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

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Date:	Fri, 28 Dec 2012 14:43:24 +0100
From:	Zlatko Calusic <zlatko.calusic@...on.hr>
To:	Zhouping Liu <zliu@...hat.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Johannes Weiner <jweiner@...hat.com>, mgorman@...e.de,
	hughd@...gle.com, Andrea Arcangeli <aarcange@...hat.com>,
	Hillf Danton <dhillf@...il.com>, sedat.dilek@...il.com
Subject: Re: BUG: unable to handle kernel NULL pointer dereference at 0000000000000500

On 28.12.2012 10:01, Zhouping Liu wrote:
> On 12/28/2012 10:45 AM, Zhouping Liu wrote:
>>> Thank you for the report Zhouping!
>>>
>>> Would you be so kind to test the following patch and report results?
>>> Apply the patch to the latest mainline.
>> Hello Zlatko,
>>
>> I have tested the below patch(applied it on mainline directly),
>> but IMO, I'd like to say it maybe don't fix the issue completely.
>
> Hi Zlatko,
>
> I re-tested it on another machine, which has 60+ Gb RAM and 4 numa nodes,
> without your patch, it's easy to reproduce the 'NULL pointer' error,
> after applying your patch, I couldn't reproduce the issue any more.
>
> depending on the above, it implied that your patch fixed the issue.
>

Yes, that's exactly what I expected. Just wanted to doublecheck this 
time. Live and learn. ;)

> but in my last mail, I tested it on two machines, which caused hung task
> with your patch,
> so I'm confusing is it your patch block some oom-killer performance? if
> it's not, your patch is good for me.
>

 From what I know, the patch shouldn't have much influence on the oom 
killer, if any. But, as all those subsystems are closely interconnected, 
both oom & vmscan code is mm after all, there could be some 
interference. Is the hung-task issue repeatable?
-- 
Zlatko
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