struct rw_semaphore *sem);
111
112/*
113 * trylock for reading -- returns 1 if successful, 0 if contention
114 */
115extern int down_read_trylock(struct rw_semaphore *sem);
116
117/*
118 * lock for writing
119 */
120extern void down_write(struct rw_semaphore *sem);
121extern int __must_check down_write_killable(struct rw_semaphore *sem);
122
123/*
124 * trylock for writing -- returns 1 if successful, 0 if contention
125 */
126extern int down_write_trylock(struct rw_semaphore *sem);
127
128/*
129 * release a read lock
130 */
131extern void up_read(struct rw_semaphore *sem);
132
133/*
134 * release a write lock
135 */
136extern void up_write(struct rw_semaphore *sem);
137
138/*
139 * downgrade write lock to read lock
140 */
141extern void downgrade_write(struct rw_semaphore *sem);
142
143#ifdef CONFIG_DEBUG_LOCK_ALLOC
144/*
145 * nested locking. NOTE: rwsems are not allowed to recurse
146 * (which occurs if the same task tries to acquire the same
147 * lock instance multiple times), but multiple locks of the
148 * same lock class might be taken, if the order of the locks
149 * is always the same. This ordering rule can be expressed
150 * to lockdep via the _nested() APIs, but enumerating the
151 * subclasses that are used. (If the nesting relationship is
152 * static then another method for expressing nested locking is
153 * the explicit definition of lock class keys and the use of
154 * lockdep_set_class() at lock initialization time.
155 * See Documentation/locking/lockdep-design.txt for more details.)
156 */
157extern void down_read_nested(struct rw_semaphore *sem, int subclass);
158extern void down_write_nested(struct rw_semaphore *sem, int subclass);
159extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
160extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
161
162# define down_write_nest_lock(sem, nest_lock) \
163do { \
164 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
165 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
166} while (0);
167
168/*
169 * Take/release a lock when not the owner will release it.
170 *
171 * [ This API should be avoided as much as possible - the
172 * proper abstraction for this case is completions. ]
173 */
174extern void down_read_non_owner(struct rw_semaphore *sem);
175extern void up_read_non_owner(struct rw_semaphore *sem);
176#else
177# define down_read_nested(sem, subclass) down_read(sem)
178# define down_write_nest_lock(sem, nest_lock) down_write(sem)
179# define down_write_nested(sem, subclass) down_write(sem)
180# define down_write_killable_nested(sem, subclass) down_write_killable(sem)
181# define down_read_non_owner(sem) down_read(sem)
182# define up_read_non_owner(sem) up_read(sem)
183#endif
184
185#endif /* _LINUX_RWSEM_H */