revert work-around for bug 543617 please

[Kees Cook]

Hello,

I think that 5e1941884c700b7b97bcad52c2d8212ac56a7ebc is causing more
problems than it tries to solve[1].  i.e. if any filesystem is under heavy
load, you can't umount any other filesystems until the sync finishes.

Additionally, trivial stuff (even with an idle system) take an unexpectedly
long time (e.g. umount of a bind mount takes 1 second instead of nearly 0).

Try this in Karmic and Lucid:

sudo -s
mkdir -p /mnt/test
mount -o bind /tmp /mnt/test
time umount /mnt/test

Karmic: real    0m0.010s
Lucid: real    0m1.022s

-Kees

[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/543617

-- 
Kees Cook
Ubuntu Security Team