Linux kernel mirror (for testing)
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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/rwsem.h>
7#include <linux/percpu.h>
8#include <linux/rcuwait.h>
9#include <linux/rcu_sync.h>
10#include <linux/lockdep.h>
11
12struct percpu_rw_semaphore {
13 struct rcu_sync rss;
14 unsigned int __percpu *read_count;
15 struct rw_semaphore rw_sem; /* slowpath */
16 struct rcuwait writer; /* blocked writer */
17 int readers_block;
18};
19
20#define __DEFINE_PERCPU_RWSEM(name, is_static) \
21static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name); \
22is_static struct percpu_rw_semaphore name = { \
23 .rss = __RCU_SYNC_INITIALIZER(name.rss), \
24 .read_count = &__percpu_rwsem_rc_##name, \
25 .rw_sem = __RWSEM_INITIALIZER(name.rw_sem), \
26 .writer = __RCUWAIT_INITIALIZER(name.writer), \
27}
28#define DEFINE_PERCPU_RWSEM(name) \
29 __DEFINE_PERCPU_RWSEM(name, /* not static */)
30#define DEFINE_STATIC_PERCPU_RWSEM(name) \
31 __DEFINE_PERCPU_RWSEM(name, static)
32
33extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
34extern void __percpu_up_read(struct percpu_rw_semaphore *);
35
36static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
37{
38 might_sleep();
39
40 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 0, _RET_IP_);
41
42 preempt_disable();
43 /*
44 * We are in an RCU-sched read-side critical section, so the writer
45 * cannot both change sem->state from readers_fast and start checking
46 * counters while we are here. So if we see !sem->state, we know that
47 * the writer won't be checking until we're past the preempt_enable()
48 * and that once the synchronize_rcu() is done, the writer will see
49 * anything we did within this RCU-sched read-size critical section.
50 */
51 __this_cpu_inc(*sem->read_count);
52 if (unlikely(!rcu_sync_is_idle(&sem->rss)))
53 __percpu_down_read(sem, false); /* Unconditional memory barrier */
54 /*
55 * The preempt_enable() prevents the compiler from
56 * bleeding the critical section out.
57 */
58 preempt_enable();
59}
60
61static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
62{
63 int ret = 1;
64
65 preempt_disable();
66 /*
67 * Same as in percpu_down_read().
68 */
69 __this_cpu_inc(*sem->read_count);
70 if (unlikely(!rcu_sync_is_idle(&sem->rss)))
71 ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
72 preempt_enable();
73 /*
74 * The barrier() from preempt_enable() prevents the compiler from
75 * bleeding the critical section out.
76 */
77
78 if (ret)
79 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
80
81 return ret;
82}
83
84static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
85{
86 preempt_disable();
87 /*
88 * Same as in percpu_down_read().
89 */
90 if (likely(rcu_sync_is_idle(&sem->rss)))
91 __this_cpu_dec(*sem->read_count);
92 else
93 __percpu_up_read(sem); /* Unconditional memory barrier */
94 preempt_enable();
95
96 rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
97}
98
99extern void percpu_down_write(struct percpu_rw_semaphore *);
100extern void percpu_up_write(struct percpu_rw_semaphore *);
101
102extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
103 const char *, struct lock_class_key *);
104
105extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
106
107#define percpu_init_rwsem(sem) \
108({ \
109 static struct lock_class_key rwsem_key; \
110 __percpu_init_rwsem(sem, #sem, &rwsem_key); \
111})
112
113#define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
114
115#define percpu_rwsem_assert_held(sem) \
116 lockdep_assert_held(&(sem)->rw_sem)
117
118static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
119 bool read, unsigned long ip)
120{
121 lock_release(&sem->rw_sem.dep_map, 1, ip);
122#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
123 if (!read)
124 atomic_long_set(&sem->rw_sem.owner, RWSEM_OWNER_UNKNOWN);
125#endif
126}
127
128static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
129 bool read, unsigned long ip)
130{
131 lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
132#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
133 if (!read)
134 atomic_long_set(&sem->rw_sem.owner, (long)current);
135#endif
136}
137
138#endif