Messages in this thread | | | Date | Thu, 16 Feb 2012 12:27:35 -0500 | From | Don Zickus <> | Subject | 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@kernel.org> 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 *splat*.
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 disable_local_APIC?
Eric, thoughts, preferences?
Cheers, Don -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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