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Date:	Thu, 3 Oct 2013 12:39:46 -0500
From:	Shawn Bohrer <sbohrer@...advisors.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>, tomk@...advisors.com,
	netdev <netdev@...r.kernel.org>
Subject: Re: [net-next 2/3] udp: Add udp early demux

On Wed, Oct 02, 2013 at 02:38:52PM -0700, Eric Dumazet wrote:
> I suggested that for unicast, you do a limited lookup to the first
> socket found in bucket.
> 
> If its an exact match, you take the socket.
> 
> If not, you give up, and do not scan the whole chain.

So something like the following?


diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 02185a5..d202e5b 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1849,7 +1849,42 @@ begin:
 	}
 	rcu_read_unlock();
 	return result;
+}
 
+/* For unicast we should only early demux connected sockets or we can
+ * break forwarding setups.  The chains here can be long so only check
+ * if the first socket is an exact match and if not move on.
+ */
+static struct sock *__udp4_lib_demux_lookup(struct net *net,
+					    __be16 loc_port, __be32 loc_addr,
+					    __be16 rmt_port, __be32 rmt_addr,
+					    int dif)
+{
+	struct sock *sk, *result;
+	struct hlist_nulls_node *node;
+	unsigned short hnum = ntohs(loc_port);
+	unsigned int slot = udp_hashfn(net, hnum, udp_table.mask);
+	struct udp_hslot *hslot = &udp_table.hash[slot];
+	const int exact_match = 18;
+	int score;
+
+	rcu_read_lock();
+	result = NULL;
+	sk_nulls_for_each_rcu(sk, node, &hslot->head) {
+		score = compute_score(sk, net, rmt_addr, hnum, rmt_port,
+				      loc_addr, loc_port, dif);
+		if (score == exact_match)
+			result = sk;
+		/* Only check first socket in chain */
+		break;
+	}
+
+	if (result) {
+		if (unlikely(!atomic_inc_not_zero_hint(&result->sk_refcnt, 2)))
+			result = NULL;
+	}
+	rcu_read_unlock();
+	return result;
 }
 
 void udp_v4_early_demux(struct sk_buff *skb)
@@ -1870,8 +1905,8 @@ void udp_v4_early_demux(struct sk_buff *skb)
 		sk = __udp4_lib_mcast_demux_lookup(net, uh->dest, iph->daddr,
 						   uh->source, iph->saddr, dif);
 	else if (skb->pkt_type == PACKET_HOST)
-		sk = __udp4_lib_lookup(net, iph->saddr, uh->source,
-				       iph->daddr, uh->dest, dif, &udp_table);
+		sk = __udp4_lib_demux_lookup(net, uh->dest, iph->daddr,
+					     uh->source, iph->saddr, dif);
 	else
 		return;
 

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