Description:
Running a server with multiple docker containers deployed by docker-compose. After some days/weeks/months, I want to reboot the server. Before rebooting, I am trying to cleanly stop and unmount everything. After stopping docker, there are some overlay2 mountpoints left over which prevent to unmount the underlying filesystem which eventually lets the whole server hang on shutdown.

How can I figure out where the issue is and/or whether this is a bug?

Additional info:
* package version(s)
community/docker 1:19.03.5-1 [installed]


Steps to reproduce:
Not sure if that helps, because it does not seem to be always reproducible:

1) boot server
2) decrypt volumes
3) mount fs
4) start docker
5) start containers
6) wait
7) stop docker
8) mount | grep overlay2


umount /mnt/data fails because there are left over mounts in /mnt/data/docker

workaround:

for m in `mount | grep overlay | awk '{ print $3 }'`; do umount $m;done
for m in `mount | grep nsfs | awk '{ print $3 }'`; do umount $m;done
for m in `mount | grep shm | awk '{ print $3 }'`; do umount $m;done

followed by:

umount /mnt/data