Re: [PATCH] block: return EBUSY from drop_partitions on mounted whole disk device

[Jens Axboe <axboe@kernel.dk>]

On 03/02/2016 03:13 PM, Eric Sandeen wrote:
>
>
> On 3/1/16 2:45 PM, Eric Sandeen wrote:
>> On 8/5/15 2:13 PM, Eric Sandeen wrote:
>>> The BLKRRPART ioctl already fails today if any partition under
>>> the device is mounted.  However, if we mkfs a whole disk and mount
>>> it, BLKRRPART happily proceeds down the invalidation path, which
>>> seems like a bad idea.
>>>
>>> Check whether the whole device is mounted by checking bd_super,
>>> and return -EBUSY if so.
>>>
>>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
>>> ---
>>>
>>> I don't know for sure if this is the right approach, but figure
>>> I'll ask in the form of a patch.  ;)
>>
>> I'm now thinking that this is not the right approach.  :(  I got a
>> bug report stating that during some md raid1 testing with replacing
>> failed disks, filesystems were losing data.  I haven't reproduced
>> that part yet, but...
>>
>> It's hitting the "bd_super" case added in the patch below, and returning
>> -EBUSY to md when mdadm tries to to remove a disk:
>>
>> # mdadm /dev/md0 -r /dev/loop0
>> mdadm: hot remove failed for /dev/loop0: Device or resource busy
>
> FWIW, just ignore me, I was being an idiot.  a) the patch *prevents*
> the corruption; does not cause it; without the EBUSY, drop_partitions
> will get to invalidate_inodes() etc, and no wonder data is lost.
> And b) the above EBUSY is because I forgot to fail the disk first. :/
>
> Nothing to see here, move along, sorry!

Still beats a regression :-)

-- 
Jens Axboe