linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference at 0000000000000500

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Message-ID: <50DCDEE5.9000700@iskon.hr>
Date:	Fri, 28 Dec 2012 00:51:01 +0100
From:	Zlatko Calusic <zlatko.calusic@...on.hr>
To:	sedat.dilek@...il.com
CC:	LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at 0000000000000500

On 28.12.2012 00:42, Sedat Dilek wrote:
> On Fri, Dec 28, 2012 at 12:39 AM, Zlatko Calusic
> <zlatko.calusic@...on.hr> wrote:
>> On 28.12.2012 00:30, Sedat Dilek wrote:
>>>
>>> Hi Zlatko,
>>>
>>> I am not sure if I hit the same problem as described in this thread.
>>>
>>> Under heavy load, while building a customized toolchain for the Freetz
>>> router project I got a BUG || NULL pointer derefence || kswapd ||
>>> zone_balanced || pgdat_balanced() etc. (details see my screenshot).
>>>
>>> I will try your patch from [1] ***only*** on top of my last
>>> Linux-v3.8-rc1 GIT setup (post-v3.8-rc1 mainline + some net-fixes).
>>>
>>
>> Yes, that's the same bug. It should be fixed with my latest patch, so I'd
>> appreciate you testing it, to be on the safe side this time. There should be
>> no difference if you apply it to anything newer than 3.8-rc1, so go for it.
>> Thanks!
>>
>
> Not sure how I can really reproduce this bug as one build worked fine
> within my last v3.8-rc1 kernel.
> I increased the parallel-make-jobs-number from "4" to "8" to stress a
> bit harder.
> Just building right now... and will report.
>
> If you have any test-case (script or whatever), please let me/us know.
>

Unfortunately not, I haven't reproduced it yet on my machines. But it 
seems that bug will hit only under heavy memory pressure. When close to 
OOM, or possibly with lots of writing to disk. It's also possible that 
fragmentation of memory zones could provoke it, that means testing it 
for a longer time.

-- 
Zlatko
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