linux-kernel - Re: 2.6.39-rc4 BUG: unable to handle kernel NULL pointer dereference at 0000000c IP: cfq_insert

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Date:	Thu, 21 Apr 2011 09:25:57 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Jens Axboe <JAxboe@...ionio.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.39-rc4 BUG: unable to handle kernel NULL pointer  dereference at  0000000c IP: cfq_insert_request+0x1d/0x3f5

On 21/04/2011, at 09.16, Michal Hocko <mhocko@...e.cz> wrote:

> On Wed 20-04-11 19:33:19, Jens Axboe wrote:
>> On 2011-04-20 15:29, Michal Hocko wrote:
>>> On Wed 20-04-11 15:13:15, Jens Axboe wrote:
>>>> On 2011-04-20 14:58, Michal Hocko wrote:
> [...]
>>>>> [   31.207888] Oops: 0000 [#1] PREEMPT [   31.208186] last sysfs file: /sys/devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0/block/sda/queue/scheduler
>>>> 
>>>> Ahh hang on, this may be a good clue. Does your boot scripts change the
>>>> IO scheduler?
>>> 
>>> Good one...
>>> Yes, I have:
>>> echo deadline > /sys/block/sda/queue/scheduler
>>> in /etc/rc.local
>>> 
>>> I am able to boot after I remove it. This is the first time I have seen
>>> "last sysfs file" being useful.
>>> Still want me to test the patch from the other email?
>> 
>> Is this a new addition to your system? IOW, how certain are you that
>> this is a regression that occured between rc3 and rc4?
> 
> No, I am setting the scheduler this way for quite some time. If I use it
> rc4 explodes while rc3 boots just fine. I am wondering, can this be a
> timing issue? I am able to set the scheduler after system settles down
> after boot and kde starts.
> 
> I am going to bisect, let's see if I can find anything.

Thanks, that would be great!

Jens

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