Re: [PATCH] x86, kdump, ioapic: Fix kdump race with migrating irq

From: Don Zickus
Date: Thu Feb 02 2012 - 10:33:29 EST

On Wed, Feb 01, 2012 at 05:34:01PM -0800, Eric W. Biederman wrote:
> > Talking to folks here and trying to read the code it seems like the PIT
> > stuff is delayed until after the IOAPIC is configured using Fast TSC
> > calibration as a mechanism to work around the PIT??
> >
> > I attached the output of the Pentium4 when kdumping. Not sure what to
> > really look for to verify the PIC is being skipped. Perhaps you know?
> The important part is the kexec on panic works without shutting down
> the ioapic. There should be no corner case issues it should either
> work it should fail.
> The problem used to be that we always would initialize the PIT interrupt
> in the 8259 interrupt controller before we would initialize the ioapics
> and that would kill the boot.
> If I have read your testing correctly you are apparently booting in the
> kexec on panic case. That seems to be successful to me. So we should
> be able to just remove the ioapic shutdown code from
> machine_crash_shutdown as it is no longer needed.
> Thank you for being careful and testing on a number of different
> platforms.

No problem. I was actually trying to find machines that did not have
ioapics to make sure they still worked (it's hard!).

So if I test on a couple more machines (hopefully one without an ioapic),
can I get your ack? Or is there something else you would like me to do to
verify things are working correctly?

I will also need your help writing the changelog such that people
understand why removing that line is safe now.

> The only case I can think that won't work without ioapic disables
> is using a crash kernel that doesn't emable the ioapics.

Ok. I can see that. Would you agree that scenario is not a very sane
case? :-) Does not using the ioapic really save you anything?

Otherwise the alternative is to use my original patch.

Thanks for the help.


> Eric
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