Comment 27 for bug 1755863

With systemd on Xenial & Artful, there is no instruction in the case of MOUNT_MOUNTING which re-enforce why it is working with these releases :

# src/core/mount.c
1182 case MOUNT_MOUNTING:
1183 case MOUNT_MOUNTING_DONE:
1184 case MOUNT_MOUNTING_SIGKILL:
1185 case MOUNT_MOUNTING_SIGTERM:
1186
1187 if (f == MOUNT_SUCCESS)
1188 mount_enter_mounted(m, f);
1189 else if (m->from_proc_self_mountinfo)
1190 mount_enter_mounted(m, f);
1191 else
1192 mount_enter_dead(m, f);
1193 break;

So most likely, falls in the MOUNT_MOUNTING_SIGTERM and then break the case statement flow.

# src/basic/unit-def.h
MOUNT_MOUNTING, /* /usr/bin/mount is running, but the mount is not done yet. */