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/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 void percpu_down_write(struct percpu_rw_semaphore *);
 125extern void percpu_up_write(struct percpu_rw_semaphore *);
 126
 127extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
 128                                const char *, struct lock_class_key *);
 129
 130extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
 131
 132#define percpu_init_rwsem(sem)                                  \
 133({                                                              \
 134        static struct lock_class_key rwsem_key;                 \
 135        __percpu_init_rwsem(sem, #sem, &rwsem_key);             \
 136})
 137
 138#define percpu_rwsem_is_held(sem)       lockdep_is_held(sem)
 139#define percpu_rwsem_assert_held(sem)   lockdep_assert_held(sem)
 140
 141static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
 142                                        bool read, unsigned long ip)
 143{
 144        lock_release(&sem->dep_map, ip);
 145}
 146
 147static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
 148                                        bool read, unsigned long ip)
 149{
 150        lock_acquire(&sem->dep_map, 0, 1, read, 1, NULL, ip);
 151}
 152
 153#endif
 154