tipc: tipc_udp_recv() cleanup vs rcu verbs

First thing tipc_udp_recv() does is to use rcu_dereference_sk_user_data(),
and this is really hinting we already own rcu_read_lock() from the caller
(UDP stack).

No need to add another rcu_read_lock()/rcu_read_unlock() pair.

Also use rcu_dereference() instead of rcu_dereference_rtnl()
in the data path.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jon Maloy <jon.maloy@ericsson.com>
Cc: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
index 6f166fb..7413cbc 100644
--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -354,10 +354,9 @@
 	skb_pull(skb, sizeof(struct udphdr));
 	hdr = buf_msg(skb);
 
-	rcu_read_lock();
-	b = rcu_dereference_rtnl(ub->bearer);
+	b = rcu_dereference(ub->bearer);
 	if (!b)
-		goto rcu_out;
+		goto out;
 
 	if (b && test_bit(0, &b->up)) {
 		tipc_rcv(sock_net(sk), skb, b);
@@ -368,11 +367,9 @@
 	if (unlikely(msg_user(hdr) == LINK_CONFIG)) {
 		err = tipc_udp_rcast_disc(b, skb);
 		if (err)
-			goto rcu_out;
+			goto out;
 	}
 
-rcu_out:
-	rcu_read_unlock();
 out:
 	kfree_skb(skb);
 	return 0;