Comment 6 for bug 558926

The problem seems to be that the kernel STILL can not properly force unmount. If I umount -f /dev/sr0 it fails with -EBUSY. A lazy umount leaves the filesystem still mounted. If I umount -l /dev/sr0 then try to open the drive in nautilus again I get:

Error mounting: mount exited with exit code 1: helper failed with:
mount: /dev/sr0 already mounted or /media/cdrom0 busy

As long as a process keeps an open fd, the filesystem remains mounted ( but hidden from the namespace ), which prevents you from mounting it again, even if new media has been inserted. You also can not use lsof to find what process still has files open since they have been removed from the namespace.

There also does not seem to be a way to undo a lazy umount and reattach the mount point to the namespace.