ipv6: sctp: fix lockdep splat in sctp_v6_get_dst()

commit 69ce6487 upstream.

While cooking the sctp np->opt rcu fixes, I forgot to move
one rcu_read_unlock() after the added rcu_dereference() in
sctp_v6_get_dst()

This gave lockdep warnings reported by Dave Jones.

Fixes: c836a8ba ("ipv6: sctp: add rcu protection around np->opt")
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

net/sctp/ipv6.c

@@ -314,14 +314,13 @@ static void sctp_v6_get_dst(struct sctp_transport *t, union sctp_addr *saddr,
 			}
 		}
 	}
-	rcu_read_unlock();
-
 	if (baddr) {
 		ipv6_addr_copy(&fl6->saddr, &baddr->v6.sin6_addr);
 		fl6->fl6_sport = baddr->v6.sin6_port;
 		final_p = fl6_update_dst(fl6, np->opt, &final);
 		dst = ip6_dst_lookup_flow(sk, fl6, final_p, false);
 	}
+	rcu_read_unlock();
 
 out:
 	if (!IS_ERR(dst)) {