PATCH/RFC: [kdump] fix APIC shutdown sequence

Chip Coldwell coldwell at
Wed Aug 8 10:06:13 EDT 2007

On Wed, 8 Aug 2007, Vivek Goyal wrote:

> On Tue, Aug 07, 2007 at 07:41:30PM +0200, Martin Wilck wrote:
> > 
> > Can you explain how, on the front side bus, the IO-APIC knows whether
> > a CPU has accepted the INT message? There is no response
> > to the INT message on the bus, except for the EOI which comes much later.
> > I'm not saying that you're wrong, I just really don't understand this
> > point.
> > 
> I don't know what is exactly hardware protocol. I am just going by 
> intel documentation. 

I think it's important to distinguish between the LAPIC receiving an
interrupt and the CPU receiving an interrupt.  The former could happen
without the latter if the CPU has set the TPR above the priority of
the interrupt received by the LAPIC.  In that case, the interrupt is
kept pending in the LAPIC and recorded in the IRR if I understand the
Intel documentation correctly.

So I think the scenario which leaves IRR set when the kdump kernel
starts is possible.


Charles M. "Chip" Coldwell
Senior Software Engineer
Red Hat, Inc

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