Comment 10 for bug 1181528

Easily reproduced here, by (a) having two or more non-root filesystems mounted, (b) deleting all *pack files from /var/lib/ureadahead. The second reboot will fail to unmount the root.

The patch I've added to bug #1181789 seems to be the correct answer, but the attached patch to the ureadahead upstart job should be an effective workaround with no side effects.