Comment # 3 on bug 1201114 from Stanislav Brabec

This is very strange:

Jul 07 13:52:20 Mobile-PC kernel: BTRFS warning: duplicate device /dev/sdc2
devid 1 generation 6733 scanned by mount (4717)

It looks that even if everything was correctly unmounted, something in the
kernel still holds a record for /dev/sdb2, which prevents it from releasing.


Just a dumb idea:

What happens if you do rmdir /mnt/chroot after unplug, but before replug. It
seems, that something becomes bound to this directory, but it is not a mounted
volume.

Does the bug happens then? Does the device get name sdb2 or sdc2 then?

In any case, it looks like a kernel problem that has nothing to do with
mount/libmount.