vg_md0-swap: not deactivating: busy

[Towncat <towncat.towncat@gmail.com>]

I'm trying to deactivate a logical volume and the volume group it is
inside, but I get this error message (not exactly, I'm writing this
from memory). The point is, that the system thinks the swap partition
is in use. However, this is not the swap the system is using (that's
on another partition), and I turned even that off (swapoff). /proc/
swaps, swapon -s, ps xaf, lsof do not give a hint (to me) -- what
could be holding that logical volume? (The other lv on that vg can be
deactivated without a problem, that's root, also unused).

Thanks,
  tc