linux-kernel - Re: WARNING: at net/ipv4/tcp_input.c:2927 tcp

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Date:	Mon, 30 Mar 2009 19:01:22 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Markus Trippelsdorf <markus@...ppelsdorf.de>
cc:	Netdev <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, corbet@....net
Subject: Re: WARNING: at net/ipv4/tcp_input.c:2927 tcp_ack+0xd55/0x1991()

On Sat, 28 Mar 2009, Markus Trippelsdorf wrote:

> On Sat, Mar 28, 2009 at 10:29:58AM +0200, Ilpo Järvinen wrote:
> > On Sat, 28 Mar 2009, Markus Trippelsdorf wrote:
> > 
> > > On Sat, Mar 28, 2009 at 01:05:09AM +0200, Ilpo Järvinen wrote:
> > > > On Fri, 27 Mar 2009, Markus Trippelsdorf wrote:
> > > > 
> > > > > I'm running the latest git kernel (2.6.29-03321-gbe0ea69) and I've got
> > > > > this warning twice in the last few hours.:

> > > > > The machine hangs afterwards.
> > > > 
> > > > Is it really related to the warning for sure? I find it hard to 
> > > > believe...
> > > 
> > > The machine is normally running stable for days. Switching back to 2.6.29
> > > solves the problem...
> > 
> > Sure, but does is hang right after printing that warning or much later on,
> > e.g., one minute is already a very long time for the crash to be related 
> > to that warning... Even 5 seconds is a long time but I'd immediately say 
> > it's not related then :-).
> 
> I really can't tell you. In both occurrences of the warning the machine
> was already unusable when I noticed. I then rebooted and the last entry
> in the logs was that warning.

...And, let me guess, you're in X and therefore unable to catch a final 
oops if any would be printed? It would be nice to get around that as well, 
either use serial/netconsole or hang in text mode while waiting for the 
crash (should be too hard if you are able to setup the workload first 
and then switch away from X and if reproducing takes about an hour)...

Arguably the presence of that warning at both times is somewhat alarming.

> > So you never saw this warning before within 2.6.29 or 2.6.28-26 timeframe?
> 
> Thats right.

And you were looking for them too at that time? If you still have old logs 
available you can verify that easily... if they're compressed you'll need 
something like this:
 for i in <logfiles*.gz>; do gunzip -c -d $i | grep "tcp_input"; done)

-- 
 i.