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Date: Wed, 08 Aug 2007 20:07:13 +0200
From: Martin Wilck <martin.wilck@...itsu-siemens.com>
To: "vgoyal@...ibm.com" <vgoyal@...ibm.com>
Cc: 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
Vivek Goyal wrote:
> Got this oops while testing your patch when I did
> "echo c > /proc/sysrq-trigger"
That's bad :-(
...
> Unable to handle kernel NULL pointer dereference at 0000000000000000 RIP:
[<0000000000000000>]
> <IRQ> [<ffffffff8025afd0>] handle_edge_irq+0x5c/0x127
> [<ffffffff8020e1ae>] do_IRQ+0xf1/0x15f
> [<ffffffff8020c191>] ret_from_intr+0x0/0xa
> <EOI> <NMI> [<ffffffff80351ae3>] __delay+0x6/0x10
> [<ffffffff8021e328>] crash_nmi_callback+0x4b/0x77
Obviously, it the oops occurs after the IRQs are re-enabled in crash_nmi_callback().
It appears that desc->chip->mask (in mask_ack_irq(), kernel/irq/chip.c:462) was NULL.
I have no idea how my patch could cause that.
This proves that re-enabling IRQs in this situation is too dangerous :-(.
I really did hundreds of dumps in different ways (echo c>/proc/sysrq-trigger,
forcing Oops and panic(), actually hititng Alt-Sysrq) and this never happened to
me.
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
Internet: http://www.fujitsu-siemens.com
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