LXR linux/include/linux/rculist

   1#ifndef _LINUX_RCULIST_NULLS_H
   2#define _LINUX_RCULIST_NULLS_H
   3
   4#ifdef __KERNEL__
   5
   6/*
   7 * RCU-protected list version
   8 */
   9#include <linux/list_nulls.h>
  10#include <linux/rcupdate.h>
  11
  12/**
  13 * hlist_nulls_del_init_rcu - deletes entry from hash list with re-initialization
  14 * @n: the element to delete from the hash list.
  15 *
  16 * Note: hlist_nulls_unhashed() on the node return true after this. It is
  17 * useful for RCU based read lockfree traversal if the writer side
  18 * must know if the list entry is still hashed or already unhashed.
  19 *
  20 * In particular, it means that we can not poison the forward pointers
  21 * that may still be used for walking the hash list and we can only
  22 * zero the pprev pointer so list_unhashed() will return true after
  23 * this.
  24 *
  25 * The caller must take whatever precautions are necessary (such as
  26 * holding appropriate locks) to avoid racing with another
  27 * list-mutation primitive, such as hlist_nulls_add_head_rcu() or
  28 * hlist_nulls_del_rcu(), running on this same list.  However, it is
  29 * perfectly legal to run concurrently with the _rcu list-traversal
  30 * primitives, such as hlist_nulls_for_each_entry_rcu().
  31 */
  32static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
  33{
  34        if (!hlist_nulls_unhashed(n)) {
  35                __hlist_nulls_del(n);
  36                n->pprev = NULL;
  37        }
  38}
  39
  40/**
  41 * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
  42 * @n: the element to delete from the hash list.
  43 *
  44 * Note: hlist_nulls_unhashed() on entry does not return true after this,
  45 * the entry is in an undefined state. It is useful for RCU based
  46 * lockfree traversal.
  47 *
  48 * In particular, it means that we can not poison the forward
  49 * pointers that may still be used for walking the hash list.
  50 *
  51 * The caller must take whatever precautions are necessary
  52 * (such as holding appropriate locks) to avoid racing
  53 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
  54 * or hlist_nulls_del_rcu(), running on this same list.
  55 * However, it is perfectly legal to run concurrently with
  56 * the _rcu list-traversal primitives, such as
  57 * hlist_nulls_for_each_entry().
  58 */
  59static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
  60{
  61        __hlist_nulls_del(n);
  62        n->pprev = LIST_POISON2;
  63}
  64
  65/**
  66 * hlist_nulls_add_head_rcu
  67 * @n: the element to add to the hash list.
  68 * @h: the list to add to.
  69 *
  70 * Description:
  71 * Adds the specified element to the specified hlist_nulls,
  72 * while permitting racing traversals.
  73 *
  74 * The caller must take whatever precautions are necessary
  75 * (such as holding appropriate locks) to avoid racing
  76 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
  77 * or hlist_nulls_del_rcu(), running on this same list.
  78 * However, it is perfectly legal to run concurrently with
  79 * the _rcu list-traversal primitives, such as
  80 * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
  81 * problems on Alpha CPUs.  Regardless of the type of CPU, the
  82 * list-traversal primitive must be guarded by rcu_read_lock().
  83 */
  84static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
  85                                        struct hlist_nulls_head *h)
  86{
  87        struct hlist_nulls_node *first = h->first;
  88
  89        n->next = first;
  90        n->pprev = &h->first;
  91        rcu_assign_pointer(h->first, n);
  92        if (!is_a_nulls(first))
  93                first->pprev = &n->next;
  94}
  95/**
  96 * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
  97 * @tpos:       the type * to use as a loop cursor.
  98 * @pos:        the &struct hlist_nulls_node to use as a loop cursor.
  99 * @head:       the head for your list.
 100 * @member:     the name of the hlist_nulls_node within the struct.
 101 *
 102 */
 103#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member) \
 104        for (pos = rcu_dereference((head)->first);                       \
 105                (!is_a_nulls(pos)) &&                   \
 106                ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
 107                pos = rcu_dereference(pos->next))
 108
 109#endif
 110#endif
 111