linux-kernel - Re: Soft-Lockup/Race in networking in 2.6.31-rc1+195 ( possibly?caused by netem)

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Message-ID: <20090704063646.GA3410@ami.dom.local>
Date:	Sat, 4 Jul 2009 08:36:46 +0200
From:	Jarek Poplawski <jarkao2@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	andres@...razel.de, arun@...ux.vnet.ibm.com, tglx@...utronix.de,
	shemminger@...tta.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: Soft-Lockup/Race in networking in 2.6.31-rc1+195 (
	possibly?caused by netem)

On Fri, Jul 03, 2009 at 06:55:53PM -0700, David Miller wrote:
> From: Jarek Poplawski <jarkao2@...il.com>
> Date: Sat, 4 Jul 2009 00:56:40 +0200
> 
> > On Fri, Jul 03, 2009 at 01:22:20PM -0700, David Miller wrote:
> >> Well, if you look at that commit the bisect pointed to Jarek, it is a
> >> change which starts causing a situation which never happened before.
> >> Namely, timers added on one cpu can be migrated and fire on another.
> >> 
> >> So this could be exposing races in the networking that technically
> >> always existed.
> > 
> > I'm not sure I get your point; could you give some example?
> > Actually, I've suspected races in timers code.
> 
> Let's say that a particular networking timer always gets
> re-added on the cpu where the timer fires.
> 
> In that case, beforehand, no inter-cpu races could possibly
> be tested.  But with the new timer code, such races could
> now be potentially triggered.

Maybe I still miss something, but even if it were possible, lockdep
should have reported such things long ago.

Jarek P.
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