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1/* SPDX-License-Identifier: GPL-2.0 */
2/* rwsem.h: R/W semaphores, public interface
3 *
4 * Written by David Howells (dhowells@redhat.com).
5 * Derived from asm-i386/semaphore.h
6 */
7
8#ifndef _LINUX_RWSEM_H
9#define _LINUX_RWSEM_H
10
11#include <linux/linkage.h>
12
13#include <linux/types.h>
14#include <linux/kernel.h>
15#include <linux/list.h>
16#include <linux/spinlock.h>
17#include <linux/atomic.h>
18#include <linux/err.h>
19#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
20#include <linux/osq_lock.h>
21#endif
22
23struct rw_semaphore;
24
25#ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
26#include <linux/rwsem-spinlock.h> /* use a generic implementation */
27#define __RWSEM_INIT_COUNT(name) .count = RWSEM_UNLOCKED_VALUE
28#else
29/* All arch specific implementations share the same struct */
30struct rw_semaphore {
31 atomic_long_t count;
32 struct list_head wait_list;
33 raw_spinlock_t wait_lock;
34#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
35 struct optimistic_spin_queue osq; /* spinner MCS lock */
36 /*
37 * Write owner. Used as a speculative check to see
38 * if the owner is running on the cpu.
39 */
40 struct task_struct *owner;
41#endif
42#ifdef CONFIG_DEBUG_LOCK_ALLOC
43 struct lockdep_map dep_map;
44#endif
45};
46
47extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
48extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem);
49extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
50extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
51extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
52extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
53
54/* Include the arch specific part */
55#include <asm/rwsem.h>
56
57/* In all implementations count != 0 means locked */
58static inline int rwsem_is_locked(struct rw_semaphore *sem)
59{
60 return atomic_long_read(&sem->count) != 0;
61}
62
63#define __RWSEM_INIT_COUNT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
64#endif
65
66/* Common initializer macros and functions */
67
68#ifdef CONFIG_DEBUG_LOCK_ALLOC
69# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
70#else
71# define __RWSEM_DEP_MAP_INIT(lockname)
72#endif
73
74#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
75#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
76#else
77#define __RWSEM_OPT_INIT(lockname)
78#endif
79
80#define __RWSEM_INITIALIZER(name) \
81 { __RWSEM_INIT_COUNT(name), \
82 .wait_list = LIST_HEAD_INIT((name).wait_list), \
83 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
84 __RWSEM_OPT_INIT(name) \
85 __RWSEM_DEP_MAP_INIT(name) }
86
87#define DECLARE_RWSEM(name) \
88 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
89
90extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
91 struct lock_class_key *key);
92
93#define init_rwsem(sem) \
94do { \
95 static struct lock_class_key __key; \
96 \
97 __init_rwsem((sem), #sem, &__key); \
98} while (0)
99
100/*
101 * This is the same regardless of which rwsem implementation that is being used.
102 * It is just a heuristic meant to be called by somebody alreadying holding the
103 * rwsem to see if somebody from an incompatible type is wanting access to the
104 * lock.
105 */
106static inline int rwsem_is_contended(struct rw_semaphore *sem)
107{
108 return !list_empty(&sem->wait_list);
109}
110
111/*
112 * lock for reading
113 */
114extern void down_read(struct rw_semaphore *sem);
115
116/*
117 * trylock for reading -- returns 1 if successful, 0 if contention
118 */
119extern int down_read_trylock(struct rw_semaphore *sem);
120
121/*
122 * lock for writing
123 */
124extern void down_write(struct rw_semaphore *sem);
125extern int __must_check down_write_killable(struct rw_semaphore *sem);
126
127/*
128 * trylock for writing -- returns 1 if successful, 0 if contention
129 */
130extern int down_write_trylock(struct rw_semaphore *sem);
131
132/*
133 * release a read lock
134 */
135extern void up_read(struct rw_semaphore *sem);
136
137/*
138 * release a write lock
139 */
140extern void up_write(struct rw_semaphore *sem);
141
142/*
143 * downgrade write lock to read lock
144 */
145extern void downgrade_write(struct rw_semaphore *sem);
146
147#ifdef CONFIG_DEBUG_LOCK_ALLOC
148/*
149 * nested locking. NOTE: rwsems are not allowed to recurse
150 * (which occurs if the same task tries to acquire the same
151 * lock instance multiple times), but multiple locks of the
152 * same lock class might be taken, if the order of the locks
153 * is always the same. This ordering rule can be expressed
154 * to lockdep via the _nested() APIs, but enumerating the
155 * subclasses that are used. (If the nesting relationship is
156 * static then another method for expressing nested locking is
157 * the explicit definition of lock class keys and the use of
158 * lockdep_set_class() at lock initialization time.
159 * See Documentation/locking/lockdep-design.txt for more details.)
160 */
161extern void down_read_nested(struct rw_semaphore *sem, int subclass);
162extern void down_write_nested(struct rw_semaphore *sem, int subclass);
163extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
164extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
165
166# define down_write_nest_lock(sem, nest_lock) \
167do { \
168 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
169 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
170} while (0);
171
172/*
173 * Take/release a lock when not the owner will release it.
174 *
175 * [ This API should be avoided as much as possible - the
176 * proper abstraction for this case is completions. ]
177 */
178extern void down_read_non_owner(struct rw_semaphore *sem);
179extern void up_read_non_owner(struct rw_semaphore *sem);
180#else
181# define down_read_nested(sem, subclass) down_read(sem)
182# define down_write_nest_lock(sem, nest_lock) down_write(sem)
183# define down_write_nested(sem, subclass) down_write(sem)
184# define down_write_killable_nested(sem, subclass) down_write_killable(sem)
185# define down_read_non_owner(sem) down_read(sem)
186# define up_read_non_owner(sem) up_read(sem)
187#endif
188
189#endif /* _LINUX_RWSEM_H */