ipv6: use RCU in inet6_csk_xmit()

Use RCU to avoid changing dst_entry refcount in fast path.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/inet6_connection_sock.c

@@ -211,6 +211,7 @@ int inet6_csk_xmit(struct sk_buff *skb, struct flowi *fl_unused)
 	struct flowi6 fl6;
 	struct dst_entry *dst;
 	struct in6_addr *final_p, final;
+	int res;
 
 	memset(&fl6, 0, sizeof(fl6));
 	fl6.flowi6_proto = sk->sk_protocol;
@@ -241,12 +242,14 @@ int inet6_csk_xmit(struct sk_buff *skb, struct flowi *fl_unused)
 		__inet6_csk_dst_store(sk, dst, NULL, NULL);
 	}
 
-	skb_dst_set(skb, dst_clone(dst));
+	rcu_read_lock();
+	skb_dst_set_noref(skb, dst);
 
 	/* Restore final destination back after routing done */
 	ipv6_addr_copy(&fl6.daddr, &np->daddr);
 
-	return ip6_xmit(sk, skb, &fl6, np->opt);
+	res = ip6_xmit(sk, skb, &fl6, np->opt);
+	rcu_read_unlock();
+	return res;
 }
-
 EXPORT_SYMBOL_GPL(inet6_csk_xmit);