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

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Message-Id: <20090703.185553.218218176.davem@davemloft.net>
Date:	Fri, 03 Jul 2009 18:55:53 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	jarkao2@...il.com
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)

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.
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