linux-kernel - Re: [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received

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Message-ID: <7d36a817-5519-8496-17cf-00eda5ed4ec7@gmail.com>
Date:   Fri, 31 Jan 2020 14:53:43 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Neal Cardwell <ncardwell@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     sjpark@...zon.com, Eric Dumazet <edumazet@...gle.com>,
        David Miller <davem@...emloft.net>, shuah@...nel.org,
        Netdev <netdev@...r.kernel.org>, linux-kselftest@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, sj38.park@...il.com,
        aams@...zon.com, SeongJae Park <sjpark@...zon.de>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is
 received



On 1/31/20 2:11 PM, Neal Cardwell wrote:

> I looked into fixing this, but my quick reading of the Linux
> tcp_rcv_state_process() code is that it should behave correctly and
> that a connection in FIN_WAIT_1 that receives a FIN/ACK should move to
> TIME_WAIT.
> 
> SeongJae, do you happen to have a tcpdump trace of the problematic
> sequence where the "process A" ends up in FIN_WAIT_2 when it should be
> in TIME_WAIT?
> 
> If I have time I will try to construct a packetdrill case to verify
> the behavior in this case.

Unfortunately you wont be able to reproduce the issue with packetdrill,
since it involved packets being processed at the same time (race window)