Bug#251425: Dangerous /etc/mtab setup on reboot.
[..] remote filesystems are unmounted
first, so the node's private /etc is unmounted and the shared root and
its /etc directory becomes visible again [..] When init.d/umountfs runs,
'mount' does not see the local filesystems mounted in the node, and the
system is rebooted without unmounting them, which may lead to serious data
loss and filesystem corruption. [..]
This is a problem.
But isn't another option to just have the order of unmount operations
reversed for diskless nodes? It seems to me that it would be better
for "diskless" nodes to unmount local file systems first, and then network
file systems. Wouldn't that solve the problem equally well?