netdev - Re: IPv6 kernel warning

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Date:	Tue, 8 Oct 2013 10:56:54 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	dormando <dormando@...ia.net>,
	Michele Baldessari <michele@...syn.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	netdev <netdev@...r.kernel.org>,
	Nandita Dukkipati <nanditad@...gle.com>
Subject: Re: IPv6 kernel warning

On Tue, Oct 8, 2013 at 7:05 AM, Neal Cardwell <ncardwell@...gle.com> wrote:
> On Mon, Oct 7, 2013 at 3:51 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
>> I suspect tcp_process_tlp_ack() should not revert state to Open
>> directly, but calling tcp_try_keep_open() instead, similar to all the
>> undo processing in the tcp_fastretrans_alert(): after
>> tcp_end_cwnd_reduction(), the process (E) falls back to check other
>> stats before moving to CA_Open.
>>
>>
>> index 9c62257..9012b42 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -3314,7 +3314,7 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack,
>>                         tcp_init_cwnd_reduction(sk, true);
>>                         tcp_set_ca_state(sk, TCP_CA_CWR);
>>                         tcp_end_cwnd_reduction(sk);
>> -                       tcp_set_ca_state(sk, TCP_CA_Open);
>> +                       tcp_try_keep_open(sk);
>>                         NET_INC_STATS_BH(sock_net(sk),
>>                                          LINUX_MIB_TCPLOSSPROBERECOVERY);
>>                 }
>
> Yes, nice catch! This looks good to me. My testing confirms that this
> definitely fixes a bug when this code fires and there are segments
> SACKed out. Since it will stay in CA_Disorder if there are outstanding
> retransmissions, I bet it will also fix the WARN_ON(tp->retrans_out !=
> 0) in state TCP_CA_Open that people are seeing.
Sounds good. Let me do more tests then I will submit a bug fix.

>
> neal
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