include/linux/rculist_nulls.h

   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  */
  32 static 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  */
  59 static 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  */
  84 static 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