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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _LINUX_PERCPU_RWSEM_H
3#define _LINUX_PERCPU_RWSEM_H
4
5#include <linux/atomic.h>
6#include <linux/percpu.h>
7#include <linux/rcuwait.h>
8#include <linux/wait.h>
9#include <linux/rcu_sync.h>
10#include <linux/lockdep.h>
11#include <linux/cleanup.h>
12
13struct percpu_rw_semaphore {
14 struct rcu_sync rss;
15 unsigned int __percpu *read_count;
16 struct rcuwait writer;
17 wait_queue_head_t waiters;
18 atomic_t block;
19#ifdef CONFIG_DEBUG_LOCK_ALLOC
20 struct lockdep_map dep_map;
21#endif
22};
23
24#ifdef CONFIG_DEBUG_LOCK_ALLOC
25#define __PERCPU_RWSEM_DEP_MAP_INIT(lockname) .dep_map = { .name = #lockname },
26#else
27#define __PERCPU_RWSEM_DEP_MAP_INIT(lockname)
28#endif
29
30#define __DEFINE_PERCPU_RWSEM(name, is_static) \
31static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name); \
32is_static struct percpu_rw_semaphore name = { \
33 .rss = __RCU_SYNC_INITIALIZER(name.rss), \
34 .read_count = &__percpu_rwsem_rc_##name, \
35 .writer = __RCUWAIT_INITIALIZER(name.writer), \
36 .waiters = __WAIT_QUEUE_HEAD_INITIALIZER(name.waiters), \
37 .block = ATOMIC_INIT(0), \
38 __PERCPU_RWSEM_DEP_MAP_INIT(name) \
39}
40
41#define DEFINE_PERCPU_RWSEM(name) \
42 __DEFINE_PERCPU_RWSEM(name, /* not static */)
43#define DEFINE_STATIC_PERCPU_RWSEM(name) \
44 __DEFINE_PERCPU_RWSEM(name, static)
45
46extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool, bool);
47
48static inline void percpu_down_read_internal(struct percpu_rw_semaphore *sem,
49 bool freezable)
50{
51 might_sleep();
52
53 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
54
55 preempt_disable();
56 /*
57 * We are in an RCU-sched read-side critical section, so the writer
58 * cannot both change sem->state from readers_fast and start checking
59 * counters while we are here. So if we see !sem->state, we know that
60 * the writer won't be checking until we're past the preempt_enable()
61 * and that once the synchronize_rcu() is done, the writer will see
62 * anything we did within this RCU-sched read-size critical section.
63 */
64 if (likely(rcu_sync_is_idle(&sem->rss)))
65 this_cpu_inc(*sem->read_count);
66 else
67 __percpu_down_read(sem, false, freezable); /* Unconditional memory barrier */
68 /*
69 * The preempt_enable() prevents the compiler from
70 * bleeding the critical section out.
71 */
72 preempt_enable();
73}
74
75static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
76{
77 percpu_down_read_internal(sem, freezable: false);
78}
79
80static inline void percpu_down_read_freezable(struct percpu_rw_semaphore *sem,
81 bool freeze)
82{
83 percpu_down_read_internal(sem, freezable: freeze);
84}
85
86static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
87{
88 bool ret = true;
89
90 preempt_disable();
91 /*
92 * Same as in percpu_down_read().
93 */
94 if (likely(rcu_sync_is_idle(&sem->rss)))
95 this_cpu_inc(*sem->read_count);
96 else
97 ret = __percpu_down_read(sem, true, false); /* Unconditional memory barrier */
98 preempt_enable();
99 /*
100 * The barrier() from preempt_enable() prevents the compiler from
101 * bleeding the critical section out.
102 */
103
104 if (ret)
105 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
106
107 return ret;
108}
109
110static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
111{
112 rwsem_release(&sem->dep_map, _RET_IP_);
113
114 preempt_disable();
115 /*
116 * Same as in percpu_down_read().
117 */
118 if (likely(rcu_sync_is_idle(&sem->rss))) {
119 this_cpu_dec(*sem->read_count);
120 } else {
121 /*
122 * slowpath; reader will only ever wake a single blocked
123 * writer.
124 */
125 smp_mb(); /* B matches C */
126 /*
127 * In other words, if they see our decrement (presumably to
128 * aggregate zero, as that is the only time it matters) they
129 * will also see our critical section.
130 */
131 this_cpu_dec(*sem->read_count);
132 rcuwait_wake_up(w: &sem->writer);
133 }
134 preempt_enable();
135}
136
137extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
138extern void percpu_down_write(struct percpu_rw_semaphore *);
139extern void percpu_up_write(struct percpu_rw_semaphore *);
140
141DEFINE_GUARD(percpu_read, struct percpu_rw_semaphore *,
142 percpu_down_read(_T), percpu_up_read(_T))
143DEFINE_GUARD_COND(percpu_read, _try, percpu_down_read_trylock(_T))
144
145DEFINE_GUARD(percpu_write, struct percpu_rw_semaphore *,
146 percpu_down_write(_T), percpu_up_write(_T))
147
148static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
149{
150 return atomic_read(v: &sem->block);
151}
152
153extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
154 const char *, struct lock_class_key *);
155
156extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
157
158#define percpu_init_rwsem(sem) \
159({ \
160 static struct lock_class_key rwsem_key; \
161 __percpu_init_rwsem(sem, #sem, &rwsem_key); \
162})
163
164#define percpu_rwsem_is_held(sem) lockdep_is_held(sem)
165#define percpu_rwsem_assert_held(sem) lockdep_assert_held(sem)
166
167static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
168 unsigned long ip)
169{
170 lock_release(lock: &sem->dep_map, ip);
171}
172
173static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
174 bool read, unsigned long ip)
175{
176 lock_acquire(lock: &sem->dep_map, subclass: 0, trylock: 1, read, check: 1, NULL, ip);
177}
178
179#endif
180

source code of linux/include/linux/percpu-rwsem.h