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From: Neal Cardwell <ncardwell@google.com>
To: SeongJae Park <sj38.park@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	sjpark@amazon.com, Eric Dumazet <edumazet@google.com>,
	David Miller <davem@davemloft.net>,
	shuah@kernel.org, Netdev <netdev@vger.kernel.org>,
	linux-kselftest@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>,
	aams@amazon.com, SeongJae Park <sjpark@amazon.de>,
	Yuchung Cheng <ycheng@google.com>
Subject: Re: Re: [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received
Date: Fri, 31 Jan 2020 22:55:34 -0500	[thread overview]
Message-ID: <CADVnQy=oFmmG-Z9QMafWLcALOBgohADgwScn2r+7CGFNAw5jvw@mail.gmail.com> (raw)
In-Reply-To: <20200131221755.3874-1-sj38.park@gmail.com>

On Fri, Jan 31, 2020 at 5:18 PM SeongJae Park <sj38.park@gmail.com> wrote:
>
> On Fri, 31 Jan 2020 17:11:35 -0500 Neal Cardwell <ncardwell@google.com> wrote:
>
> > On Fri, Jan 31, 2020 at 1:12 PM Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > >
> > >
> > >
> > > On 1/31/20 7:10 AM, Neal Cardwell wrote:
> > > > On Fri, Jan 31, 2020 at 7:25 AM <sjpark@amazon.com> wrote:
> > > >>
> > > >> From: SeongJae Park <sjpark@amazon.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. :)

Great. Thank you for the pointer.

I had one quick question: in the message:
  https://lore.kernel.org/bpf/20200129171403.3926-1-sjpark@amazon.com/
... it showed a trace with the client sending a RST/ACK, but this
email thread shows a FIN/ACK. I am curious about the motivation for
the difference?

Anyway, thanks for the report, and thanks to Eric for further clarifying!

neal

  reply	other threads:[~2020-02-01  3:55 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-31 12:24 [PATCH 0/3] Fix reconnection latency caused by FIN/ACK handling race sjpark
2020-01-31 12:24 ` [PATCH 1/3] net/ipv4/inet_timewait_sock: Fix inconsistent comments sjpark
2020-01-31 14:54   ` Eric Dumazet
2020-01-31 15:09     ` sjpark
2020-01-31 12:24 ` [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received sjpark
2020-01-31 15:01   ` Eric Dumazet
2020-01-31 16:12     ` sjpark
2020-01-31 16:55       ` Eric Dumazet
2020-01-31 17:05         ` sjpark
2020-01-31 17:08           ` Eric Dumazet
2020-01-31 15:10   ` Neal Cardwell
2020-01-31 18:12     ` Eric Dumazet
2020-01-31 22:11       ` Neal Cardwell
2020-01-31 22:17         ` SeongJae Park
2020-02-01  3:55           ` Neal Cardwell [this message]
2020-02-01  6:08             ` SeongJae Park
2020-02-01 13:30               ` Neal Cardwell
2020-01-31 22:53         ` Eric Dumazet
2020-02-03 15:40           ` David Laight
2020-02-03 15:54             ` Eric Dumazet
2020-01-31 12:24 ` [PATCH 3/3] selftests: net: Add FIN_ACK processing order related latency spike test sjpark
2020-01-31 14:56   ` Eric Dumazet
2020-01-31 15:13     ` sjpark
2020-01-31 14:00 ` [PATCH 0/3] Fix reconnection latency caused by FIN/ACK handling race David Laight
2020-01-31 15:05   ` sjpark

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