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 #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  */
  65 static 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  */
  90 static 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  * The barrier() is needed to make sure compiler doesn't cache first element [1],
 109  * as this loop can be restarted [2]
 110  * [1] Documentation/atomic_ops.txt around line 114
 111  * [2] Documentation/RCU/rculist_nulls.txt around line 146
 112  */
 113 #define hlist_nulls_for_each_entry_rcu(tpos, pos, head, member)                 \
 114         for (({barrier();}),                                                    \
 115              pos = rcu_dereference_raw(hlist_nulls_first_rcu(head));            \
 116                 (!is_a_nulls(pos)) &&                                           \
 117                 ({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1; }); \
 118                 pos = rcu_dereference_raw(hlist_nulls_next_rcu(pos)))
 119
 120 #endif
 121 #endif