linux-kernel - Re: v2.6.26-rc7: BUG: unable to handle kernel NULL pointer dereference

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Date:	Thu, 26 Jun 2008 15:59:23 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Jason Wessel" <jason.wessel@...driver.com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	"Ingo Molnar" <mingo@...e.hu>, "Mike Travis" <travis@....com>,
	"Adrian Bunk" <bunk@...nel.org>,
	"Srivatsa Vaddagiri" <vatsa@...ibm.com>,
	linux-kernel@...r.kernel.org, "Gautham R Shenoy" <ego@...ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Zhang, Yanmin" <yanmin.zhang@...el.com>,
	"Heiko Carstens" <heiko.carstens@...ibm.com>,
	"Rusty Russell" <rusty@...tcorp.com.au>
Subject: Re: v2.6.26-rc7: BUG: unable to handle kernel NULL pointer dereference

On Thu, Jun 26, 2008 at 2:40 PM, Jason Wessel
<jason.wessel@...driver.com> wrote:
>> 4. Page fault in I'm guessing configure_kgdbts() during boot. Never
>> seen this before either (screenshot #2).
>>
>
> How often does #4 occur?

Only this once yet.

>
> Perhaps you can email me directly the .config and kernel boot arguments
> you used?  It would be good to determine if the #4 is a victim or
> culprit of the crash.  If it is a culprit I would like to try and fix it.

I don't think this really has anything to do with the CPU hotplug
crashing. It seems to be completely spurious, as this was during boot
before userspace had even started. It's not even certain that it has
anything to do with kgdb at all. I mean, that stack trace is not very
reliable...

Command line was: kernel /vmlinuz-2.6.26-rc8-dirty ro
root=/dev/VolGroup00/LogVol00 rhgb debug 3

You can find vmlinux and config here:

http://www.kernel.org/pub/linux/kernel/people/vegard/kernels/20080626/

..but it probably takes a bit for the mirrors to pick up. In the
meantime, I can provide you with the relevant line numbers:

# configure_kgdbts
$ addr2line -e vmlinux.20080626 -i c030ab18 | sed 's/.*linux-2.6\///'
drivers/misc/kgdbts.c:911
drivers/misc/kgdbts.c:1015

# mtrr_del
$ addr2line -e vmlinux.20080626 -i c011007b | sed 's/.*linux-2.6\///'
arch/x86/kernel/cpu/mtrr/main.c:548

# loop_init
$ addr2line -e vmlinux.20080626 -i c078111a | sed 's/.*linux-2.6\///'
drivers/block/loop.c:1550

# init_kgdbts
$ addr2line -e vmlinux.20080626 -i c0781163 | sed 's/.*linux-2.6\///'
drivers/misc/kgdbts.c:1033

Thanks.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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