netdev - Re: [PATCH] tcp: keepalive fixes

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Date:   Tue, 12 Jan 2021 23:52:43 +0100
From:   Eric Dumazet <edumazet@...gle.com>
To:     Yuchung Cheng <ycheng@...gle.com>
Cc:     Enke Chen <enkechen2020@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH] tcp: keepalive fixes

On Tue, Jan 12, 2021 at 11:48 PM Yuchung Cheng <ycheng@...gle.com> wrote:
>
> On Tue, Jan 12, 2021 at 2:31 PM Enke Chen <enkechen2020@...il.com> wrote:
> >
> > From: Enke Chen <enchen@...oaltonetworks.com>
> >
> > In this patch two issues with TCP keepalives are fixed:
> >
> > 1) TCP keepalive does not timeout when there are data waiting to be
> >    delivered and then the connection got broken. The TCP keepalive
> >    timeout is not evaluated in that condition.
> hi enke
> Do you have an example to demonstrate this issue -- in theory when
> there is data inflight, an RTO timer should be pending (which
> considers user-timeout setting). based on the user-timeout description
> (man tcp), the user timeout should abort the socket per the specified
> time after data commences. some data would help to understand the
> issue.
>

+1

A packetdrill test would be ideal.

Also, given that there is this ongoing issue with TCP_USER_TIMEOUT,
lets not mix things
or risk added work for backports to stable versions.