text: /* SPDX-License-Identifier: GPL-2.0 */
  #ifndef _LINUX_RCULIST_BL_H
  #define _LINUX_RCULIST_BL_H
  
  /*
   * RCU-protected bl list version. See include/linux/list_bl.h.
   */
  #include <linux/list_bl.h>
  #include <linux/rcupdate.h>
  
  static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
  					struct hlist_bl_node *n)
  {
  	LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
  	LIST_BL_BUG_ON(((unsigned long)h->first & LIST_BL_LOCKMASK) !=
  							LIST_BL_LOCKMASK);
  	rcu_assign_pointer(h->first,
  		(struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK));
  }
  
  static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
  {
  	return (struct hlist_bl_node *)
  		((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
  }
  
  /**
   * hlist_bl_del_init_rcu - deletes entry from hash list with re-initialization
   * @n: the element to delete from the hash list.
   *
   * Note: hlist_bl_unhashed() on the node returns 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_bl_add_head_rcu() or
   * hlist_bl_del_rcu(), running on this same list.  However, it is
   * perfectly legal to run concurrently with the _rcu list-traversal
   * primitives, such as hlist_bl_for_each_entry_rcu().
   */
  static inline void hlist_bl_del_init_rcu(struct hlist_bl_node *n)
  {
  	if (!hlist_bl_unhashed(n)) {
  		__hlist_bl_del(n);
  		n->pprev = NULL;
  	}
  }
  
  /**
   * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
   * @n: the element to delete from the hash list.
   *
   * Note: hlist_bl_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_bl_add_head_rcu()
   * or hlist_bl_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * hlist_bl_for_each_entry().
   */
  static inline void hlist_bl_del_rcu(struct hlist_bl_node *n)
  {
  	__hlist_bl_del(n);
  	n->pprev = LIST_POISON2;
  }
  
  /**
   * hlist_bl_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_bl,
   * 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_bl_add_head_rcu()
   * or hlist_bl_del_rcu(), running on this same list.
   * However, it is perfectly legal to run concurrently with
   * the _rcu list-traversal primitives, such as
   * hlist_bl_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_bl_add_head_rcu(struct hlist_bl_node *n,
  					struct hlist_bl_head *h)
  {
  	struct hlist_bl_node *first;
  
  	/* don't need hlist_bl_first_rcu because we're under lock */
  	first = hlist_bl_first(h);
  
  	n->next = first;
  	if (first)
  		first->pprev = &n->next;
  	n->pprev = &h->first;
  
  	/* need _rcu because we can have concurrent lock free readers */
  	hlist_bl_set_first_rcu(h, n);
  }
  /**
   * hlist_bl_for_each_entry_rcu - iterate over rcu list of given type
   * @tpos:	the type * to use as a loop cursor.
   * @pos:	the &struct hlist_bl_node to use as a loop cursor.
   * @head:	the head for your list.
   * @member:	the name of the hlist_bl_node within the struct.
   *
   */
  #define hlist_bl_for_each_entry_rcu(tpos, pos, head, member)		\
  	for (pos = hlist_bl_first_rcu(head);				\
  		pos &&							\
  		({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
  		pos = rcu_dereference_raw(pos->next))
  
  #endif
  