Comment # 2 on bug 99138 from Arthur Marsh

While bisecting an unrelated kernel bug I found that some kernels between 4.9.0
and 4.10-rc1 allowed:

service lxdm stop

to work as expected and cleanly stop the X server.

Otherwise either a kill -9 of the lxdm and Xorg process or a reboot is needed
to start the X server again.

If it would be helpful I could try bisecting to find the commit that stopped X
shutting down cleanly.