linux-kernel - Re: [PATCH] NMI watchdog: when booting with reset

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Message-ID: <20080922175924.GH10535@elte.hu>
Date:	Mon, 22 Sep 2008 19:59:24 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Aristeu Rozanski <aris@...hat.com>
Cc:	linux-kernel@...r.kernel.org, dzickus@...hat.com,
	prarit@...hat.com, vgoyal@...hat.com
Subject: Re: [PATCH] NMI watchdog: when booting with reset_devices, clear
	the performance counters


* Aristeu Rozanski <aris@...hat.com> wrote:

> > > P4s have a quirk that makes necessary to clear P4_CCCR_OVF bit on the CCCR
> > > everytime the PMI is triggered. When booting the kernel with reset_devices
> > > (more specific kdump case), the counters reach zero and the PMI will be
> > > generated. This is not a problem on other processors but on P4s, it'll
> > > continue to generate NMIs until that bit is cleared. Since there may be
> > > other users of the performance counters, clear and disable all of them
> > > when booting with reset_devices option.
> > > 
> > > We have a P4 box here that crashes because of this problem. Since the kdump
> > > kernel usually boots with only one processor active, the second logical
> > > unit won't be set up, therefore, MSR_P4_IQ_CCCR1 (and other performance
> > > counter registers) won't be cleared and P4_CCCR_OVF may be still set because
> > > the previous kernel was using this register. An NMI is triggered because of
> > > the MSR_P4_IQ_CCCR1 right after the NMI delivery is enabled, triggering the
> > > race fixed on my previous email.
> > > 
> > > Signed-off-by: Aristeu Rozanski <aris@...hat.com>
> > > Acked-by: Don Zickus <dzickus@...hat.com>
> > > Acked-by: Prarit Bhargava <prarit@...hat.com>
> > > Acked-by: Vivek Goyal <vgoyal@...hat.com>
> > 
> > applied to tip/x86/nmi-watchdog, thanks.
> > 
> > i'm wondering, is this fix a v2.6.27 candidate?
> I believe so. Even being a small affected group (P4 based boxes using NMI
> watchdog and kdump), it's fully reproducible.

is there a bugzilla.kernel.org entry for it? If not, could you please 
file it? Thanks,

	Ingo
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