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

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Date:	Thu, 26 Jun 2008 11:00:10 +0200
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Andrew Morton" <akpm@...ux-foundation.org>
Cc:	"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 4:15 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> Could.  But arch/x86/kernel/smpboot.c is an x86-tree file.  I'd expect
> the x86 maintainers would like a usable changelog and a Tested-by: (if
> indeed Vegard tested it).

Hi,

I had the patch (on top of v2.6.26-rc8) in testing for a couple of
hours now, but like I expected, the APIC error is really hard to
reproduce. So I fear that we never hit the failure case in the first
place. On the other hand... I hit a number of (other?) problems:

1. Spontaneous reboot. This could have been the APIC error thing, I
have no way to know. I've never seen this before.
2. NULL pointer dereference in pick_next_task_fair(). Not new.
3. NULL pointer dereference in page_cgroup_zoneinfo. Never seen this
before (see screenshot #1).
4. Page fault in I'm guessing configure_kgdbts() during boot. Never
seen this before either (screenshot #2).

So even though I'm inclined to believe the patch is correct, I will
not ack it or claim successful test coverage.

The screenshots:

#1: http://www.kernel.org/pub/linux/kernel/people/vegard/kernels/20080626/DSCF3017.JPG
#2: http://www.kernel.org/pub/linux/kernel/people/vegard/kernels/20080626/DSCF3018.JPG

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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