How to extend root LV that is being used as a snapshot origin volume

Issue

• If the logical volume containing the root filesystem is a snapshot origin volume, trying to extend it fails with the following error:

# lvextend -l +100%free /dev/mapper/rhel-root
  Snapshot origin volumes can be resized only while inactive: try lvchange -an.

• However, trying to deactivate the logical volume fails as well:

# lvchange -an /dev/mapper/rhel-root
  Logical volume rhel/root contains a filesystem in use.

• Since the root filesystem can not be unmounted, how can the root filesystem's logical volume be extended if it is a snapshot origin volume?