linux/include/linux/rculist_nulls.h
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   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#define hlist_nulls_first_rcu(head) \
  41        (*((struct hlist_nulls_node __rcu __force **)&(head)->first))
  42
  43#define hlist_nulls_next_rcu(node) \
  44        (*((struct hlist_nulls_node __rcu __force **)&(node)->next))
  45
  46/**
  47 * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
  48 * @n: the element to delete from the hash list.
  49 *
  50 * Note: hlist_nulls_unhashed() on entry does not return true after this,
  51 * the entry is in an undefined state. It is useful for RCU based
  52 * lockfree traversal.
  53 *
  54 * In particular, it means that we can not poison the forward
  55 * pointers that may still be used for walking the hash list.
  56 *
  57 * The caller must take whatever precautions are necessary
  58 * (such as holding appropriate locks) to avoid racing
  59 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
  60 * or hlist_nulls_del_rcu(), running on this same list.
  61 * However, it is perfectly legal to run concurrently with
  62 * the _rcu list-traversal primitives, such as
  63 * hlist_nulls_for_each_entry().
  64 */
  65static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
  66{
  67        __hlist_nulls_del(n);
  68        n->pprev = LIST_POISON2;
  69}
  70
  71/**
  72 * hlist_nulls_add_head_rcu
  73 * @n: the element to add to the hash list.
  74 * @h: the list to add to.
  75 *
  76 * Description:
  77 * Adds the specified element to the specified hlist_nulls,
  78 * while permitting racing traversals.
  79 *
  80 * The caller must take whatever precautions are necessary
  81 * (such as holding appropriate locks) to avoid racing
  82 * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
  83 * or hlist_nulls_del_rcu(), running on this same list.
  84 * However, it is perfectly legal to run concurrently with
  85 * the _rcu list-traversal primitives, such as
  86 * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
  87 * problems on Alpha CPUs.  Regardless of the type of CPU, the
  88 * list-traversal primitive must be guarded by rcu_read_lock().
  89 */
  90static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
  91                                        struct hlist_nulls_head *h)
  92{
  93        struct hlist_nulls_node *first = h->first;
  94
  95        n->next = first;
  96        n->pprev = &h->first;
  97        rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
  98        if (!is_a_nulls(first))
  99                first->pprev = &n->next;
 100}
 101/**
 102 * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
 103 * @tpos:       the type * to use as a loop cursor.
 104 * @pos:        the &struct hlist_nulls_node to use as a loop cursor.
 105 * @head:       the head for your list.
 106 * @member:     the name of the hlist_nulls_node within the struct.
 107 *
 108 */
 109#define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member)                 \
 110        for (pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));            \
 111                (!is_a_nulls(pos)) &&                                           \
 112                ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
 113                pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
 114
 115#endif
 116#endif
 117
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