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_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