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

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Date:   Thu, 22 Oct 2020 10:39:51 -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 22, 2020 at 8:47 AM Apollon Oikonomopoulos <apoikos@...sg.gr> wrote:
>
> Apollon Oikonomopoulos <apoikos@...sg.gr> writes:
> > We are now running the patched kernel on the machines involved. I want
> > to give it some time just to be sure, so I'll get back to you by
> > Thursday if everything goes well.
>
> It has been almost a week and we have had zero hangs in 60 rsync runs,
> so I guess we can call it fixed. At the same time we didn't notice any
> ill side-effects. In the unlikely event it hangs again, I will let you
> know.

Great. Many thanks for your testing and thorough analysis!

I agree that it's a little surprising that this bug would be there for
so long (looks like since Linux v2.1.8 in Nov 1996), but I also agree
with your analysis about why this might be so.

I have posted the proposed patch here:

  https://patchwork.ozlabs.org/project/netdev/patch/20201022143331.1887495-1-ncardwell.kernel@gmail.com/

best,
neal