[linux-lvm] Resizing a logical volume which is mounted (at /home)

[Kiran Rao <techie curious gmail com>]

To start off, here's an overview of my configuration. I'm dual-booting 
Windows XP and Fedora Core 16. When I installed FC 16, here's how I 
created the partitions:

1) Volume Group (vg_me) - ~73 GB

Out of this, the following are the logical volumes:
a) lvhome (mount point - /home) - ~48GB
b) lvroot (mount point - /) ~10GB
c) lvvar (mount point - /var) ~15GB

So, there's no free space left on the volume group.

Now, I feel the 48GB is not really necessary for the /home. I want 
to redistribute the space among the 3 logical volumes within this VG, or
 create a new one (/tech).  In either case, I want to take the 
additional space (around 20GB) from lvhome and give it to either / or to
 /tech.

Now, I tried the GUI (system-config-lvm) tool to do this. I can 
click on lvhome and try to resize it. However, the problem is that since
 I am logged in as a non-root user, the /home is mounted. Resizing 
requires one to unmount it, but the unmount operation fails since I am 
mounted.

How do I work around this?