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Subject: Re: 2.6.21.5 june 30th to july 1st date hang?
From: Thomas Gleixner <tglx@linutronix.de>
To: Ernie Petrides <petrides@redhat.com>
Cc: Chris Friesen <cfriesen@nortel.com>,
       Clemens Koller <clemens.koller@anagramm.de>,
       Chris Wright <chrisw@sous-sol.org>, Uli Luckas <u.luckas@road.de>,
       LKML <linux-kernel@vger.kernel.org>
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References: <200707052312.l65NCjfb025915@pasta.boston.redhat.com>
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Date: Fri, 06 Jul 2007 07:17:26 +0200
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On Thu, 2007-07-05 at 19:12 -0400, Ernie Petrides wrote:
> On Thursday, 5-Jul-2007 at 16:49 MDT, Chris Friesen wrote:
> 
> > Ernie Petrides wrote:
> > 
> > > Only kernels built with the CONFIG_HIGH_RES_TIMERS option enabled were
> > > vulnerable.
> > 
> > As I mentioned in my post to Thomas, we have high res timers disabled 
> > and were still affected.  Granted, our kernel has been modified so it is 
> > possible that vanilla would not be affected....I haven't tested it.
> > 
> > Chris
> 
> That's odd, because Thomas's patch removed two calls to clock_was_set(),
> which is a no-op when CONFIG_HIGH_RES_TIMERS is not enabled (at least in
> the 2.6.21 source tree).
> 
> Also, I personally tested with the reproducer you posted here, initially
> on a box running 2.6.22-rc4, and there were no problems (but I'm not sure
> what config options were enabled on that kernel).  I did reproduce the
> problem on a stock 2.6.21 kernel with CONFIG_HIGH_RES_TIMERS enabled.

It needs a running smp_call_function() to be interrupted by the timer
interrupt, which calls clock_was_set(). So it's not that easy to
reproduce.

	tglx