LXR linux/include/linux/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/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
 139