Ejecting a CD with the hardware drive button only causes a change uevent, but
the device node stays around (just without a medium). Pick up these uevents and
mark the device as SYSTEMD_READY=0 on ejection, so that systemd stops the
device unit and consequently all mount units on it.
On media insertion, mark the device as SYSTEMD_READY=1 again.
https://bugs.freedesktop.org/show_bug.cgi?id=72206
https://bugzilla.opensuse.org/show_bug.cgi?id=909418
https://bugs.archlinux.org/task/42071
https://bugs.launchpad.net/bugs/
1168742
# enable the receiving of media eject button events
IMPORT{program}="cdrom_id --lock-media $devnode"
+# ejecting a CD does not remove the device node, so mark the systemd device
+# unit as inactive while there is no medium; this automatically cleans up of
+# stale mounts after ejecting
+ENV{DISK_MEDIA_CHANGE}=="?*", ENV{ID_CDROM_MEDIA}!="?*", ENV{SYSTEMD_READY}="0"
+
KERNEL=="sr0", SYMLINK+="cdrom", OPTIONS+="link_priority=-100"
LABEL="cdrom_end"