include/linux/rculist_bl.h

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 #ifndef _LINUX_RCULIST_BL_H
   3 #define _LINUX_RCULIST_BL_H
   4
   5 /*
   6  * RCU-protected bl list version. See include/linux/list_bl.h.
   7  */
   8 #include <linux/list_bl.h>
   9 #include <linux/rcupdate.h>
  10
  11 static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
  12                                         struct hlist_bl_node *n)
  13 {
  14         LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
  15         LIST_BL_BUG_ON(((unsigned long)h->first & LIST_BL_LOCKMASK) !=
  16                                                         LIST_BL_LOCKMASK);
  17         rcu_assign_pointer(h->first,
  18                 (struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK));
  19 }
  20
  21 static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
  22 {
  23         return (struct hlist_bl_node *)
  24                 ((unsigned long)rcu_dereference_check(h->first, hlist_bl_is_locked(h)) & ~LIST_BL_LOCKMASK);
  25 }
  26
  27 /**
  28  * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
  29  * @n: the element to delete from the hash list.
  30  *
  31  * Note: hlist_bl_unhashed() on entry does not return true after this,
  32  * the entry is in an undefined state. It is useful for RCU based
  33  * lockfree traversal.
  34  *
  35  * In particular, it means that we can not poison the forward
  36  * pointers that may still be used for walking the hash list.
  37  *
  38  * The caller must take whatever precautions are necessary
  39  * (such as holding appropriate locks) to avoid racing
  40  * with another list-mutation primitive, such as hlist_bl_add_head_rcu()
  41  * or hlist_bl_del_rcu(), running on this same list.
  42  * However, it is perfectly legal to run concurrently with
  43  * the _rcu list-traversal primitives, such as
  44  * hlist_bl_for_each_entry().
  45  */
  46 static inline void hlist_bl_del_rcu(struct hlist_bl_node *n)
  47 {
  48         __hlist_bl_del(n);
  49         n->pprev = LIST_POISON2;
  50 }
  51
  52 /**
  53  * hlist_bl_add_head_rcu
  54  * @n: the element to add to the hash list.
  55  * @h: the list to add to.
  56  *
  57  * Description:
  58  * Adds the specified element to the specified hlist_bl,
  59  * while permitting racing traversals.
  60  *
  61  * The caller must take whatever precautions are necessary
  62  * (such as holding appropriate locks) to avoid racing
  63  * with another list-mutation primitive, such as hlist_bl_add_head_rcu()
  64  * or hlist_bl_del_rcu(), running on this same list.
  65  * However, it is perfectly legal to run concurrently with
  66  * the _rcu list-traversal primitives, such as
  67  * hlist_bl_for_each_entry_rcu(), used to prevent memory-consistency
  68  * problems on Alpha CPUs.  Regardless of the type of CPU, the
  69  * list-traversal primitive must be guarded by rcu_read_lock().
  70  */
  71 static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
  72                                         struct hlist_bl_head *h)
  73 {
  74         struct hlist_bl_node *first;
  75
  76         /* don't need hlist_bl_first_rcu because we're under lock */
  77         first = hlist_bl_first(h);
  78
  79         n->next = first;
  80         if (first)
  81                 first->pprev = &n->next;
  82         n->pprev = &h->first;
  83
  84         /* need _rcu because we can have concurrent lock free readers */
  85         hlist_bl_set_first_rcu(h, n);
  86 }
  87 /**
  88  * hlist_bl_for_each_entry_rcu - iterate over rcu list of given type
  89  * @tpos:       the type * to use as a loop cursor.
  90  * @pos:        the &struct hlist_bl_node to use as a loop cursor.
  91  * @head:       the head for your list.
  92  * @member:     the name of the hlist_bl_node within the struct.
  93  *
  94  */
  95 #define hlist_bl_for_each_entry_rcu(tpos, pos, head, member)            \
  96         for (pos = hlist_bl_first_rcu(head);                            \
  97                 pos &&                                                  \
  98                 ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
  99                 pos = rcu_dereference_raw(pos->next))
 100
 101 #endif