Re: BZ#101951, Overlayfs on top of btrfs causes kernel oops + freeze

[Colin Ian King <colin.king@canonical.com>]

On 16/02/16 16:11, Filipe Manana wrote:
> On Tue, Feb 16, 2016 at 4:08 PM, Colin Ian King
> <colin.king@canonical.com> wrote:
>> On 16/02/16 15:51, Filipe Manana wrote:
>>> On Tue, Feb 16, 2016 at 3:38 PM, Colin Ian King
>>> <colin.king@canonical.com> wrote:
>>>> Hi there,
>>>>
>>>> bug: https://bugzilla.kernel.org/show_bug.cgi?id=101951 and also
>>>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1532145
>>>>
>>>> Commit 4bacc9c9234c7c8eec44f5ed4e960d9f96fa0f01 ("overlayfs: Make f_path
>>>> always point to the overlay and f_inode to the underlay") resulted in an
>>>> issue when using a combination of btrfs and overlayfs.  This is
>>>> noticeable when doing a fsync() on a file in a chroot with overlayfs on
>>>> top of btrfs; we hit a kernel oops in btrfs_sync_file() on
>>>> atomic_inc(&root->log_batch) because root is NULL.
>>>>
>>>> I've debugged this further and found that in btrfs_sync_file():
>>>>
>>>>         struct inode *inode = d_inode(dentry);
>>>>
>>>> does not return the inode I expected when using the stacked overlay fs,
>>>> where as:
>>>>
>>>>         struct inode *inode = file_inode(file);
>>>>
>>>> does.
>>>
>>> See the discussion at
>>> https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg48131.html
>>>
>>> You can get along with file_inode() in btrfs_sync_file(), but not
>>> later the fsync code path where we traverse the hierarchy up using
>>> dentries.
>>> More details on that thread.
>>
>> Ah, good. So was there any resolution on a way forward for a fix?
> 
> Nop.
> 
OK, so chroots don't work, that's a bit of a show stopper :-/

>>
>>>
>>>>
>>>> However, I'm not well at all well versed in btrfs, so I am not confident
>>>> this is a actually correct.  Any comments?
>>>>
>>>> Colin
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>>>
>>>
>>>
>>
> 
> 
>