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

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On Mon, Feb 13, 2012 at 10:16:00AM -0800, Yinghai Lu wrote:
> On Mon, Feb 13, 2012 at 8:51 AM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> >> So I suspect we have a bug in our apic initialization somewhere, but
> >> apic initialization should happen after printk are enabled.  Or at least
> >> after early printks so the reset YH is reporting doesn't make much sense.
> >
> > will try Don's first version patch that only removing disable_IO_APIC.
> first version patch (only removing disable_IO_APIC) is working.

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

Yinghai, you can probably prove this by

echo 0 > /proc/sys/kernel/nmi_watchdog

then do your kdump crash test.

At least that test worked for me.

So either we explicitly shutdown perf or just mask off LVTPC in a modified

Eric, thoughts, preferences?

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