systemd: autofs containing autofs does not unmount

I'm trying to set up two directories, each automounted: * /mnt/dir * /mnt/dir/subdir In my case, these are: * /mnt/btrfs-vol/rootfs (read only) * /mnt/btrfs-vol/rootfs/btrbk-snap (RW for taking snapshots with [btrbk](https://github.com/digint/btrbk)) My /etc/fstab contains: LABEL=rootfs /mnt/btrfs-vol/rootfs btrfs ro,subvol=/,lazytime,compress=lzo,ssd,discard,noauto,x-systemd.automount,x-systemd.idle-timeout=2 LABEL=rootfs /mnt/btrfs-vol/rootfs/btrbk-snap btrfs rw,subvol=/btrbk-snap,lazytime,compress=lzo,ssd,discard,noauto,x-systemd.automount,x-systemd.idle-timeout=2,x-systemd.requires-mounts-for=/mnt/btrfs-vol/rootfs I do: svelte ~# systemctl daemon-reload && systemctl restart local-fs.target svelte ~# mount | grep btrfs-vol/rootfs systemd-1 on /mnt/btrfs-vol/rootfs type autofs (rw,relatime,fd=32,pgrp=1,timeout=2,minproto=5,maxproto=5,direct) Strangely, /mnt/btrfs-vol/rootfs, is already mounted. If I unmount /mnt/btrfs-vol/rootfs, it is immediately remounted: svelte ~# umount /mnt/btrfs-vol/rootfs svelte ~# mount | grep btrfs-vol/rootfs systemd-1 on /mnt/btrfs-vol/rootfs type autofs (rw,relatime,fd=32,pgrp=1,timeout=2,minproto=5,maxproto=5,direct) Now if I ping the subdirectory, it automounts: svelte ~# (cd /mnt/btrfs-vol/rootfs/btrbk-snap/ && mount | grep btrfs-vol/rootfs) systemd-1 on /mnt/btrfs-vol/rootfs type autofs (rw,relatime,fd=32,pgrp=1,timeout=2,minproto=5,maxproto=5,direct) /dev/mapper/vg_svelte-rootfs on /mnt/btrfs-vol/rootfs type btrfs (ro,relatime,lazytime,compress=lzo,ssd,discard,space_cache,subvolid=5,subvol=/) Note that the fstype of /dev/mapper/vg_svelte-rootfs has changed from autofs to btrfs. A few seconds later (I have timeout=2 for testing`): svelte ~# mount | grep btrfs-vol/rootfssystemd-1 on /mnt/btrfs-vol/rootfs type autofs (rw,relatime,fd=32,pgrp=1,timeout=2,minproto=5,maxproto=5,direct) The subdirectory is unmounted, and the fstype of /dev/mapper/vg_svelte-rootfs reverts to autofs, *but it stays mounted*. **How do I get it to automatically unmount?** Possibly useful information: journal output: Feb 21 17:16:07 svelte systemd: Reloading. Feb 21 17:16:23 svelte systemd: Mounting /mnt/btrfs-vol/rootfs... Feb 21 17:16:23 svelte systemd: Set up automount mnt-btrfs\x2dvol-home-btrbk\x2dsnap.automount. Feb 21 17:16:23 svelte systemd: Mounted /mnt/btrfs-vol/rootfs. Feb 21 17:16:23 svelte systemd: mnt-btrfs\x2dvol-rootfs-btrbk\x2dsnap.automount: Directory /mnt/btrfs-vol/rootfs/btrbk-snap to mount over is not empty, mounting anyway. Feb 21 17:16:23 svelte systemd: Set up automount mnt-btrfs\x2dvol-rootfs-btrbk\x2dsnap.automount. Feb 21 17:16:23 svelte systemd: Reached target Local File Systems. Feb 21 17:16:25 svelte systemd: Stopped target Local File Systems. Feb 21 17:16:25 svelte systemd: Unset automount mnt-btrfs\x2dvol-rootfs-btrbk\x2dsnap.automount. Feb 21 17:16:25 svelte systemd: Unmounting /mnt/btrfs-vol/rootfs... Feb 21 17:16:25 svelte systemd: Unmounted /mnt/btrfs-vol/rootfs. Feb 21 17:17:44 svelte systemd: Unset automount mnt-btrfs\x2dvol-home-btrbk\x2dsnap.automount. Checking that nothing has the directory open: svelte ~# lsof /mnt/btrfs-vol/rootfs lsof: WARNING: can't stat() fuse.gvfsd-fuse file system /run/user/1000/gvfs Output information may be incomplete. svelte ~# ls -l /run/user/1000 | grep gvfs ls: cannot access '/run/user/1000/gvfs': Permission denied d????????? ? ? ? ? ? gvfs I've never seen ? where I'd expect the rwx placehoders to be before.