ipv6: refactor ip6_finish_output2()

Throw neigh checks in ip6_finish_output2() under a single slow path if,
so we don't have the overhead in the hot path.
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/ip6_output.c

@@ -119,19 +119,21 @@ static int ip6_finish_output2(struct net *net, struct sock *sk, struct sk_buff *
 	rcu_read_lock_bh();
 	nexthop = rt6_nexthop((struct rt6_info *)dst, daddr);
 	neigh = __ipv6_neigh_lookup_noref(dev, nexthop);
-	if (unlikely(!neigh))
-		neigh = __neigh_create(&nd_tbl, nexthop, dev, false);
-	if (!IS_ERR(neigh)) {
-		sock_confirm_neigh(skb, neigh);
-		ret = neigh_output(neigh, skb, false);
-		rcu_read_unlock_bh();
-		return ret;
+
+	if (unlikely(IS_ERR_OR_NULL(neigh))) {
+		if (unlikely(!neigh))
+			neigh = __neigh_create(&nd_tbl, nexthop, dev, false);
+		if (IS_ERR(neigh)) {
+			rcu_read_unlock_bh();
+			IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTNOROUTES);
+			kfree_skb_reason(skb, SKB_DROP_REASON_NEIGH_CREATEFAIL);
+			return -EINVAL;
+		}
 	}
+	sock_confirm_neigh(skb, neigh);
+	ret = neigh_output(neigh, skb, false);
 	rcu_read_unlock_bh();
-
-	IP6_INC_STATS(net, idev, IPSTATS_MIB_OUTNOROUTES);
-	kfree_skb_reason(skb, SKB_DROP_REASON_NEIGH_CREATEFAIL);
-	return -EINVAL;
+	return ret;
 }
 
 static int