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

[Sedat Dilek <sedat.dilek@gmail.com>]

On Fri, Dec 28, 2012 at 1:33 AM, Zlatko Calusic <zlatko.calusic@iskon.hr> wrote:
> On 28.12.2012 01:24, Sedat Dilek wrote:
>>
>> On Fri, Dec 28, 2012 at 12:51 AM, Zlatko Calusic
>> <zlatko.calusic@iskon.hr> wrote:
>>>
>>> On 28.12.2012 00:42, Sedat Dilek wrote:
>>>>
>>>>
>>>> On Fri, Dec 28, 2012 at 12:39 AM, Zlatko Calusic
>>>> <zlatko.calusic@iskon.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?

- Sedat -

> Thanks,
> --
> Zlatko

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