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_preempt_disable(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 one the synchronize_sched() 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        barrier();
  51        /*
  52         * The barrier() prevents the compiler from
  53         * bleeding the critical section out.
  54         */
  55}
  56
  57static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
  58{
  59        percpu_down_read_preempt_disable(sem);
  60        preempt_enable();
  61}
  62
  63static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
  64{
  65        int ret = 1;
  66
  67        preempt_disable();
  68        /*
  69         * Same as in percpu_down_read().
  70         */
  71        __this_cpu_inc(*sem->read_count);
  72        if (unlikely(!rcu_sync_is_idle(&sem->rss)))
  73                ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
  74        preempt_enable();
  75        /*
  76         * The barrier() from preempt_enable() prevents the compiler from
  77         * bleeding the critical section out.
  78         */
  79
  80        if (ret)
  81                rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
  82
  83        return ret;
  84}
  85
  86static inline void percpu_up_read_preempt_enable(struct percpu_rw_semaphore *sem)
  87{
  88        /*
  89         * The barrier() prevents the compiler from
  90         * bleeding the critical section out.
  91         */
  92        barrier();
  93        /*
  94         * Same as in percpu_down_read().
  95         */
  96        if (likely(rcu_sync_is_idle(&sem->rss)))
  97                __this_cpu_dec(*sem->read_count);
  98        else
  99                __percpu_up_read(sem); /* Unconditional memory barrier */
 100        preempt_enable();
 101
 102        rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
 103}
 104
 105static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
 106{
 107        preempt_disable();
 108        percpu_up_read_preempt_enable(sem);
 109}
 110
 111extern void percpu_down_write(struct percpu_rw_semaphore *);
 112extern void percpu_up_write(struct percpu_rw_semaphore *);
 113
 114extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
 115                                const char *, struct lock_class_key *);
 116
 117extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
 118
 119#define percpu_init_rwsem(sem)                                  \
 120({                                                              \
 121        static struct lock_class_key rwsem_key;                 \
 122        __percpu_init_rwsem(sem, #sem, &rwsem_key);             \
 123})
 124
 125#define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
 126
 127#define percpu_rwsem_assert_held(sem)                           \
 128        lockdep_assert_held(&(sem)->rw_sem)
 129
 130static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
 131                                        bool read, unsigned long ip)
 132{
 133        lock_release(&sem->rw_sem.dep_map, 1, ip);
 134#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 135        if (!read)
 136                sem->rw_sem.owner = RWSEM_OWNER_UNKNOWN;
 137#endif
 138}
 139
 140static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
 141                                        bool read, unsigned long ip)
 142{
 143        lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
 144#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
 145        if (!read)
 146                sem->rw_sem.owner = current;
 147#endif
 148}
 149
 150#endif
 151