Messages in this thread | | | Date | Mon, 22 Sep 2008 13:58:09 -0400 | From | Aristeu Rozanski <> | Subject | Re: [PATCH] NMI watchdog: when booting with reset_devices, clear the performance counters |
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> > 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@redhat.com> > > Acked-by: Don Zickus <dzickus@redhat.com> > > Acked-by: Prarit Bhargava <prarit@redhat.com> > > Acked-by: Vivek Goyal <vgoyal@redhat.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.
-- Aristeu
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