Quelle percpu-rwsem.h Sprache: C

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef _LINUX_PERCPU_RWSEM_H
#define _LINUX_PERCPU_RWSEM_H

#include <linux/atomic.h>
#include <linux/percpu.h>
#include <linux/rcuwait.h>
#include <linux/wait.h>
#include <linux/rcu_sync.h>
#include <linux/lockdep.h>
#include <linux/cleanup.h>

struct percpu_rw_semaphore {
struct rcu_sync  rss;
unsigned int __percpu *read_count;
struct rcuwait  writer;
wait_queue_head_t waiters;
atomic_t  block;
#ifdef CONFIG_DEBUG_LOCK_ALLOC
struct lockdep_map dep_map;
#endif
};

#ifdef CONFIG_DEBUG_LOCK_ALLOC
#define __PERCPU_RWSEM_DEP_MAP_INIT(lockname) .dep_map = { .name = #lockname },
#else
#define __PERCPU_RWSEM_DEP_MAP_INIT(lockname)
#endif

#define __DEFINE_PERCPU_RWSEM(name, is_static)    \
static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name);  \
is_static struct percpu_rw_semaphore name = {    \
.rss = __RCU_SYNC_INITIALIZER(name.rss),   \
.read_count = &__percpu_rwsem_rc_##name,   \
.writer = __RCUWAIT_INITIALIZER(name.writer),   \
.waiters = __WAIT_QUEUE_HEAD_INITIALIZER(name.waiters),  \
.block = ATOMIC_INIT(0),     \
__PERCPU_RWSEM_DEP_MAP_INIT(name)    \
}

#define DEFINE_PERCPU_RWSEM(name)  \
__DEFINE_PERCPU_RWSEM(name, /* not static */)
#define DEFINE_STATIC_PERCPU_RWSEM(name) \
__DEFINE_PERCPU_RWSEM(name, static)

extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool, bool);

static inline void percpu_down_read_internal(struct percpu_rw_semaphore *sem,
          bool freezable)
{
might_sleep();

rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);

preempt_disable();
/*
* We are in an RCU-sched read-side critical section, so the writer
* cannot both change sem->state from readers_fast and start checking
* counters while we are here. So if we see !sem->state, we know that
* the writer won't be checking until we're past the preempt_enable()
* and that once the synchronize_rcu() is done, the writer will see
* anything we did within this RCU-sched read-size critical section.
*/
if (likely(rcu_sync_is_idle(&sem->rss)))
  this_cpu_inc(*sem->read_count);
else
  __percpu_down_read(sem, false, freezable); /* Unconditional memory barrier */
/*
* The preempt_enable() prevents the compiler from
* bleeding the critical section out.
*/
preempt_enable();
}

static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
{
percpu_down_read_internal(sem, false);
}

static inline void percpu_down_read_freezable(struct percpu_rw_semaphore *sem,
           bool freeze)
{
percpu_down_read_internal(sem, freeze);
}

static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
{
bool ret = true;

preempt_disable();
/*
* Same as in percpu_down_read().
*/
if (likely(rcu_sync_is_idle(&sem->rss)))
  this_cpu_inc(*sem->read_count);
else
  ret = __percpu_down_read(sem, true, false); /* Unconditional memory barrier */
preempt_enable();
/*
* The barrier() from preempt_enable() prevents the compiler from
* bleeding the critical section out.
*/

if (ret)
  rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);

return ret;
}

static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
{
rwsem_release(&sem->dep_map, _RET_IP_);

preempt_disable();
/*
* Same as in percpu_down_read().
*/
if (likely(rcu_sync_is_idle(&sem->rss))) {
  this_cpu_dec(*sem->read_count);
} else {
  /*
* slowpath; reader will only ever wake a single blocked
* writer.
*/
  smp_mb(); /* B matches C */
  /*
* In other words, if they see our decrement (presumably to
* aggregate zero, as that is the only time it matters) they
* will also see our critical section.
*/
  this_cpu_dec(*sem->read_count);
  rcuwait_wake_up(&sem->writer);
}
preempt_enable();
}

extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
extern void percpu_down_write(struct percpu_rw_semaphore *);
extern void percpu_up_write(struct percpu_rw_semaphore *);

DEFINE_GUARD(percpu_read, struct percpu_rw_semaphore *,
      percpu_down_read(_T), percpu_up_read(_T))
DEFINE_GUARD_COND(percpu_read, _try, percpu_down_read_trylock(_T))

DEFINE_GUARD(percpu_write, struct percpu_rw_semaphore *,
      percpu_down_write(_T), percpu_up_write(_T))

static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
{
return atomic_read(&sem->block);
}

extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
    const char *, struct lock_class_key *);

extern void percpu_free_rwsem(struct percpu_rw_semaphore *);

#define percpu_init_rwsem(sem)     \
({        \
static struct lock_class_key rwsem_key;   \
__percpu_init_rwsem(sem, #sem, &rwsem_key);  \
})

#define percpu_rwsem_is_held(sem) lockdep_is_held(sem)
#define percpu_rwsem_assert_held(sem) lockdep_assert_held(sem)

static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
     unsigned long ip)
{
lock_release(&sem->dep_map, ip);
}

static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
     bool read, unsigned long ip)
{
lock_acquire(&sem->dep_map, 0, 1, read, 1, NULL, ip);
}

#endif

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