[linux-lvm] Restoring snapshot gone bad

[Mauricio Tavares]

I have a lv, vmzone/desktop that I use as drive for a kvm guest;
nothing special here. I wanted to restore its snapshot so like I have
done many times before I shut guest down and then

lvconvert --merge vmzone/desktop_snap_20170921
  Logical volume vmzone/desktop is used by another device.
  Can't merge over open origin volume.
  Merging of snapshot vmzone/desktop_snap_20170921 will occur on next activation
 of vmzone/desktop.

What is it really trying to tell me? How to find out which other
device is using it?

lvdisplay tells me that

lvdisplay /dev/vmzone/desktop
  --- Logical volume ---
  LV Path                /dev/vmzone/desktop
  LV Name                desktop
  VG Name                vmzone
  LV UUID                3hcB1L-rIRf-PHZQ-I55F-ZXhT-SnSZ-vThO8U
  LV Write Access        read/write
  LV Creation host, time duocismj01e9se, 2017-06-29 15:07:12 -0400
  LV snapshot status     source of
                         desktop_snap_20170921 [active]
  LV Status              available
  # open                 2
  LV Size                100.00 GiB
  Current LE             25600
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           252:6

When I do plain old lvs (or lvs -a -o +devices), the attribute entry
for the desktop looks like

  desktop    vmzone    Owi-aos--- 100.00g

According to https://linux.die.net/man/8/lvs the "O" in Owi-aos--- means it
is merging a snapshot. But, what is its status? Based on how long it
has been that way, I think it is hung but I do not know what is
causing this hangup.

Suggestions?