How do I recover from Disk Utility hang without system restart?

Question

I have external CDROM connected to MBP and I wanted to read one data CD. The media was in bad shape (scratched) so macOS could not read anything. I wanted to eject the disk and try another media, just to find out I am completely stuck.

Disk Utility would spin "Loading disks" indefinitely, and all my efforts to unmount/eject disk from command line have failed. Not even eject button on CDROM drive worked. When I physically disconnected CDROM drive - diskutil still kept showing it:

/dev/disk6 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:        CD_partition_scheme                        *109.6 MB   disk6

With CDROM connected this did absolutely nothing:

drutil eject

I tried following with CDROM connected and disconnected (tldr; everything failed):

diskutil unmountDisk /dev/disk6
Unmount of disk6 failed: at least one volume could not be unmounted

diskutil umount force /dev/disk6
disk6 was already unmounted or it has a partitioning scheme so use "diskutil unmountDisk" instead

diskutil eject /dev/disk6
Volume timed out while waiting to eject

diskutil eject /dev/rdisk6
Volume timed out while waiting to eject

diskutil eject disk6
Volume timed out while waiting to eject

I issued sync to force cache flushing - it did nothing.

I checked all open handles with lsof - and could not find any.

This happened to me couple of times before due to bad (corrupted) USB drives (or HDD drives with esoteric Linux partition scheme), and only way I could get out of this type of hang was - reboot (not even logout/login worked).

Is there a way to recover from Disk Utility hang without system restart?

Only workaround I have so far is Windows in VM to do USB copying.

Any help would be appreciated.