lvm is great for creating logical volumes for vps installations on xen. i created a snapshot for doing a backup of one of the vps systems from domain-0, then when i was done, i tried to remove the snapshot with lvremove and the command never finished. later, i found out that any kernel after 2.6.15 requires lvm greater than 2.01 and devmapper greater than 1.01 to avoid such an uninterruptible hang.
here's some info about how i created the snapshot and recovered from the hang error.

here's the setup that led to the problem:
kernel running on a debian sarge distro.
lvm2 from sarge installed the following:

The solution is to upgrade to lvm 2.02 or greater and devmapper 1.02 or greater. If you're running sarge, one solution is to read this blog entry and use the debs that Jürgen has kindly provided.
Thanks Jürgen Kreileder

uname -a
Linux localhost #1 SMP Mon Jan 8 14:39:02 GMT 2007 i686 GNU/Linux

lvm version
  LVM version:     2.01.04 (2005-02-09)
  Library version: 1.01.00-ioctl (2005-01-17)
  Driver version:  4.5.0

#this command with the above version of lvm caused a hang
lvremove /dev/vg01/tempsnap

#to use the debs, perform the following
#add the following lines to /etc/apt/sources.list

deb sarge main
deb-src sarge main

#execute the following so apt knows about the blackdown debs
apt-get update

#if you want to see what it will do first, use apt-get -s
apt-get -s install lvm2 libdevmapper1.02 lvm-common

#then install it for real
apt-get install lvm2 libdevmapper1.02 lvm-common

#then you can check the installed version with
lvm version
  LVM version:     2.02.02 (2006-02-07)
  Library version: 1.02.03 (2006-02-08)
  Driver version:  4.5.0

#the following debs were installed