netdev - Re: Linux 3.6.x kernel crash in tcp_slow_start / bictcp_cong

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Message-ID: <20130124135120.GD16641@order.stressinduktion.org>
Date:	Thu, 24 Jan 2013 14:51:20 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Stephen Hemminger <stephen@...workplumber.org>,
	Pasi Kärkkäinen <pasik@....fi>,
	netdev@...r.kernel.org
Subject: Re: Linux 3.6.x kernel crash in tcp_slow_start / bictcp_cong_avoid with wfica

On Wed, Jan 23, 2013 at 03:47:11PM -0800, Eric Dumazet wrote:
> On Thu, 2013-01-24 at 00:41 +0100, Hannes Frederic Sowa wrote:
> > On Wed, Jan 23, 2013 at 03:26:42PM -0800, Stephen Hemminger wrote:
> > > I see no problems when using Citrix.
> > > This is a normal strace of the program wifca (in idle loop)
> > 
> > Thanks, could you also have a look at setsockopts while socket creation and
> > connection establishment?
> 
> As I said, tp->snd_cwnd is set to 0 by a bug in TCP stack.

I saw this, too, but hoped to see a reproduceable pattern of setsockopts
(window clamping, switching of congestion control) that could make citrix in
some way the special application which causes this. 

> Probably a combination of changed sysctls, and a genuine bug.
> 
> Please give us /etc/sysctl.conf content.
> 
> Adding some BUG_ON(!tp->snd_cwnd) on every writes to tp->snd_cwnd should
> catch the bug.

But this is much more convenient, yes. :)

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