netdev - Re: tcp hang when socket fills up ?

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Message-ID: <20180417065252.yd4n62ydgqvd4hju@unicorn.suse.cz>
Date:   Tue, 17 Apr 2018 08:52:52 +0200
From:   Michal Kubecek <mkubecek@...e.cz>
To:     netdev@...r.kernel.org
Cc:     Florian Westphal <fw@...len.de>,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: tcp hang when socket fills up ?

On Mon, Apr 16, 2018 at 10:28:11PM -0700, Eric Dumazet wrote:
> > I turned pr_debug on in tcp_in_window() for another try and it's a bit
> > mangled because the information on multiple lines and the function is
> > called in parallel but it looks like I do have some seq > maxend +1
> > 
> > Although it's weird, the maxend was set WAY earlier apparently?
> > Apr 17 11:13:14 res=1 sender end=1913287798 maxend=1913316998 maxwin=29312 receiver end=505004284 maxend=505033596 maxwin=29200
> > then window decreased drastically e.g. previous ack just before refusal:
> > Apr 17 11:13:53 seq=1913292311 ack=505007789+(0) sack=505007789+(0) win=284 end=1913292311
> > Apr 17 11:13:53 sender end=1913292311 maxend=1913331607 maxwin=284 scale=0 receiver end=505020155 maxend=505033596 maxwin=39296 scale=7
> 
> scale=0 is suspect.
> 
> Really if conntrack does not see SYN SYNACK packets, it should not
> make any window check, since windows can be scaled up to 14 :/

Or maybe set the scaling to

  - TCP_MAX_WSCALE (14) by default
  - 0 when SYN or SYNACK without window scale option is seen
  - value of window scale option when SYN or SYNACK with it is seen

Michal Kubecek