/* SPDX-License-Identifier: GPL-2.0 */

  #ifndef _LINUX_RCULIST_H
  #define _LINUX_RCULIST_H
  
  #ifdef __KERNEL__
  
  /*
   * RCU-protected list version
   */
  #include <linux/list.h>

  #include <linux/rcupdate.h>

  
  /*

   * Why is there no list_empty_rcu()?  Because list_empty() serves this
   * purpose.  The list_empty() function fetches the RCU-protected pointer
   * and compares it to the address of the list head, but neither dereferences
   * this pointer itself nor provides this pointer to the caller.  Therefore,
   * it is not necessary to use rcu_dereference(), so that list_empty() can
   * be used anywhere you would want to use a list_empty_rcu().
   */
  
  /*

   * INIT_LIST_HEAD_RCU - Initialize a list_head visible to RCU readers
   * @list: list to be initialized
   *
   * You should instead use INIT_LIST_HEAD() for normal initialization and
   * cleanup tasks, when readers have no access to the list being initialized.
   * However, if the list being initialized is visible to readers, you
   * need to keep the compiler from being too mischievous.
   */
  static inline void INIT_LIST_HEAD_RCU(struct list_head *list)
  {

  	WRITE_ONCE(list->next, list);
  	WRITE_ONCE(list->prev, list);

  }
  
  /*

   * return the ->next pointer of a list_head in an rcu safe
   * way, we must not access it directly
   */
  #define list_next_rcu(list)	(*((struct list_head __rcu **)(&(list)->next)))

  /**
   * list_tail_rcu - returns the prev pointer of the head of the list
   * @head: the head of the list
   *
   * Note: This should only be used with the list header, and even then
   * only if list_del() and similar primitives are not also used on the
   * list header.
   */
  #define list_tail_rcu(head)	(*((struct list_head __rcu **)(&(head)->prev)))

  /*

   * Check during list traversal that we are within an RCU reader
   */
  
  #define check_arg_count_one(dummy)
  
  #ifdef CONFIG_PROVE_RCU_LIST
  #define __list_check_rcu(dummy, cond, extra...)				\
  	({								\
  	check_arg_count_one(extra);					\

  	RCU_LOCKDEP_WARN(!(cond) && !rcu_read_lock_any_held(),		\

  			 "RCU-list traversed in non-reader section!");	\

  	})

  
  #define __list_check_srcu(cond)					 \
  	({								 \
  	RCU_LOCKDEP_WARN(!(cond),					 \
  		"RCU-list traversed without holding the required lock!");\
  	})

  #else
  #define __list_check_rcu(dummy, cond, extra...)				\
  	({ check_arg_count_one(extra); })

  
  #define __list_check_srcu(cond) ({ })

  #endif
  
  /*

   * Insert a new entry between two known consecutive entries.
   *
   * This is only for internal list manipulation where we know
   * the prev/next entries already!
   */
  static inline void __list_add_rcu(struct list_head *new,
  		struct list_head *prev, struct list_head *next)
  {

  	if (!__list_add_valid(new, prev, next))
  		return;

  	new->next = next;
  	new->prev = prev;

  	rcu_assign_pointer(list_next_rcu(prev), new);

  	next->prev = new;

  }
  
  /**
   * list_add_rcu - add a new entry to rcu-protected list
   * @new: new entry to be added
   * @head: list head to add it after
   *
   * Insert a new entry after the specified head.
   * This is good for implementing stacks.
   *
   * The caller must take whatever precautions are necessary
   * (such as holding appropriate locks) to avoid racing
   * with another list-mutation primitive, such as list_add_rcu()
   * or list_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * list_for_each_entry_rcu().
   */
  static inline void list_add_rcu(struct list_head *new, struct list_head *head)
  {
  	__list_add_rcu(new, head, head->next);
  }
  
  /**
   * list_add_tail_rcu - add a new entry to rcu-protected list
   * @new: new entry to be added
   * @head: list head to add it before
   *
   * Insert a new entry before the specified head.
   * This is useful for implementing queues.
   *
   * The caller must take whatever precautions are necessary
   * (such as holding appropriate locks) to avoid racing
   * with another list-mutation primitive, such as list_add_tail_rcu()
   * or list_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * list_for_each_entry_rcu().
   */
  static inline void list_add_tail_rcu(struct list_head *new,
  					struct list_head *head)
  {
  	__list_add_rcu(new, head->prev, head);
  }
  
  /**
   * list_del_rcu - deletes entry from list without re-initialization
   * @entry: the element to delete from the list.
   *
   * Note: list_empty() on entry does not return true after this,
   * the entry is in an undefined state. It is useful for RCU based
   * lockfree traversal.
   *
   * In particular, it means that we can not poison the forward
   * pointers that may still be used for walking the list.
   *
   * The caller must take whatever precautions are necessary
   * (such as holding appropriate locks) to avoid racing
   * with another list-mutation primitive, such as list_del_rcu()
   * or list_add_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * list_for_each_entry_rcu().
   *
   * Note that the caller is not permitted to immediately free
   * the newly deleted entry.  Instead, either synchronize_rcu()
   * or call_rcu() must be used to defer freeing until an RCU
   * grace period has elapsed.
   */
  static inline void list_del_rcu(struct list_head *entry)
  {

  	__list_del_entry(entry);

  	entry->prev = LIST_POISON2;
  }
  
  /**

   * hlist_del_init_rcu - deletes entry from hash list with re-initialization
   * @n: the element to delete from the hash list.
   *
   * Note: list_unhashed() on the node return true after this. It is
   * useful for RCU based read lockfree traversal if the writer side
   * must know if the list entry is still hashed or already unhashed.
   *
   * In particular, it means that we can not poison the forward pointers
   * that may still be used for walking the hash list and we can only
   * zero the pprev pointer so list_unhashed() will return true after
   * this.
   *
   * The caller must take whatever precautions are necessary (such as
   * holding appropriate locks) to avoid racing with another
   * list-mutation primitive, such as hlist_add_head_rcu() or
   * hlist_del_rcu(), running on this same list.  However, it is
   * perfectly legal to run concurrently with the _rcu list-traversal
   * primitives, such as hlist_for_each_entry_rcu().
   */
  static inline void hlist_del_init_rcu(struct hlist_node *n)
  {
  	if (!hlist_unhashed(n)) {
  		__hlist_del(n);

  		WRITE_ONCE(n->pprev, NULL);

  	}
  }
  
  /**

   * list_replace_rcu - replace old entry by new one
   * @old : the element to be replaced
   * @new : the new element to insert
   *
   * The @old entry will be replaced with the @new entry atomically.
   * Note: @old should not be empty.
   */
  static inline void list_replace_rcu(struct list_head *old,
  				struct list_head *new)
  {
  	new->next = old->next;
  	new->prev = old->prev;

  	rcu_assign_pointer(list_next_rcu(new->prev), new);

  	new->next->prev = new;

  	old->prev = LIST_POISON2;
  }
  
  /**

   * __list_splice_init_rcu - join an RCU-protected list into an existing list.

   * @list:	the RCU-protected list to splice

   * @prev:	points to the last element of the existing list
   * @next:	points to the first element of the existing list

   * @sync:	synchronize_rcu, synchronize_rcu_expedited, ...

   *

   * The list pointed to by @prev and @next can be RCU-read traversed
   * concurrently with this function.

   *
   * Note that this function blocks.
   *

   * Important note: the caller must take whatever action is necessary to prevent
   * any other updates to the existing list.  In principle, it is possible to
   * modify the list as soon as sync() begins execution. If this sort of thing
   * becomes necessary, an alternative version based on call_rcu() could be
   * created.  But only if -really- needed -- there is no shortage of RCU API
   * members.

   */

  static inline void __list_splice_init_rcu(struct list_head *list,
  					  struct list_head *prev,
  					  struct list_head *next,
  					  void (*sync)(void))

  {
  	struct list_head *first = list->next;
  	struct list_head *last = list->prev;

  	/*
  	 * "first" and "last" tracking list, so initialize it.  RCU readers
  	 * have access to this list, so we must use INIT_LIST_HEAD_RCU()
  	 * instead of INIT_LIST_HEAD().
  	 */

  	INIT_LIST_HEAD_RCU(list);

  
  	/*
  	 * At this point, the list body still points to the source list.
  	 * Wait for any readers to finish using the list before splicing
  	 * the list body into the new list.  Any new readers will see
  	 * an empty list.
  	 */
  
  	sync();

  	ASSERT_EXCLUSIVE_ACCESS(*first);
  	ASSERT_EXCLUSIVE_ACCESS(*last);

  
  	/*
  	 * Readers are finished with the source list, so perform splice.
  	 * The order is important if the new list is global and accessible
  	 * to concurrent RCU readers.  Note that RCU readers are not
  	 * permitted to traverse the prev pointers without excluding
  	 * this function.
  	 */

  	last->next = next;
  	rcu_assign_pointer(list_next_rcu(prev), first);
  	first->prev = prev;
  	next->prev = last;
  }
  
  /**
   * list_splice_init_rcu - splice an RCU-protected list into an existing list,
   *                        designed for stacks.
   * @list:	the RCU-protected list to splice
   * @head:	the place in the existing list to splice the first list into

   * @sync:	synchronize_rcu, synchronize_rcu_expedited, ...

   */
  static inline void list_splice_init_rcu(struct list_head *list,
  					struct list_head *head,
  					void (*sync)(void))
  {
  	if (!list_empty(list))
  		__list_splice_init_rcu(list, head, head->next, sync);
  }
  
  /**
   * list_splice_tail_init_rcu - splice an RCU-protected list into an existing
   *                             list, designed for queues.
   * @list:	the RCU-protected list to splice
   * @head:	the place in the existing list to splice the first list into

   * @sync:	synchronize_rcu, synchronize_rcu_expedited, ...

   */
  static inline void list_splice_tail_init_rcu(struct list_head *list,
  					     struct list_head *head,
  					     void (*sync)(void))
  {
  	if (!list_empty(list))
  		__list_splice_init_rcu(list, head->prev, head, sync);

  }

  /**
   * list_entry_rcu - get the struct for this entry
   * @ptr:        the &struct list_head pointer.
   * @type:       the type of the struct this is embedded in.

   * @member:     the name of the list_head within the struct.

   *
   * This primitive may safely run concurrently with the _rcu list-mutation
   * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
   */
  #define list_entry_rcu(ptr, type, member) \

  	container_of(READ_ONCE(ptr), type, member)

  /*

   * Where are list_empty_rcu() and list_first_entry_rcu()?
   *
   * Implementing those functions following their counterparts list_empty() and
   * list_first_entry() is not advisable because they lead to subtle race
   * conditions as the following snippet shows:
   *
   * if (!list_empty_rcu(mylist)) {
   *	struct foo *bar = list_first_entry_rcu(mylist, struct foo, list_member);
   *	do_something(bar);
   * }
   *
   * The list may not be empty when list_empty_rcu checks it, but it may be when
   * list_first_entry_rcu rereads the ->next pointer.
   *
   * Rereading the ->next pointer is not a problem for list_empty() and
   * list_first_entry() because they would be protected by a lock that blocks
   * writers.
   *
   * See list_first_or_null_rcu for an alternative.
   */
  
  /**
   * list_first_or_null_rcu - get the first element from a list

   * @ptr:        the list head to take the element from.
   * @type:       the type of the struct this is embedded in.

   * @member:     the name of the list_head within the struct.

   *

   * Note that if the list is empty, it returns NULL.

   *
   * This primitive may safely run concurrently with the _rcu list-mutation
   * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
   */

  #define list_first_or_null_rcu(ptr, type, member) \

  ({ \
  	struct list_head *__ptr = (ptr); \

  	struct list_head *__next = READ_ONCE(__ptr->next); \

  	likely(__ptr != __next) ? list_entry_rcu(__next, type, member) : NULL; \
  })

  /**

   * list_next_or_null_rcu - get the first element from a list
   * @head:	the head for the list.
   * @ptr:        the list head to take the next element from.
   * @type:       the type of the struct this is embedded in.
   * @member:     the name of the list_head within the struct.
   *
   * Note that if the ptr is at the end of the list, NULL is returned.
   *
   * This primitive may safely run concurrently with the _rcu list-mutation
   * primitives such as list_add_rcu() as long as it's guarded by rcu_read_lock().
   */
  #define list_next_or_null_rcu(head, ptr, type, member) \
  ({ \
  	struct list_head *__head = (head); \
  	struct list_head *__ptr = (ptr); \
  	struct list_head *__next = READ_ONCE(__ptr->next); \
  	likely(__next != __head) ? list_entry_rcu(__next, type, \
  						  member) : NULL; \
  })
  
  /**

   * list_for_each_entry_rcu	-	iterate over rcu list of given type
   * @pos:	the type * to use as a loop cursor.
   * @head:	the head for your list.

   * @member:	the name of the list_head within the struct.

   * @cond:	optional lockdep expression if called from non-RCU protection.

   *
   * This list-traversal primitive may safely run concurrently with
   * the _rcu list-mutation primitives such as list_add_rcu()
   * as long as the traversal is guarded by rcu_read_lock().
   */

  #define list_for_each_entry_rcu(pos, head, member, cond...)		\
  	for (__list_check_rcu(dummy, ## cond, 0),			\
  	     pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
  		&pos->member != (head);					\

  		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))

  /**

   * list_for_each_entry_srcu	-	iterate over rcu list of given type
   * @pos:	the type * to use as a loop cursor.
   * @head:	the head for your list.
   * @member:	the name of the list_head within the struct.
   * @cond:	lockdep expression for the lock required to traverse the list.
   *
   * This list-traversal primitive may safely run concurrently with
   * the _rcu list-mutation primitives such as list_add_rcu()
   * as long as the traversal is guarded by srcu_read_lock().
   * The lockdep expression srcu_read_lock_held() can be passed as the
   * cond argument from read side.
   */
  #define list_for_each_entry_srcu(pos, head, member, cond)		\
  	for (__list_check_srcu(cond),					\
  	     pos = list_entry_rcu((head)->next, typeof(*pos), member);	\
  		&pos->member != (head);					\
  		pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
  
  /**

   * list_entry_lockless - get the struct for this entry
   * @ptr:        the &struct list_head pointer.
   * @type:       the type of the struct this is embedded in.
   * @member:     the name of the list_head within the struct.
   *

   * This primitive may safely run concurrently with the _rcu
   * list-mutation primitives such as list_add_rcu(), but requires some
   * implicit RCU read-side guarding.  One example is running within a special
   * exception-time environment where preemption is disabled and where lockdep
   * cannot be invoked.  Another example is when items are added to the list,
   * but never deleted.

   */
  #define list_entry_lockless(ptr, type, member) \

  	container_of((typeof(ptr))READ_ONCE(ptr), type, member)

  
  /**
   * list_for_each_entry_lockless - iterate over rcu list of given type
   * @pos:	the type * to use as a loop cursor.
   * @head:	the head for your list.
   * @member:	the name of the list_struct within the struct.
   *

   * This primitive may safely run concurrently with the _rcu
   * list-mutation primitives such as list_add_rcu(), but requires some
   * implicit RCU read-side guarding.  One example is running within a special
   * exception-time environment where preemption is disabled and where lockdep
   * cannot be invoked.  Another example is when items are added to the list,
   * but never deleted.

   */
  #define list_for_each_entry_lockless(pos, head, member) \
  	for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \
  	     &pos->member != (head); \
  	     pos = list_entry_lockless(pos->member.next, typeof(*pos), member))
  
  /**

   * list_for_each_entry_continue_rcu - continue iteration over list of given type
   * @pos:	the type * to use as a loop cursor.
   * @head:	the head for your list.

   * @member:	the name of the list_head within the struct.

   *
   * Continue to iterate over list of given type, continuing after

   * the current position which must have been in the list when the RCU read
   * lock was taken.
   * This would typically require either that you obtained the node from a
   * previous walk of the list in the same RCU read-side critical section, or
   * that you held some sort of non-RCU reference (such as a reference count)
   * to keep the node alive *and* in the list.
   *
   * This iterator is similar to list_for_each_entry_from_rcu() except
   * this starts after the given position and that one starts at the given
   * position.

   */
  #define list_for_each_entry_continue_rcu(pos, head, member) 		\
  	for (pos = list_entry_rcu(pos->member.next, typeof(*pos), member); \

  	     &pos->member != (head);	\

  	     pos = list_entry_rcu(pos->member.next, typeof(*pos), member))
  
  /**

   * list_for_each_entry_from_rcu - iterate over a list from current point
   * @pos:	the type * to use as a loop cursor.
   * @head:	the head for your list.
   * @member:	the name of the list_node within the struct.
   *
   * Iterate over the tail of a list starting from a given position,
   * which must have been in the list when the RCU read lock was taken.

   * This would typically require either that you obtained the node from a
   * previous walk of the list in the same RCU read-side critical section, or
   * that you held some sort of non-RCU reference (such as a reference count)
   * to keep the node alive *and* in the list.
   *
   * This iterator is similar to list_for_each_entry_continue_rcu() except
   * this starts from the given position and that one starts from the position
   * after the given position.

   */
  #define list_for_each_entry_from_rcu(pos, head, member)			\
  	for (; &(pos)->member != (head);					\
  		pos = list_entry_rcu(pos->member.next, typeof(*(pos)), member))
  
  /**

   * hlist_del_rcu - deletes entry from hash list without re-initialization
   * @n: the element to delete from the hash list.
   *
   * Note: list_unhashed() on entry does not return true after this,
   * the entry is in an undefined state. It is useful for RCU based
   * lockfree traversal.
   *
   * In particular, it means that we can not poison the forward
   * pointers that may still be used for walking the hash list.
   *
   * The caller must take whatever precautions are necessary
   * (such as holding appropriate locks) to avoid racing
   * with another list-mutation primitive, such as hlist_add_head_rcu()
   * or hlist_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * hlist_for_each_entry().
   */
  static inline void hlist_del_rcu(struct hlist_node *n)
  {
  	__hlist_del(n);

  	WRITE_ONCE(n->pprev, LIST_POISON2);

  }
  
  /**
   * hlist_replace_rcu - replace old entry by new one
   * @old : the element to be replaced
   * @new : the new element to insert
   *
   * The @old entry will be replaced with the @new entry atomically.
   */
  static inline void hlist_replace_rcu(struct hlist_node *old,
  					struct hlist_node *new)
  {
  	struct hlist_node *next = old->next;
  
  	new->next = next;

  	WRITE_ONCE(new->pprev, old->pprev);

  	rcu_assign_pointer(*(struct hlist_node __rcu **)new->pprev, new);

  	if (next)

  		WRITE_ONCE(new->next->pprev, &new->next);
  	WRITE_ONCE(old->pprev, LIST_POISON2);

  }

  /**
   * hlists_swap_heads_rcu - swap the lists the hlist heads point to
   * @left:  The hlist head on the left
   * @right: The hlist head on the right
   *
   * The lists start out as [@left  ][node1 ... ] and

   *                        [@right ][node2 ... ]

   * The lists end up as    [@left  ][node2 ... ]
   *                        [@right ][node1 ... ]
   */
  static inline void hlists_swap_heads_rcu(struct hlist_head *left, struct hlist_head *right)
  {
  	struct hlist_node *node1 = left->first;
  	struct hlist_node *node2 = right->first;
  
  	rcu_assign_pointer(left->first, node2);
  	rcu_assign_pointer(right->first, node1);
  	WRITE_ONCE(node2->pprev, &left->first);
  	WRITE_ONCE(node1->pprev, &right->first);
  }

  /*
   * return the first or the next element in an RCU protected hlist
   */
  #define hlist_first_rcu(head)	(*((struct hlist_node __rcu **)(&(head)->first)))
  #define hlist_next_rcu(node)	(*((struct hlist_node __rcu **)(&(node)->next)))
  #define hlist_pprev_rcu(node)	(*((struct hlist_node __rcu **)((node)->pprev)))

  /**
   * hlist_add_head_rcu
   * @n: the element to add to the hash list.
   * @h: the list to add to.
   *
   * Description:
   * Adds the specified element to the specified hlist,
   * while permitting racing traversals.
   *
   * The caller must take whatever precautions are necessary
   * (such as holding appropriate locks) to avoid racing
   * with another list-mutation primitive, such as hlist_add_head_rcu()
   * or hlist_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * hlist_for_each_entry_rcu(), used to prevent memory-consistency
   * problems on Alpha CPUs.  Regardless of the type of CPU, the
   * list-traversal primitive must be guarded by rcu_read_lock().
   */
  static inline void hlist_add_head_rcu(struct hlist_node *n,
  					struct hlist_head *h)
  {
  	struct hlist_node *first = h->first;

  	n->next = first;

  	WRITE_ONCE(n->pprev, &h->first);

  	rcu_assign_pointer(hlist_first_rcu(h), n);

  	if (first)

  		WRITE_ONCE(first->pprev, &n->next);

  }
  
  /**

   * hlist_add_tail_rcu
   * @n: the element to add to the hash list.
   * @h: the list to add to.
   *
   * Description:
   * Adds the specified element to the specified hlist,
   * while permitting racing traversals.
   *
   * The caller must take whatever precautions are necessary
   * (such as holding appropriate locks) to avoid racing
   * with another list-mutation primitive, such as hlist_add_head_rcu()
   * or hlist_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * hlist_for_each_entry_rcu(), used to prevent memory-consistency
   * problems on Alpha CPUs.  Regardless of the type of CPU, the
   * list-traversal primitive must be guarded by rcu_read_lock().
   */
  static inline void hlist_add_tail_rcu(struct hlist_node *n,
  				      struct hlist_head *h)
  {
  	struct hlist_node *i, *last = NULL;

  	/* Note: write side code, so rcu accessors are not needed. */
  	for (i = h->first; i; i = i->next)

  		last = i;
  
  	if (last) {
  		n->next = last->next;

  		WRITE_ONCE(n->pprev, &last->next);

  		rcu_assign_pointer(hlist_next_rcu(last), n);
  	} else {
  		hlist_add_head_rcu(n, h);
  	}
  }
  
  /**

   * hlist_add_before_rcu
   * @n: the new element to add to the hash list.
   * @next: the existing element to add the new element before.
   *
   * Description:
   * Adds the specified element to the specified hlist
   * before the specified node while permitting racing traversals.
   *
   * The caller must take whatever precautions are necessary
   * (such as holding appropriate locks) to avoid racing
   * with another list-mutation primitive, such as hlist_add_head_rcu()
   * or hlist_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * hlist_for_each_entry_rcu(), used to prevent memory-consistency
   * problems on Alpha CPUs.
   */
  static inline void hlist_add_before_rcu(struct hlist_node *n,
  					struct hlist_node *next)
  {

  	WRITE_ONCE(n->pprev, next->pprev);

  	n->next = next;

  	rcu_assign_pointer(hlist_pprev_rcu(n), n);

  	WRITE_ONCE(next->pprev, &n->next);

  }
  
  /**

   * hlist_add_behind_rcu

   * @n: the new element to add to the hash list.

   * @prev: the existing element to add the new element after.

   *
   * Description:
   * Adds the specified element to the specified hlist
   * after the specified node while permitting racing traversals.
   *
   * The caller must take whatever precautions are necessary
   * (such as holding appropriate locks) to avoid racing
   * with another list-mutation primitive, such as hlist_add_head_rcu()
   * or hlist_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * hlist_for_each_entry_rcu(), used to prevent memory-consistency
   * problems on Alpha CPUs.
   */

  static inline void hlist_add_behind_rcu(struct hlist_node *n,
  					struct hlist_node *prev)

  {
  	n->next = prev->next;

  	WRITE_ONCE(n->pprev, &prev->next);

  	rcu_assign_pointer(hlist_next_rcu(prev), n);

  	if (n->next)

  		WRITE_ONCE(n->next->pprev, &n->next);

  }

  #define __hlist_for_each_rcu(pos, head)				\
  	for (pos = rcu_dereference(hlist_first_rcu(head));	\

  	     pos;						\

  	     pos = rcu_dereference(hlist_next_rcu(pos)))

  /**
   * hlist_for_each_entry_rcu - iterate over rcu list of given type

   * @pos:	the type * to use as a loop cursor.

   * @head:	the head for your list.
   * @member:	the name of the hlist_node within the struct.

   * @cond:	optional lockdep expression if called from non-RCU protection.

   *
   * This list-traversal primitive may safely run concurrently with
   * the _rcu list-mutation primitives such as hlist_add_head_rcu()
   * as long as the traversal is guarded by rcu_read_lock().
   */

  #define hlist_for_each_entry_rcu(pos, head, member, cond...)		\
  	for (__list_check_rcu(dummy, ## cond, 0),			\
  	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\

  			typeof(*(pos)), member);			\
  		pos;							\
  		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\

  			&(pos)->member)), typeof(*(pos)), member))
  
  /**
   * hlist_for_each_entry_srcu - iterate over rcu list of given type
   * @pos:	the type * to use as a loop cursor.
   * @head:	the head for your list.
   * @member:	the name of the hlist_node within the struct.
   * @cond:	lockdep expression for the lock required to traverse the list.
   *
   * This list-traversal primitive may safely run concurrently with
   * the _rcu list-mutation primitives such as hlist_add_head_rcu()
   * as long as the traversal is guarded by srcu_read_lock().
   * The lockdep expression srcu_read_lock_held() can be passed as the
   * cond argument from read side.
   */
  #define hlist_for_each_entry_srcu(pos, head, member, cond)		\
  	for (__list_check_srcu(cond),					\
  	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_first_rcu(head)),\
  			typeof(*(pos)), member);			\
  		pos;							\
  		pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(\

  			&(pos)->member)), typeof(*(pos)), member))

  /**

   * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type (for tracing)
   * @pos:	the type * to use as a loop cursor.
   * @head:	the head for your list.
   * @member:	the name of the hlist_node within the struct.
   *
   * This list-traversal primitive may safely run concurrently with
   * the _rcu list-mutation primitives such as hlist_add_head_rcu()
   * as long as the traversal is guarded by rcu_read_lock().
   *
   * This is the same as hlist_for_each_entry_rcu() except that it does
   * not do any RCU debugging or tracing.
   */
  #define hlist_for_each_entry_rcu_notrace(pos, head, member)			\

  	for (pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_first_rcu(head)),\

  			typeof(*(pos)), member);			\
  		pos;							\

  		pos = hlist_entry_safe(rcu_dereference_raw_check(hlist_next_rcu(\

  			&(pos)->member)), typeof(*(pos)), member))
  
  /**

   * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type

   * @pos:	the type * to use as a loop cursor.

   * @head:	the head for your list.
   * @member:	the name of the hlist_node within the struct.
   *
   * This list-traversal primitive may safely run concurrently with
   * the _rcu list-mutation primitives such as hlist_add_head_rcu()
   * as long as the traversal is guarded by rcu_read_lock().
   */

  #define hlist_for_each_entry_rcu_bh(pos, head, member)			\
  	for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_first_rcu(head)),\
  			typeof(*(pos)), member);			\
  		pos;							\
  		pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(\
  			&(pos)->member)), typeof(*(pos)), member))

  
  /**

   * hlist_for_each_entry_continue_rcu - iterate over a hlist continuing after current point

   * @pos:	the type * to use as a loop cursor.

   * @member:	the name of the hlist_node within the struct.
   */

  #define hlist_for_each_entry_continue_rcu(pos, member)			\

  	for (pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu( \
  			&(pos)->member)), typeof(*(pos)), member);	\

  	     pos;							\

  	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(	\
  			&(pos)->member)), typeof(*(pos)), member))

  /**
   * hlist_for_each_entry_continue_rcu_bh - iterate over a hlist continuing after current point

   * @pos:	the type * to use as a loop cursor.

   * @member:	the name of the hlist_node within the struct.
   */

  #define hlist_for_each_entry_continue_rcu_bh(pos, member)		\

  	for (pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(  \
  			&(pos)->member)), typeof(*(pos)), member);	\

  	     pos;							\

  	     pos = hlist_entry_safe(rcu_dereference_bh(hlist_next_rcu(	\
  			&(pos)->member)), typeof(*(pos)), member))

  /**
   * hlist_for_each_entry_from_rcu - iterate over a hlist continuing from current point
   * @pos:	the type * to use as a loop cursor.
   * @member:	the name of the hlist_node within the struct.
   */
  #define hlist_for_each_entry_from_rcu(pos, member)			\
  	for (; pos;							\

  	     pos = hlist_entry_safe(rcu_dereference_raw(hlist_next_rcu(	\
  			&(pos)->member)), typeof(*(pos)), member))

  #endif	/* __KERNEL__ */
  #endif