net: udp_unhash() can test if sk is hashed

Impact: Optimization

Like done in inet_unhash(), we can avoid taking a chain lock if
socket is not hashed in udp_unhash()

Triggered by close(socket(AF_INET, SOCK_DGRAM, 0));
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -970,6 +970,7 @@ int udp_disconnect(struct sock *sk, int flags)
 
 void udp_lib_unhash(struct sock *sk)
 {
+	if (sk_hashed(sk)) {
 		struct udp_table *udptable = sk->sk_prot->h.udp_table;
 		unsigned int hash = udp_hashfn(sock_net(sk), sk->sk_hash);
 		struct udp_hslot *hslot = &udptable->hash[hash];
@@ -980,6 +981,7 @@ void udp_lib_unhash(struct sock *sk)
 			sock_prot_inuse_add(sock_net(sk), sk->sk_prot, -1);
 		}
 		spin_unlock_bh(&hslot->lock);
+	}
 }
 EXPORT_SYMBOL(udp_lib_unhash);