#ifndef _LINUX_PERCPU_RWSEM_H
  #define _LINUX_PERCPU_RWSEM_H

  #include <linux/atomic.h>

  #include <linux/rwsem.h>

  #include <linux/percpu.h>

  #include <linux/wait.h>

  #include <linux/rcu_sync.h>

  #include <linux/lockdep.h>

  
  struct percpu_rw_semaphore {

  	struct rcu_sync		rss;

  	unsigned int __percpu	*read_count;

  	struct rw_semaphore	rw_sem;

  	wait_queue_head_t	writer;
  	int			readers_block;

  };

  #define DEFINE_STATIC_PERCPU_RWSEM(name)				\
  static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name);		\
  static struct percpu_rw_semaphore name = {				\
  	.rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC),	\
  	.read_count = &__percpu_rwsem_rc_##name,			\
  	.rw_sem = __RWSEM_INITIALIZER(name.rw_sem),			\
  	.writer = __WAIT_QUEUE_HEAD_INITIALIZER(name.writer),		\
  }

  extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
  extern void __percpu_up_read(struct percpu_rw_semaphore *);

  static inline void percpu_down_read_preempt_disable(struct percpu_rw_semaphore *sem)

  {
  	might_sleep();
  
  	rwsem_acquire_read(&sem->rw_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 one the synchronize_sched() is done, the writer will see
  	 * anything we did within this RCU-sched read-size critical section.
  	 */
  	__this_cpu_inc(*sem->read_count);
  	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
  		__percpu_down_read(sem, false); /* Unconditional memory barrier */

  	barrier();

  	/*

  	 * The barrier() prevents the compiler from

  	 * bleeding the critical section out.
  	 */
  }

  static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
  {
  	percpu_down_read_preempt_disable(sem);
  	preempt_enable();
  }

  static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
  {
  	int ret = 1;
  
  	preempt_disable();
  	/*
  	 * Same as in percpu_down_read().
  	 */
  	__this_cpu_inc(*sem->read_count);
  	if (unlikely(!rcu_sync_is_idle(&sem->rss)))
  		ret = __percpu_down_read(sem, true); /* 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->rw_sem.dep_map, 0, 1, _RET_IP_);
  
  	return ret;
  }

  static inline void percpu_up_read_preempt_enable(struct percpu_rw_semaphore *sem)

  {
  	/*

  	 * The barrier() prevents the compiler from

  	 * bleeding the critical section out.
  	 */

  	barrier();

  	/*
  	 * Same as in percpu_down_read().
  	 */
  	if (likely(rcu_sync_is_idle(&sem->rss)))
  		__this_cpu_dec(*sem->read_count);
  	else
  		__percpu_up_read(sem); /* Unconditional memory barrier */
  	preempt_enable();
  
  	rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
  }

  static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
  {
  	preempt_disable();
  	percpu_up_read_preempt_enable(sem);
  }

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

  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)->rw_sem)

  #define percpu_rwsem_assert_held(sem)				\
  	lockdep_assert_held(&(sem)->rw_sem)

  static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
  					bool read, unsigned long ip)
  {
  	lock_release(&sem->rw_sem.dep_map, 1, ip);
  #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  	if (!read)
  		sem->rw_sem.owner = NULL;
  #endif
  }
  
  static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
  					bool read, unsigned long ip)
  {
  	lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
  }

  #endif