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

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Date:	Wed, 08 Aug 2007 20:15:32 +0200
From:	Martin Wilck <martin.wilck@...itsu-siemens.com>
To:	"vgoyal@...ibm.com" <vgoyal@...ibm.com>
Cc:	Chip Coldwell <coldwell@...hat.com>,
	Haren Myneni <hbabu@...ibm.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: PATCH/RFC: [kdump] fix APIC shutdown sequence

Vivek Goyal wrote:

> But the issue here seems to be that LAPIC state got clear but IRR bit
> at IOAPIC bit is not cleared because IOAPIC vector information was deleted
> in first kernel and now upon receiving EOI, it does not know this EOI belongs
> to which vector.

I am making another experiment right now. I check the LAPIC ISR flags in
machine_crash_shutdown() before disabling the LAPIC, trying to send EOI if
I find one ISR bit set. So far, I haven't seen a single case where an ISR bit
was set, but several (9) where the IO-APIC IRR bit was set. OTOH, I know that if
I'd re-enable IRQs, IRQ 225 would be raised. The whole thing is done before
disable_IO_APIC().

Don't ask me for an explanation why I don't see the ISR bits.

The arch/x86_64/kernel/crash.c portion of the patch I am using is attached for
your reference. The rest is the same as for the original patch.

Martin

-- 
Martin Wilck
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FSC IP ESP DE6

Fujitsu Siemens Computers GmbH
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View attachment "kdump_23.diff" of type "text/x-patch" (3926 bytes)