Comment # 10 on bug 1137390 from Neil Brown

> # systemctl show mnt.mount | egrep 'RequiredBy|WantedBy'
> RequiredBy=mnt-tahan.mount mnt-tahan-01_RSH.mount

So, where are these units coming from..

 systemctl show mnt-tahan.mount | grep Path=

might help.

> I thought the Options= line in /run/systemd/generator/mnt.mount was weird with a 'fg' and 'bg'

Weird, but normal.  The "bg" option tells mount.nfs to fork and continue in the
background.  systemd doesn't like mount programs doing this.  Systemd would
rather do the job management itself.
So when systemd-fstab-generator sees "bg" it adds
  x-systemd.mount-timeout=infinity,retry=10000
to the start, and
  fg
to the end.  The timeouts cause systemd to impose the same timeouts as
mount.nfs would normally assume, the "fg" at the end causes mount.nfs to ignore
the "bg" (last option wins).