netdev - Re: [PATCH net] tcp: make TCP_USER_TIMEOUT accurate for zero window probes

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Date:   Sat, 23 Jan 2021 16:56:43 -0800
From:   Enke Chen <enkechen2020@...il.com>
To:     Neal Cardwell <ncardwell@...gle.com>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, enkechen2020@...il.com
Subject: Re: [PATCH net] tcp: make TCP_USER_TIMEOUT accurate for zero window
 probes

Hi, Neal:

What you described is more accurate, and is correct.

Thanks.  -- Enke

On Sat, Jan 23, 2021 at 07:19:13PM -0500, Neal Cardwell wrote:
> On Fri, Jan 22, 2021 at 9:45 PM Enke Chen <enkechen2020@...il.com> wrote:
> >
> > Hi, Jakub:
> >
> > On Fri, Jan 22, 2021 at 06:34:24PM -0800, Jakub Kicinski wrote:
> > > On Fri, 22 Jan 2021 18:28:23 -0800 Enke Chen wrote:
> > > > Hi, Jakub:
> > > >
> > > > In terms of backporting, this patch should go together with:
> > > >
> > > >     9d9b1ee0b2d1 tcp: fix TCP_USER_TIMEOUT with zero window
> > >
> > > As in it:
> > >
> > > Fixes: 9d9b1ee0b2d1 tcp: fix TCP_USER_TIMEOUT with zero window
> > >
> > > or does it further fix the same issue, so:
> > >
> > > Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT")
> > >
> > > ?
> >
> > Let me clarify:
> >
> > 1) 9d9b1ee0b2d1 tcp: fix TCP_USER_TIMEOUT with zero window
> >
> >    fixes the bug and makes it work.
> >
> > 2) The current patch makes the TCP_USER_TIMEOUT accurate for 0-window probes.
> >    It's independent.
> 
> Patch (2) ("tcp: make TCP_USER_TIMEOUT accurate for zero window
> probes") is indeed conceptually independent of (1) but its
> implementation depends on the icsk_probes_tstamp field defined in (1),
> so AFAICT (2) cannot be backported further back than (1).
> 
> Patch (1) fixes a bug in 5.1:
>     Fixes: 9721e709fa68 ("tcp: simplify window probe aborting on USER_TIMEOUT")
> 
> So probably (1) and (2) should be backported as a pair, and only back
> as far as 5.1. (That covers 2 LTS kernels, 5.4 and 5.10, so hopefully
> that is good enough.)
> 
> neal