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