Re: [PATCH 0/3] btrfs: allow BTRFS_IOC_SNAP_DESTROY_V2 to remove ghost subvolume

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2021/7/20 下午12:05, Zygo Blaxell wrote:
> On Mon, Jun 28, 2021 at 06:16:34PM +0800, Qu Wenruo wrote:
>> Since we're busting ghost subvolumes, the branch is now called
>> ghost_busters:
>> https://github.com/adam900710/linux/tree/ghost_busters
>>
>> The first two patches are just cleanup found during the development.
>>
>> The first is a missing check for subvolid range, the missing check
>> itself won't cause any harm, just returning -ENOENT from dentry lookup,
>> other than the expected -EINVAL.
>>
>> The 2nd is a super old dead comment from the early age of btrfs.
>>
>> The final patch is the real work to allow patched "btrfs subvolume delete -i"
>> to delete ghost subvolume.
>> Tested with the image dump of previous submitted btrfs-progs patchset.
>>
>> Qu Wenruo (3):
>>    btrfs: return -EINVAL if some user wants to remove uuid/data_reloc
>>      tree
>>    btrfs: remove dead comment on btrfs_add_dead_root()
>>    btrfs: allow BTRFS_IOC_SNAP_DESTROY_V2 to remove ghost subvolume
>
> I hit this bug on several machines while they were running 5.11.  The
> ghost subvols seem to occur naturally--I didn't change my usual workloads
> to get them, they just showed up in fairly normal snapshot rotation.

And there is no powerloss involved?

Then it's a much serious problem than I thought.

Thanks,
Qu
>
> They don't seem to occur on 5.10 (up to .46) or on 5.12 and later, but
> once they are created, they don't go away without using this patch to
> remove them.
>
> This patch does get rid of the ghost subvols after the fact, quite nicely.
>
> Some users on IRC have hit the same problem.  One was running Debian's
> backported 5.10, which doesn't fit the pattern of kernel versions I've
> observed, but maybe Debian backported something?
>
>>   fs/btrfs/ioctl.c       | 81 +++++++++++++++++++++++++++++++++++++++++-
>>   fs/btrfs/transaction.c |  7 ++--
>>   2 files changed, 84 insertions(+), 4 deletions(-)
>>
>> --
>> 2.32.0
>>
>