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

From: Stephen Hemminger <[email-masked]>
Date: Tue, 9 Mar 2010 08:22:03 -0800

On Tue, 09 Mar 2010 16:55:56 +0100
Eric Dumazet <[email-masked]> wrote:

> 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 <[email-masked]>
> Signed-off-by: Eric Dumazet <[email-masked]>
> ---
> 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);
> 
> 

Agreed.
Acked-by: Stephen Hemminger <[email-masked]>

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