btrfs qgroup destroy -> ERROR: unable to create quota group: Device or resource busy

[Tomasz Chmielewski <tch@virtall.com>]

I'm using qgroups and have created a few hundreds of subvolumes in the
past.

It seems that btrfs automatically assigns a qgroup to newly created
snapshot/subvolume, but does not destroy the qgroup when the subvolume
is deleted.

So I've tried to destroy the unused qgroups, with mixed success. I was
able to destroy most of them, but some are still failing, i.e.:

# btrfs qgroup destroy 4494 /mnt/lxc1
ERROR: unable to create quota group: Device or resource busy


Note the negative number here, but I also have qgroups with both
positive numbers, which I'm not able to destroy as well:

# btrfs qgroup show /mnt/lxc1 | grep 4494
0/4494 839516160 -69632


qgroup 4494 is not used by any subvolume:

# btrfs sub list /mnt/lxc1 | grep 4494


I did run "btrfs quota rescan" for this filesystem, hoping it will fix
the problem, but it didn't.


Any advice?


-- 
Tomasz Chmielewski
http://wpkg.org