netdev - Re: TCP sender stuck in persist despite peer advertising non-zero window

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Message-ID: <CADVnQym2cJGRP8JnRAdzHfWEeEbZrmXd3eXD-nFP6pRNK7beWw@mail.gmail.com>
Date:   Thu, 15 Oct 2020 18:37:37 -0400
From:   Neal Cardwell <ncardwell@...gle.com>
To:     Apollon Oikonomopoulos <apoikos@...sg.gr>
Cc:     Yuchung Cheng <ycheng@...gle.com>, Netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Soheil Hassas Yeganeh <soheil@...gle.com>
Subject: Re: TCP sender stuck in persist despite peer advertising non-zero window

On Thu, Oct 15, 2020 at 6:12 PM Apollon Oikonomopoulos <apoikos@...sg.gr> wrote:
>
> Yuchung Cheng <ycheng@...gle.com> writes:
>
> > On Thu, Oct 15, 2020 at 1:22 PM Neal Cardwell <ncardwell@...gle.com> wrote:
> >>
> >> On Thu, Oct 15, 2020 at 2:31 PM Apollon Oikonomopoulos <apoikos@...sg.gr> wrote:
> >> >
> >> > Hi,
> >> >
> >> > I'm trying to debug a (possible) TCP issue we have been encountering
> >> > sporadically during the past couple of years. Currently we're running
> >> > 4.9.144, but we've been observing this since at least 3.16.
> >> >
> >> > Tl;DR: I believe we are seeing a case where snd_wl1 fails to be properly
> >> > updated, leading to inability to recover from a TCP persist state and
> >> > would appreciate some help debugging this.
> >>
> >> Thanks for the detailed report and diagnosis. I think we may need a
> >> fix something like the following patch below.
>
> That was fast, thank you!
>
> >>
> >> Eric/Yuchung/Soheil, what do you think?
> > wow hard to believe how old this bug can be. The patch looks good but
> > can Apollon verify this patch fix the issue?
>
> Sure, I can give it a try and let the systems do their thing for a couple of
> days, which should be enough to see if it's fixed.

Great, thanks!

> Neal, would it be possible to re-send the patch as an attachment? The
> inlined version does not apply cleanly due to linewrapping and
> whitespace changes and, although I can re-type it, I would prefer to test
> the exact same thing that would be merged.

Sure, I have attached the "git format-patch" format of the commit. It
does seem to apply cleanly to the v4.9.144 kernel you mentioned you
are using.

Thanks for testing this!

best,
neal

Download attachment "0001-tcp-fix-to-update-snd_wl1-in-bulk-receiver-fast-path.patch" of type "application/x-patch" (1363 bytes)