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