On Oct 28, 2008, at 1:37 PM, Eric Dumazet wrote:

-extern struct hlist_head udp_hash[UDP_HTABLE_SIZE];
-extern rwlock_t udp_hash_lock;
+struct udp_hslot {
+	struct hlist_head	head;
+	rwlock_t		lock;
+};

This structure should be aligned up to cacheline to reduce false  
sharing of more than one hslot.

+	} else {
+		hslot = &udptable->hash[udp_hashfn(net, snum)];
+		write_lock_bh(&hslot->lock);
+		if (udp_lib_lport_inuse(net, snum, hslot, sk, saddr_comp))
+			goto fail;

The fail: label below should still unlock_bh when the above condition  
fails.

+	}
	inet_sk(sk)->num = snum;
	sk->sk_hash = snum;
	if (sk_unhashed(sk)) {
-		sk_add_node(sk, &udptable[udp_hashfn(net, snum)]);
+		sk_add_node(sk, &hslot->head);
		sock_prot_inuse_add(sock_net(sk), sk->sk_prot, 1);
	}
+	write_unlock_bh(&hslot->lock);
	error = 0;
fail:
-	write_unlock_bh(&udp_hash_lock);
	return error;
}

cheers,

	. . christian