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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
47/*
48 * Setting bit 0 of the owner field with other non-zero bits will indicate
49 * that the rwsem is writer-owned with an unknown owner.
50 */
51#define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-1L)
52
53extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
54extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem);
55extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
56extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem);
57extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
58extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
59
60/* Include the arch specific part */
61#include <asm/rwsem.h>
62
63/* In all implementations count != 0 means locked */
64static inline int rwsem_is_locked(struct rw_semaphore *sem)
65{
66 return atomic_long_read(&sem->count) != 0;
67}
68
69#define __RWSEM_INIT_COUNT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE)
70#endif
71
72/* Common initializer macros and functions */
73
74#ifdef CONFIG_DEBUG_LOCK_ALLOC
75# define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
76#else
77# define __RWSEM_DEP_MAP_INIT(lockname)
78#endif
79
80#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
81#define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
82#else
83#define __RWSEM_OPT_INIT(lockname)
84#endif
85
86#define __RWSEM_INITIALIZER(name) \
87 { __RWSEM_INIT_COUNT(name), \
88 .wait_list = LIST_HEAD_INIT((name).wait_list), \
89 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
90 __RWSEM_OPT_INIT(name) \
91 __RWSEM_DEP_MAP_INIT(name) }
92
93#define DECLARE_RWSEM(name) \
94 struct rw_semaphore name = __RWSEM_INITIALIZER(name)
95
96extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
97 struct lock_class_key *key);
98
99#define init_rwsem(sem) \
100do { \
101 static struct lock_class_key __key; \
102 \
103 __init_rwsem((sem), #sem, &__key); \
104} while (0)
105
106/*
107 * This is the same regardless of which rwsem implementation that is being used.
108 * It is just a heuristic meant to be called by somebody alreadying holding the
109 * rwsem to see if somebody from an incompatible type is wanting access to the
110 * lock.
111 */
112static inline int rwsem_is_contended(struct rw_semaphore *sem)
113{
114 return !list_empty(&sem->wait_list);
115}
116
117/*
118 * lock for reading
119 */
120extern void down_read(struct rw_semaphore *sem);
121extern int __must_check down_read_killable(struct rw_semaphore *sem);
122
123/*
124 * trylock for reading -- returns 1 if successful, 0 if contention
125 */
126extern int down_read_trylock(struct rw_semaphore *sem);
127
128/*
129 * lock for writing
130 */
131extern void down_write(struct rw_semaphore *sem);
132extern int __must_check down_write_killable(struct rw_semaphore *sem);
133
134/*
135 * trylock for writing -- returns 1 if successful, 0 if contention
136 */
137extern int down_write_trylock(struct rw_semaphore *sem);
138
139/*
140 * release a read lock
141 */
142extern void up_read(struct rw_semaphore *sem);
143
144/*
145 * release a write lock
146 */
147extern void up_write(struct rw_semaphore *sem);
148
149/*
150 * downgrade write lock to read lock
151 */
152extern void downgrade_write(struct rw_semaphore *sem);
153
154#ifdef CONFIG_DEBUG_LOCK_ALLOC
155/*
156 * nested locking. NOTE: rwsems are not allowed to recurse
157 * (which occurs if the same task tries to acquire the same
158 * lock instance multiple times), but multiple locks of the
159 * same lock class might be taken, if the order of the locks
160 * is always the same. This ordering rule can be expressed
161 * to lockdep via the _nested() APIs, but enumerating the
162 * subclasses that are used. (If the nesting relationship is
163 * static then another method for expressing nested locking is
164 * the explicit definition of lock class keys and the use of
165 * lockdep_set_class() at lock initialization time.
166 * See Documentation/locking/lockdep-design.txt for more details.)
167 */
168extern void down_read_nested(struct rw_semaphore *sem, int subclass);
169extern void down_write_nested(struct rw_semaphore *sem, int subclass);
170extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass);
171extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
172
173# define down_write_nest_lock(sem, nest_lock) \
174do { \
175 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
176 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \
177} while (0);
178
179/*
180 * Take/release a lock when not the owner will release it.
181 *
182 * [ This API should be avoided as much as possible - the
183 * proper abstraction for this case is completions. ]
184 */
185extern void down_read_non_owner(struct rw_semaphore *sem);
186extern void up_read_non_owner(struct rw_semaphore *sem);
187#else
188# define down_read_nested(sem, subclass) down_read(sem)
189# define down_write_nest_lock(sem, nest_lock) down_write(sem)
190# define down_write_nested(sem, subclass) down_write(sem)
191# define down_write_killable_nested(sem, subclass) down_write_killable(sem)
192# define down_read_non_owner(sem) down_read(sem)
193# define up_read_non_owner(sem) up_read(sem)
194#endif
195
196#endif /* _LINUX_RWSEM_H */