tcp/dccp: fix possible race __inet_lookup_established()

[mirror_ubuntu-bionic-kernel.git] / include / linux / rculist_nulls.h

diff --git a/include/linux/rculist_nulls.h b/include/linux/rculist_nulls.h
index e4b257ff881bfe439a945d7487f5700f17a26740..a10da545b3f670c91caced56b85200f788403dd5 100644 (file)
--- a/include/linux/rculist_nulls.h
+++ b/include/linux/rculist_nulls.h
@@ -100,6 +100,43 @@ static inline void hlist_nulls_add_head_rcu(struct hlist_nulls_node *n,
                first->pprev = &n->next;
 }
 
+/**
+ * hlist_nulls_add_tail_rcu
+ * @n: the element to add to the hash list.
+ * @h: the list to add to.
+ *
+ * Description:
+ * Adds the specified element to the specified hlist_nulls,
+ * while permitting racing traversals.
+ *
+ * The caller must take whatever precautions are necessary
+ * (such as holding appropriate locks) to avoid racing
+ * with another list-mutation primitive, such as hlist_nulls_add_head_rcu()
+ * or hlist_nulls_del_rcu(), running on this same list.
+ * However, it is perfectly legal to run concurrently with
+ * the _rcu list-traversal primitives, such as
+ * hlist_nulls_for_each_entry_rcu(), used to prevent memory-consistency
+ * problems on Alpha CPUs.  Regardless of the type of CPU, the
+ * list-traversal primitive must be guarded by rcu_read_lock().
+ */
+static inline void hlist_nulls_add_tail_rcu(struct hlist_nulls_node *n,
+                                           struct hlist_nulls_head *h)
+{
+       struct hlist_nulls_node *i, *last = NULL;
+
+       /* Note: write side code, so rcu accessors are not needed. */
+       for (i = h->first; !is_a_nulls(i); i = i->next)
+               last = i;
+
+       if (last) {
+               n->next = last->next;
+               n->pprev = &last->next;
+               rcu_assign_pointer(hlist_next_rcu(last), n);
+       } else {
+               hlist_nulls_add_head_rcu(n, h);
+       }
+}
+
 /**
  * hlist_nulls_for_each_entry_rcu - iterate over rcu list of given type
  * @tpos:      the type * to use as a loop cursor.