[linux-lvm] how to deactivate vg hosting root filesystem

["Joe Harvell" <harvell nortelnetworks com>]

So I set up an initrd that starts raid and lvm before doing a pivot_root
and execing init.  This has been working fine for a long time.

The only problem I have is that the only way I know of to free up the vg
for deactivation is to make init exit, which panics the kernel.  How do
I do this safely?