Re: GPF in __mark_inode_dirty due to locked_inode_to_wb_and_lock_list returning NULL

[Nikolay Borisov <kernel@kyup.com>]

On 07/01/2016 08:38 PM, Tejun Heo wrote:
> On Fri, Jul 01, 2016 at 12:00:50PM +0200, Jan Kara wrote:
>> Hello,
>>
>> On Thu 30-06-16 14:18:14, Nikolay Borisov wrote:
>>> In light of the discussion in https://patchwork.kernel.org/patch/9187411/ and 
>>> the discussion at https://groups.google.com/forum/#!topic/syzkaller/XvxH3cBQ134
>>
>> Well, it looks it is also some bdi_writeback lifetime issue but I don't see
>> how it would be related to I_DIRTY_TIME issues. There were couple of fixes
>> related to bdi_writeback issues from Tejun since 4.4. Maybe Tejun can tell
>> you whether he's seen this or not...
> 
> Yeah, this could be the same problem from the blkdev detach path.
> Nikolay, was there any block device hot unplugging going on?  If not,
> do you have a reproducer?

So the btrfs fs was created inside a loop device and mounted with -o loop. 
Evidently from the oops it seems that this is the normal umount path, meaning 
that no device hot plugging was in action. Unfortunately I don't have a reproducer. 
However, the workload looks like the following: 

1. mount -t btrfs -o compress=zlib -o subvol="${subvol}" -o loop "${storage_file}" "${mount_point}"
2. Do reads/writes (rsync) (dirtying some pages)
3. umount "${mount_point}"


> 
> Thanks.
>