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Date: Thu, 16 Feb 2012 13:53:29 -0800
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Subject: Re: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in
 crash path
From: Yinghai Lu <yinghai@kernel.org>
To: Don Zickus <dzickus@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>, linux-kernel@vger.kernel.org,
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On Thu, Feb 16, 2012 at 9:27 AM, Don Zickus <dzickus@redhat.com> wrote:

> So I think I figured it out.  I went through and commented out code in
> disable_local_APIC until I narrowed it down to the piece of code that
> needs to be disabled for it to work.
>
> Surprise, surprise... its LVTPC or perf! :-)  Actually it is the
> nmi_watchdog which uses perf.  My theory is NMIs are not disabled and one
> is generated by the local apic during decompression (just bad timing) and
> *splat*.
>
> Yinghai, you can probably prove this by
>
> echo 0 > /proc/sys/kernel/nmi_watchdog
>
> then do your kdump crash test.

yes.  that will make kdump crash working.

Yinghai