Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
tjh.dev
kernel
os
linux
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
19struct optimistic_spin_queue;
20struct 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 */
26struct rw_semaphore {
27 long count;
28 raw_spinlock_t wait_lock;
29 struct list_head wait_list;
30#ifdef CONFIG_SMP
31 /*
32 * Write owner. Used as a speculative check to see
33 * if the owner is running on the cpu.
34 */
35 struct task_struct *owner;
36 struct optimistic_spin_queue *osq; /* spinner MCS lock */
37#endif
38#ifdef CONFIG_DEBUG_LOCK_ALLOC
39 struct lockdep_map dep_map;
40#endif
41};
42
43extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
44extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
45extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
46extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
47
48/* Include the arch specific part */
49#include <asm/rwsem.h>
50
51/* In all implementations count != 0 means locked */
52static inline int rwsem_is_locked(struct rw_semaphore *sem)
53{
54 return sem->count != 0;
55}
56
57#endif
58
59/* Common initializer macros and functions */
60
61#ifdef CONFIG_DEBUG_LOCK_ALLOC
62# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
63#else
64# define __RWSEM_DEP_MAP_INIT(lockname)
65#endif
66
67#if defined(CONFIG_SMP) && !defined(CONFIG_RWSEM_GENERIC_SPINLOCK)
68#define __RWSEM_INITIALIZER(name) \
69 { RWSEM_UNLOCKED_VALUE, \
70 __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
71 LIST_HEAD_INIT((name).wait_list), \
72 NULL, /* owner */ \
73 NULL /* mcs lock */ \
74 __RWSEM_DEP_MAP_INIT(name) }
75#else
76#define __RWSEM_INITIALIZER(name) \
77 { RWSEM_UNLOCKED_VALUE, \
78 __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock), \
79 LIST_HEAD_INIT((name).wait_list) \
80 __RWSEM_DEP_MAP_INIT(name) }
81#endif
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);
121
122/*
123 * trylock for writing -- returns 1 if successful, 0 if contention
124 */
125extern int down_write_trylock(struct rw_semaphore *sem);
126
127/*
128 * release a read lock
129 */
130extern void up_read(struct rw_semaphore *sem);
131
132/*
133 * release a write lock
134 */
135extern void up_write(struct rw_semaphore *sem);
136
137/*
138 * downgrade write lock to read lock
139 */
140extern void downgrade_write(struct rw_semaphore *sem);
141
142#ifdef CONFIG_DEBUG_LOCK_ALLOC
143/*
144 * nested locking. NOTE: rwsems are not allowed to recurse
145 * (which occurs if the same task tries to acquire the same
146 * lock instance multiple times), but multiple locks of the
147 * same lock class might be taken, if the order of the locks
148 * is always the same. This ordering rule can be expressed
149 * to lockdep via the _nested() APIs, but enumerating the
150 * subclasses that are used. (If the nesting relationship is
151 * static then another method for expressing nested locking is
152 * the explicit definition of lock class keys and the use of
153 * lockdep_set_class() at lock initialization time.
154 * See Documentation/lockdep-design.txt for more details.)
155 */
156extern void down_read_nested(struct rw_semaphore *sem, int subclass);
157extern void down_write_nested(struct rw_semaphore *sem, int subclass);
158extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
159
160# define down_write_nest_lock(sem, nest_lock) \
161do { \
162 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
163 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
164} while (0);
165
166/*
167 * Take/release a lock when not the owner will release it.
168 *
169 * [ This API should be avoided as much as possible - the
170 * proper abstraction for this case is completions. ]
171 */
172extern void down_read_non_owner(struct rw_semaphore *sem);
173extern void up_read_non_owner(struct rw_semaphore *sem);
174#else
175# define down_read_nested(sem, subclass) down_read(sem)
176# define down_write_nest_lock(sem, nest_lock) down_write(sem)
177# define down_write_nested(sem, subclass) down_write(sem)
178# define down_read_non_owner(sem) down_read(sem)
179# define up_read_non_owner(sem) up_read(sem)
180#endif
181
182#endif /* _LINUX_RWSEM_H */