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
22 struct rw_semaphore;
23
24 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
25 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
26 #define __RWSEM_INIT_COUNT(name) .count = RWSEM_UNLOCKED_VALUE
27 #else
28 /* All arch specific implementations share the same struct */
29 struct rw_semaphore {
30 atomic_long_t count;
31 struct list_head wait_list;
32 raw_spinlock_t wait_lock;
33 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
34 struct optimistic_spin_queue osq; /* spinner MCS lock */
35 /*
36 * Write owner. Used as a speculative check to see
37 * if the owner is running on the cpu.
38 */
39 struct task_struct *owner;
40 #endif
41 #ifdef CONFIG_DEBUG_LOCK_ALLOC
42 struct lockdep_map dep_map;
43 #endif
44 };
45
46 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
47 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
48 extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
49 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
50 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
51
52 /* Include the arch specific part */
53 #include <asm/rwsem.h>
54
55 /* In all implementations count != 0 means locked */
rwsem_is_locked(struct rw_semaphore * sem)56 static inline int rwsem_is_locked(struct rw_semaphore *sem)
57 {
58 return atomic_long_read(&sem->count) != 0;
59 }
60
61 #define __RWSEM_INIT_COUNT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
62 #endif
63
64 /* Common initializer macros and functions */
65
66 #ifdef CONFIG_DEBUG_LOCK_ALLOC
67 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
68 #else
69 # define __RWSEM_DEP_MAP_INIT(lockname)
70 #endif
71
72 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
73 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
74 #else
75 #define __RWSEM_OPT_INIT(lockname)
76 #endif
77
78 #define __RWSEM_INITIALIZER(name) \
79 { __RWSEM_INIT_COUNT(name), \
80 .wait_list = LIST_HEAD_INIT((name).wait_list), \
81 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
82 __RWSEM_OPT_INIT(name) \
83 __RWSEM_DEP_MAP_INIT(name) }
84
85 #define DECLARE_RWSEM(name) \
86 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
87
88 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
89 struct lock_class_key *key);
90
91 #define init_rwsem(sem) \
92 do { \
93 static struct lock_class_key __key; \
94 \
95 __init_rwsem((sem), #sem, &__key); \
96 } while (0)
97
98 /*
99 * This is the same regardless of which rwsem implementation that is being used.
100 * It is just a heuristic meant to be called by somebody alreadying holding the
101 * rwsem to see if somebody from an incompatible type is wanting access to the
102 * lock.
103 */
rwsem_is_contended(struct rw_semaphore * sem)104 static inline int rwsem_is_contended(struct rw_semaphore *sem)
105 {
106 return !list_empty(&sem->wait_list);
107 }
108
109 /*
110 * lock for reading
111 */
112 extern void down_read(struct rw_semaphore *sem);
113
114 /*
115 * trylock for reading -- returns 1 if successful, 0 if contention
116 */
117 extern int down_read_trylock(struct rw_semaphore *sem);
118
119 /*
120 * lock for writing
121 */
122 extern void down_write(struct rw_semaphore *sem);
123 extern int __must_check down_write_killable(struct rw_semaphore *sem);
124
125 /*
126 * trylock for writing -- returns 1 if successful, 0 if contention
127 */
128 extern int down_write_trylock(struct rw_semaphore *sem);
129
130 /*
131 * release a read lock
132 */
133 extern void up_read(struct rw_semaphore *sem);
134
135 /*
136 * release a write lock
137 */
138 extern void up_write(struct rw_semaphore *sem);
139
140 /*
141 * downgrade write lock to read lock
142 */
143 extern void downgrade_write(struct rw_semaphore *sem);
144
145 #ifdef CONFIG_DEBUG_LOCK_ALLOC
146 /*
147 * nested locking. NOTE: rwsems are not allowed to recurse
148 * (which occurs if the same task tries to acquire the same
149 * lock instance multiple times), but multiple locks of the
150 * same lock class might be taken, if the order of the locks
151 * is always the same. This ordering rule can be expressed
152 * to lockdep via the _nested() APIs, but enumerating the
153 * subclasses that are used. (If the nesting relationship is
154 * static then another method for expressing nested locking is
155 * the explicit definition of lock class keys and the use of
156 * lockdep_set_class() at lock initialization time.
157 * See Documentation/locking/lockdep-design.txt for more details.)
158 */
159 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
160 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
161 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
162 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
163
164 # define down_write_nest_lock(sem, nest_lock) \
165 do { \
166 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
167 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
168 } while (0);
169
170 /*
171 * Take/release a lock when not the owner will release it.
172 *
173 * [ This API should be avoided as much as possible - the
174 * proper abstraction for this case is completions. ]
175 */
176 extern void down_read_non_owner(struct rw_semaphore *sem);
177 extern void up_read_non_owner(struct rw_semaphore *sem);
178 #else
179 # define down_read_nested(sem, subclass) down_read(sem)
180 # define down_write_nest_lock(sem, nest_lock) down_write(sem)
181 # define down_write_nested(sem, subclass) down_write(sem)
182 # define down_write_killable_nested(sem, subclass) down_write_killable(sem)
183 # define down_read_non_owner(sem) down_read(sem)
184 # define up_read_non_owner(sem) up_read(sem)
185 #endif
186
187 #endif /* _LINUX_RWSEM_H */
188