Bug#659762: snapshot removal bug work around.

[C. R. Meloche - CREDIL]

Problem affects removal attempt of a snapshot made from an mirrored lv. 
After removal attempt, all lv commands lock up, the rest of the system 
is operational, however a reboot is needed to free the lv commands and 
allow for the completion of the lv snapshot removal. (After reboot the 
lv is no longer a snapshot)

Here is a work around:

We need to do a dmsetup remove followed by lvremove twice:

lvcreate -L512M -s -n snapshotlv /dev/vgname/lvm-disk
   Logical volume "snapshot" created

dmsetup remove /dev/vgname/lvm-disk

lvremove -f vgname/snapshotlv
   Unable to deactivate open /vgname-lvm--disk--real (253:155)
   Failed to resume lvm-disk.

lvremove -f vgname/snapshotlv
   Logical volume "snapshotlv" successfully removed

I am a little concerned about the "Failed to resume lvm-disk." but I 
could not find any evidence that this was indeed the case, and even if 
it was, this state would last only a few ms.