percpu-rwsem.h

  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, 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, 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(&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(&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(&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(&sem->dep_map, 0, 1, read, 1, NULL, ip);
177}
178
179#endif