netdev - Re: [2.6.34-rc1] CPU stalls when closing TCP sockets.

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Date:	Tue, 09 Mar 2010 16:55:56 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	paulmck@...ux.vnet.ibm.com,
	Stephen Hemminger <shemminger@...tta.com>
Subject: Re: [2.6.34-rc1] CPU stalls when closing TCP sockets.

Le mardi 09 mars 2010 à 15:54 +0900, Tetsuo Handa a écrit :
> Eric Dumazet wrote:
> > Nothing comes to my mind, I'll try to reproduce this here.
> 
> When stopped at (8), Ctrl-C doesn't work.
> 
> > Is 2.6.33 OK ?
> 
> Yes. 2.6.33 and earlier are OK.

OK thanks !

I believe commit d218d11133d888f9745802146a50255a4781d37a
(tcp: Generalized TTL Security Mechanism) might be the bug origin.

I am testing following patch, based on latest net-2.6 tree (including
the LINUX_MIB_TCPMINTTLDROP bit)

[PATCH] tcp: Fix tcp_v4_rcv()

Commit d218d111 (tcp: Generalized TTL Security Mechanism) added a bug
for TIMEWAIT sockets. We should not test min_ttl for TW sockets.

Reported-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
---
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 8d51d39..70df409 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1651,15 +1651,15 @@ int tcp_v4_rcv(struct sk_buff *skb)
 	if (!sk)
 		goto no_tcp_socket;
 
+process:
+	if (sk->sk_state == TCP_TIME_WAIT)
+		goto do_time_wait;
+
 	if (unlikely(iph->ttl < inet_sk(sk)->min_ttl)) {
 		NET_INC_STATS_BH(net, LINUX_MIB_TCPMINTTLDROP);
 		goto discard_and_relse;
 	}
 
-process:
-	if (sk->sk_state == TCP_TIME_WAIT)
-		goto do_time_wait;
-
 	if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
 		goto discard_and_relse;
 	nf_reset(skb);


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