/* 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>

  
  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);

  static inline void percpu_down_read(struct percpu_rw_semaphore *sem)

  {
  	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); /* Unconditional memory barrier */

  	/*

  	 * The preempt_enable() prevents the compiler from

  	 * bleeding the critical section out.
  	 */

  	preempt_enable();
  }

  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); /* 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 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)
  #define percpu_rwsem_assert_held(sem)	lockdep_assert_held(sem)

  static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
  					bool read, 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