include/linux/rculist_nulls.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_RCULIST_NULLS_H
   3 #define _LINUX_RCULIST_NULLS_H
   4
   5 #ifdef __KERNEL__
   6
   7 /*
   8  * RCU-protected list version
   9  */
  10 #include <linux/list_nulls.h>
  11 #include <linux/rcupdate.h>
  12
  13 /**
  14  * hlist_nulls_del_init_rcu - deletes entry from hash list with re-initialization
  15  * @n: the element to delete from the hash list.
  16  *
  17  * Note: hlist_nulls_unhashed() on the node return true after this. It is
  18  * useful for RCU based read lockfree traversal if the writer side
  19  * must know if the list entry is still hashed or already unhashed.
  20  *
  21  * In particular, it means that we can not poison the forward pointers
  22  * that may still be used for walking the hash list and we can only
  23  * zero the pprev pointer so list_unhashed() will return true after
  24  * this.
  25  *
  26  * The caller must take whatever precautions are necessary (such as
  27  * holding appropriate locks) to avoid racing with another
  28  * list-mutation primitive, such as hlist_nulls_add_head_rcu() or
  29  * hlist_nulls_del_rcu(), running on this same list.  However, it is
  30  * perfectly legal to run concurrently with the _rcu list-traversal
  31  * primitives, such as hlist_nulls_for_each_entry_rcu().
  32  */
  33 static inline void hlist_nulls_del_init_rcu(struct hlist_nulls_node *n)
  34 {
  35         if (!hlist_nulls_unhashed(n)) {
  36                 __hlist_nulls_del(n);
  37                 n->pprev = NULL;
  38         }
  39 }
  40
  41 #define hlist_nulls_first_rcu(head) \
  42         (*((struct hlist_nulls_node __rcu __force **)&(head)->first))
  43
  44 #define hlist_nulls_next_rcu(node) \
  45         (*((struct hlist_nulls_node __rcu __force **)&(node)->next))
  46
  47 /**
  48  * hlist_nulls_del_rcu - deletes entry from hash list without re-initialization
  49  * @n: the element to delete from the hash list.
  50  *
  51  * Note: hlist_nulls_unhashed() on entry does not return true after this,
  52  * the entry is in an undefined state. It is useful for RCU based
  53  * lockfree traversal.
  54  *
  55  * In particular, it means that we can not poison the forward
  56  * pointers that may still be used for walking the hash list.
  57  *
  58  * The caller must take whatever precautions are necessary
  59  * (such as holding appropriate locks) to avoid racing
  60  * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
  61  * or hlist_nulls_del_rcu(), running on this same list.
  62  * However, it is perfectly legal to run concurrently with
  63  * the _rcu list-traversal primitives, such as
  64  * hlist_nulls_for_each_entry().
  65  */
  66 static inline void hlist_nulls_del_rcu(struct hlist_nulls_node *n)
  67 {
  68         __hlist_nulls_del(n);
  69         n->pprev = LIST_POISON2;
  70 }
  71
  72 /**
  73  * hlist_nulls_add_head_rcu
  74  * @n: the element to add to the hash list.
  75  * @h: the list to add to.
  76  *
  77  * Description:
  78  * Adds the specified element to the specified hlist_nulls,
  79  * while permitting racing traversals.
  80  *
  81  * The caller must take whatever precautions are necessary
  82  * (such as holding appropriate locks) to avoid racing
  83  * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
  84  * or hlist_nulls_del_rcu(), running on this same list.
  85  * However, it is perfectly legal to run concurrently with
  86  * the _rcu list-traversal primitives, such as
  87  * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
  88  * problems on Alpha CPUs.  Regardless of the type of CPU, the
  89  * list-traversal primitive must be guarded by rcu_read_lock().
  90  */
  91 static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
  92                                         struct hlist_nulls_head *h)
  93 {
  94         struct hlist_nulls_node *first = h->first;
  95
  96         n->next = first;
  97         n->pprev = &h->first;
  98         rcu_assign_pointer(hlist_nulls_first_rcu(h), n);
  99         if (!is_a_nulls(first))
 100                 first->pprev = &n->next;
 101 }
 102
 103 /**
 104  * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
 105  * @tpos:       the type * to use as a loop cursor.
 106  * @pos:        the &struct hlist_nulls_node to use as a loop cursor.
 107  * @head:       the head for your list.
 108  * @member:     the name of the hlist_nulls_node within the struct.
 109  *
 110  * The barrier() is needed to make sure compiler doesn't cache first element [1],
 111  * as this loop can be restarted [2]
 112  * [1] Documentation/atomic_ops.txt around line 114
 113  * [2] Documentation/RCU/rculist_nulls.txt around line 146
 114  */
 115 #define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member)                 \
 116         for (({barrier();}),                                                    \
 117              pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));            \
 118                 (!is_a_nulls(pos)) &&                                           \
 119                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
 120                 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
 121
 122 /**
 123  * hlist_nulls_for_each_entry_safe -
 124  *   iterate over list of given type safe against removal of list entry
 125  * @tpos:       the type * to use as a loop cursor.
 126  * @pos:        the &struct hlist_nulls_node to use as a loop cursor.
 127  * @head:       the head for your list.
 128  * @member:     the name of the hlist_nulls_node within the struct.
 129  */
 130 #define hlist_nulls_for_each_entry_safe(tpos, pos, head, member)                \
 131         for (({barrier();}),                                                    \
 132              pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));            \
 133                 (!is_a_nulls(pos)) &&                                           \
 134                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member);        \
 135                    pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)); 1; });)
 136 #endif
 137 #endif