Unable to unmount 'hung NFS mount' (server gone) with FORCE and/or LAZY

[Sander Smeenk]

Ubuntu Trusty, util-linux 2.20.1-5.1ubuntu20.3

I can't 'umount -f /mnt/storage' an NFS-filesystem whose remote end has gone missing. The process just stalls in an uninterruptable state. Strace shows umount at some point tries to readlink() the mount point which stalls because that mount point is broken. Which is why i want to force umount it. ;)

I then proceeded to remove 99% of umount.c's code so it would just call umount2() on the target with the FORCE flag, recompiled the binary and it 'neatly' unmounted the filesystem.

I think umount.c tries too many sanity checks with -f enabled.
It should perhaps ask if the user is really sure, and then just call umount on the target and fix mtab etc...