linux-kernel - Re: PATCH/RFC: [kdump] fix APIC shutdown sequence

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Date:	Wed, 08 Aug 2007 11:03:17 +0200
From:	Martin Wilck <martin.wilck@...itsu-siemens.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"vgoyal@...ibm.com" <vgoyal@...ibm.com>,
	Haren Myneni <hbabu@...ibm.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: PATCH/RFC: [kdump] fix APIC shutdown sequence

Hello Eric,

> How bad is it if you just run with irqpoll in the kdump kernel?
> If running with irqpoll is usable that is probably preferable
> to putting in a hardware work around we can survive without.

Yes, I tried that. No effect.

> Have you done any looking at moving where the kernel initalizes
> io_apics?  One of the todo items on the path is to leave
> io_apic mode enabled and just startup the kernel in io_apic
> mode.

I have tried to recover from the "IRR set" situation in several ways by
changing setup_IO_APIC_irq(). But I haven't found a way to recover from
this situation once disable_IO_APIC() had been called.
I concluded thatthe sequence of events
"send INT message - never receive EOI - disable IO-APIC pin"
messes up the IO-APIC (at least this specific one in the
PCIEx-PCI bridge of the ICH7).

The current state of affairs is that the only thing that "worked" was to
re-enable irqs.

> When doing that a version of your work around (if needed)
> would certainly be reasonable.

> My general concern is that the trickier we get in the code
> running in the crashed kernel the less reliable the entire
> process will be.

That's certainly correct. I am grateful for all hints that simplify my patch.

Thanks,
Martin

-- 
Martin Wilck
PRIMERGY System Software Engineer
FSC IP ESP DE6

Fujitsu Siemens Computers GmbH
Heinz-Nixdorf-Ring 1
33106 Paderborn
Germany

Tel:			++49 5251 8 15113
Fax:			++49 5251 8 20409
Email:			mailto:martin.wilck@...itsu-siemens.com
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