linux-kernel - Re: blk: NULL ptr deref in blk_dequeue

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Date:	Tue, 09 Oct 2012 09:26:24 -0400
From:	Sasha Levin <levinsasha928@...il.com>
To:	Jiri Kosina <jkosina@...e.cz>
CC:	Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
	axboe@...nel.dk, Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	ben@...adent.org.uk
Subject: Re: blk: NULL ptr deref in blk_dequeue_request()

On 10/09/2012 09:21 AM, Sasha Levin wrote:
> On 10/08/2012 05:45 PM, Jiri Kosina wrote:
>> On Mon, 8 Oct 2012, Jan Kara wrote:
>>
>>>>>> I'm still seeing this on linux-next.
>>>>   I think this is floppy related (see redo_fd_request() in the stack
>>>> trace). And there were quite some changes to the area recently. Adding
>>>> maintainer to CC.
>> Hmm ... I don't immediately see how this is happening.
>>
>> Sasha, could you please do git bisect on drivers/block/floppy.c between 
>> f6365201d and your git HEAD for starters (assuming that f6365201d works 
>> well for you?).
>>
> 
> A bisect on floppy.c yielded the following:
> 
> b33d002f4b6bae912463e5a66387c498aa69b6fe is the first bad commit
> commit b33d002f4b6bae912463e5a66387c498aa69b6fe
> Author: Ben Hutchings <ben@...adent.org.uk>
> Date:   Mon Aug 27 20:56:53 2012 -0300
> 
>     genhd: Make put_disk() safe for disks that have not been registered

2 more things:

 1. The guest vm which I'm testing on doesn't emulate anything which even looks like a floppy.
 2. I'm seeing the following lines before the BUG:

[    9.836604] floppy0: no floppy controllers found
[    9.837246] work still pending
[    9.837743] floppy0: floppy_shutdown: timeout handler died.


Thanks,
Sasha
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