include/linux/rculist_bl.h

   1 #ifndef _LINUX_RCULIST_BL_H
   2 #define _LINUX_RCULIST_BL_H
   3
   4 /*
   5  * RCU-protected bl list version. See include/linux/list_bl.h.
   6  */
   7 #include <linux/list_bl.h>
   8 #include <linux/rcupdate.h>
   9
  10 static inline void hlist_bl_set_first_rcu(struct hlist_bl_head *h,
  11                                         struct hlist_bl_node *n)
  12 {
  13         LIST_BL_BUG_ON((unsigned long)n & LIST_BL_LOCKMASK);
  14         LIST_BL_BUG_ON(((unsigned long)h->first & LIST_BL_LOCKMASK) !=
  15                                                         LIST_BL_LOCKMASK);
  16         rcu_assign_pointer(h->first,
  17                 (struct hlist_bl_node *)((unsigned long)n | LIST_BL_LOCKMASK));
  18 }
  19
  20 static inline struct hlist_bl_node *hlist_bl_first_rcu(struct hlist_bl_head *h)
  21 {
  22         return (struct hlist_bl_node *)
  23                 ((unsigned long)rcu_dereference(h->first) & ~LIST_BL_LOCKMASK);
  24 }
  25
  26 /**
  27  * hlist_bl_del_init_rcu - deletes entry from hash list with re-initialization
  28  * @n: the element to delete from the hash list.
  29  *
  30  * Note: hlist_bl_unhashed() on the node returns true after this. It is
  31  * useful for RCU based read lockfree traversal if the writer side
  32  * must know if the list entry is still hashed or already unhashed.
  33  *
  34  * In particular, it means that we can not poison the forward pointers
  35  * that may still be used for walking the hash list and we can only
  36  * zero the pprev pointer so list_unhashed() will return true after
  37  * this.
  38  *
  39  * The caller must take whatever precautions are necessary (such as
  40  * holding appropriate locks) to avoid racing with another
  41  * list-mutation primitive, such as hlist_bl_add_head_rcu() or
  42  * hlist_bl_del_rcu(), running on this same list.  However, it is
  43  * perfectly legal to run concurrently with the _rcu list-traversal
  44  * primitives, such as hlist_bl_for_each_entry_rcu().
  45  */
  46 static inline void hlist_bl_del_init_rcu(struct hlist_bl_node *n)
  47 {
  48         if (!hlist_bl_unhashed(n)) {
  49                 __hlist_bl_del(n);
  50                 n->pprev = NULL;
  51         }
  52 }
  53
  54 /**
  55  * hlist_bl_del_rcu - deletes entry from hash list without re-initialization
  56  * @n: the element to delete from the hash list.
  57  *
  58  * Note: hlist_bl_unhashed() on entry does not return true after this,
  59  * the entry is in an undefined state. It is useful for RCU based
  60  * lockfree traversal.
  61  *
  62  * In particular, it means that we can not poison the forward
  63  * pointers that may still be used for walking the hash list.
  64  *
  65  * The caller must take whatever precautions are necessary
  66  * (such as holding appropriate locks) to avoid racing
  67  * with another list-mutation primitive, such as hlist_bl_add_head_rcu()
  68  * or hlist_bl_del_rcu(), running on this same list.
  69  * However, it is perfectly legal to run concurrently with
  70  * the _rcu list-traversal primitives, such as
  71  * hlist_bl_for_each_entry().
  72  */
  73 static inline void hlist_bl_del_rcu(struct hlist_bl_node *n)
  74 {
  75         __hlist_bl_del(n);
  76         n->pprev = LIST_POISON2;
  77 }
  78
  79 /**
  80  * hlist_bl_add_head_rcu
  81  * @n: the element to add to the hash list.
  82  * @h: the list to add to.
  83  *
  84  * Description:
  85  * Adds the specified element to the specified hlist_bl,
  86  * while permitting racing traversals.
  87  *
  88  * The caller must take whatever precautions are necessary
  89  * (such as holding appropriate locks) to avoid racing
  90  * with another list-mutation primitive, such as hlist_bl_add_head_rcu()
  91  * or hlist_bl_del_rcu(), running on this same list.
  92  * However, it is perfectly legal to run concurrently with
  93  * the _rcu list-traversal primitives, such as
  94  * hlist_bl_for_each_entry_rcu(), used to prevent memory-consistency
  95  * problems on Alpha CPUs.  Regardless of the type of CPU, the
  96  * list-traversal primitive must be guarded by rcu_read_lock().
  97  */
  98 static inline void hlist_bl_add_head_rcu(struct hlist_bl_node *n,
  99                                         struct hlist_bl_head *h)
 100 {
 101         struct hlist_bl_node *first;
 102
 103         /* don't need hlist_bl_first_rcu because we're under lock */
 104         first = hlist_bl_first(h);
 105
 106         n->next = first;
 107         if (first)
 108                 first->pprev = &n->next;
 109         n->pprev = &h->first;
 110
 111         /* need _rcu because we can have concurrent lock free readers */
 112         hlist_bl_set_first_rcu(h, n);
 113 }
 114 /**
 115  * hlist_bl_for_each_entry_rcu - iterate over rcu list of given type
 116  * @tpos:       the type * to use as a loop cursor.
 117  * @pos:        the &struct hlist_bl_node to use as a loop cursor.
 118  * @head:       the head for your list.
 119  * @member:     the name of the hlist_bl_node within the struct.
 120  *
 121  */
 122 #define hlist_bl_for_each_entry_rcu(tpos, pos, head, member)            \
 123         for (pos = hlist_bl_first_rcu(head);                            \
 124                 pos &&                                                  \
 125                 ({ tpos = hlist_bl_entry(pos, typeof(*tpos), member); 1; }); \
 126                 pos = rcu_dereference_raw(pos->next))
 127
 128 #endif