linux-kernel - Re: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in crash path

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Date:	Thu, 16 Feb 2012 16:56:03 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	torvalds@...ux-foundation.org, kexec@...ts.infradead.org,
	vgoyal@...hat.com, akpm@...ux-foundation.org, tglx@...utronix.de,
	mingo@...e.hu, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/debug] x86/kdump: No need to disable ioapic/ lapic in
 crash path

On Thu, Feb 16, 2012 at 01:53:29PM -0800, Yinghai Lu wrote:
> On Thu, Feb 16, 2012 at 9:27 AM, Don Zickus <dzickus@...hat.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.

Cool.  Thanks.

Eric,

Just let me know how you want to handle disabling NMIs in the kexec in
panic shutdown case.

Cheers,
Don
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