linux-kernel - Re: possible BUG: unable to handle kernel NULL pointer dereference at virtual address 00000000

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Message-ID: <20071201121220.GA28875@cvg>
Date:	Sat, 1 Dec 2007 15:12:20 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Udo van den Heuvel <udovdh@...all.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: possible BUG: unable to handle kernel NULL pointer dereference
	at virtual address 00000000

[Udo van den Heuvel - Sat, Dec 01, 2007 at 12:00:53PM +0100]
| Hallo Cyrill,
| 
| Cyrill Gorcunov wrote:
| > | I made a do while loop doing make bzImage modules and a make clean.
| > | Should be OK?
| > | 
| > 
| > well, test the patch enveloped. if the bug is really heppens then
| > BUG message should appear. and the thing is much important - does
| > that bug appears on the same actions (make bzImage and etc..) on pure
| > kernel? or that happened from time to time?
| 
| I only had teh bug once, that was the reason for my post.
| Since then the system has been busy, with intervals, doing kernel
| compiles and no repeat of the BUG yet...
| It's a VIA EN12000 with 1GB of RAM. How could I increase the chances of
| hitting it?
| 
| 
| Kind regards,
| Udo
|

Hi Udo,

if my guessing is right - the only chance to hit it faster - is to increase
files' activity i.e. compiling the kernel involves a lot of file being readed
thru dcache system. First we have to locate the bug on a pure kernel
and 'case it's a rare thing to happen... well I don't really know how to
get it up to known point. So i think you could play with a pure kernel
by compiling it or run several copies of 'grep' thru kernel searching
the same pattern like "grep -r -n for ./*" in kernel sources. But Udo,
I'm not a kernel specialist so my suggestions could be not really usefull ;)

And as only you have found "approximated events" when the bug happend -
then we could try the same actions with my latest patch applied to find
if it happening exactly in dcache system. (damn, so many *if* there ;)

if you will not find that bug being reproducible in a simple way - just
leave all as it is, i'm trying to find problems in dcache system by code
reading.

P.S.
Lets CC LKML - that could help us ;)

		Cyrill

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