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

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Date:   Fri, 31 Jan 2020 23:17:55 +0100
From:   SeongJae Park <sj38.park@...il.com>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>, 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: Re: [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received

On Fri, 31 Jan 2020 17:11:35 -0500 Neal Cardwell <ncardwell@...gle.com> wrote:

> On Fri, Jan 31, 2020 at 1:12 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
> >
> >
> >
> > On 1/31/20 7:10 AM, Neal Cardwell wrote:
> > > On Fri, Jan 31, 2020 at 7:25 AM <sjpark@...zon.com> wrote:
> > >>
> > >> From: SeongJae Park <sjpark@...zon.de>
> > >>
> > >> When closing a connection, the two acks that required to change closing
> > >> socket's status to FIN_WAIT_2 and then TIME_WAIT could be processed in
> > >> reverse order.  This is possible in RSS disabled environments such as a
> > >> connection inside a host.
[...]
> 
> 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?

Hi Neal,


Yes, I have.  You can get it from the previous discussion for this patchset
(https://lore.kernel.org/bpf/20200129171403.3926-1-sjpark@amazon.com/).  As it
also has a reproducer program and how I got the tcpdump trace, I believe you
could get your own trace, too.  If you have any question or need help, feel
free to let me know. :)


Thanks,
SeongJae Park

> 
> If I have time I will try to construct a packetdrill case to verify
> the behavior in this case.
> 
> thanks,
> neal
> 
> >