From: Daniel Lezcano <dlezcano@fr.ibm.com>

Denis Lunev spotted that if we take a reference to the network namespace
with the timewait sockets, we will need to wait for their expiration to
have the network namespace freed. This is a waste of time, the timewait
sockets are for avoiding to receive a duplicate packet from the network,
if the network namespace is freed, the network stack is removed, so no
chance to receive any packets from the outside world.

This patchset remove/destroy the timewait sockets when the
network namespace is freed.

Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>
---
 net/ipv4/tcp.c |   53 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

Index: linux-2.6-netns/net/ipv4/tcp.c
===================================================================
--- linux-2.6-netns.orig/net/ipv4/tcp.c
+++ linux-2.6-netns/net/ipv4/tcp.c
@@ -2432,8 +2432,61 @@ static int tcp_net_init(struct net *net)
 	return 0;
 }
 
+/*
+ * Wipeout tcp timewait sockets, they are no longer needed
+ * because we destroy the network namespace, so no risk to
+ * have duplicate packet coming from the network
+ */
+static void tcp_net_exit(struct net *net)
+{
+	struct inet_timewait_sock *tw;
+	struct sock *sk;
+	struct hlist_node *node, *tmp;
+	int h;
+	int nbsock = 0;
+
+	/* Browse the the established hash table */
+	for (h = 0; h < (tcp_hashinfo.ehash_size); h++) {
+                struct inet_ehash_bucket *head =
+                        inet_ehash_bucket(&tcp_hashinfo, h);
+
+		/* Take the look and disable bh */
+ 		write_lock_bh(&head->lock);
+
+		sk_for_each_safe(sk, node, tmp, &head->twchain) {
+
+			tw = inet_twsk(sk);
+			if (tw->tw_net != net)
+				continue;
+
+			/* deschedule the timewait socket */
+			spin_lock(&tcp_death_row.death_lock);
+			if (inet_twsk_del_dead_node(tw)) {
+				inet_twsk_put(tw);
+				if (--tcp_death_row.tw_count == 0)
+					del_timer(&tcp_death_row.tw_timer);
+			}
+			spin_unlock(&tcp_death_row.death_lock);
+
+			/* remove it from the established hash table */
+			__inet_twsk_unehash(tw);
+
+			/* remove it from the bind hash table */
+			inet_twsk_unbhash(tw, tcp_death_row.hashinfo);
+
+			/* last put */
+			inet_twsk_put(tw);
+
+			nbsock++;
+		}
+
+		write_unlock_bh(&head->lock);
+	}
+}
+
 static struct pernet_operations tcp_net_ops = {
 	.init = tcp_net_init,
+	.exit = tcp_net_exit,
 };
 
 void __init tcp_init(void)

-- 
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