That line above will end with “rw discard_passdown queue_if_no_space ” on a healthy (working) system. If there’s the ‘ro’ there, that means your thin-pool is flagged for a check.
Similar to how an improperly unmounted filesystem requires a check. To clear that out and return to normal operations follow this procedure:
# systemctl stop docker.service
# thin_check /var/lib/docker/devicemapper/
If there were no errors then proceed with:
# thin_check –clear-needs-check-flag /var/lib/docker/devicemapper/
# systemctl start docker.service
# docker run –name=fpm-5.3 debian:jessie
If there were errors, you are on your own, but ‘man thin_check’ and ‘man thin_repair’ may be helpful…