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

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Message-ID: <CA+icZUWMrZSh_0Lc3kGXsjMYZeBhuJx7ia6rs+CyW=yFb7bdxQ@mail.gmail.com>
Date:	Fri, 28 Dec 2012 01:56:08 +0100
From:	Sedat Dilek <sedat.dilek@...il.com>
To:	Zlatko Calusic <zlatko.calusic@...on.hr>
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 Fri, Dec 28, 2012 at 1:42 AM, Zlatko Calusic <zlatko.calusic@...on.hr> wrote:
> On 28.12.2012 01:37, Sedat Dilek wrote:
>>
>> On Fri, Dec 28, 2012 at 1:33 AM, Zlatko Calusic <zlatko.calusic@...on.hr>
>> wrote:
>>>
>>> On 28.12.2012 01:24, Sedat Dilek wrote:
>>>>
>>>>
>>>> On Fri, Dec 28, 2012 at 12:51 AM, Zlatko Calusic
>>>> <zlatko.calusic@...on.hr> wrote:
>>>>>
>>>>>
>>>>> 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.
>>>>>
>>>>
>>>> I tested successfully by doing simultaneously...
>>>> - building Freetz with 8 parallel make-jobs
>>>> - building Linux GIT with 1 make-job
>>>> - 9 tabs open in firefox
>>>> - In one tab I ran YouTube music video
>>>> - etc.
>>>>
>>>> I am reading [1] and [2] where another user reports success by reverting
>>>> this...
>>>>
>>>> commit cda73a10eb3f493871ed39f468db50a65ebeddce
>>>> "mm: do not sleep in balance_pgdat if there's no i/o congestion"
>>>>
>>>> BTW, this machine has also 4GiB RAM (Ubuntu/precise AMD64).
>>>>
>>>> Feel free to add a "Reported-by/Tested-by" if you think this is a
>>>> positive report.
>>>>
>>>
>>> Thanks for the testing! And keep running it in case something interesting
>>> pops up. ;)
>>>
>>> No need to revert cda73a10eb because it fixes another bug. And the patch
>>> you're now running fixes the new bug I introduced with a combination of
>>> my
>>> latest 2 patches. Nah, it gets complicated... :)
>>>
>>> But, at least I found the culprit and as soon as Linus applies the fix,
>>> everything will be hunky dory again, at least on this front. :P
>>>
>>
>> I am not subscribed to LKML and linux-mm,,,
>> Do you have a patch with a proper subject and descriptive text? URL?
>>
>
> Soon to follow. I'd appreciate Zhouping Liu testing it too, though.

I understand, but I want to push your patch with a proper subject-line
as a pending patch with reference to patchwork, so...

- Sedat -

> --
> Zlatko
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