[BUG] 4.14 regression: Xorg hangs on exit

[Bob Tracy]

Apologies for the lack of detail, but the subject pretty much says it
all.  Xorg works fine with 4.13, but hangs on exit with 4.14.

Logging in remotely and applying the "kill -9" sledgehammer has no
effect.  System logs don't show anything unusual going on.  Rebooting
hangs because of the unkillable process: hitting the reset switch is
the only way forward.

Video driver is "radeon", reporting "ATOM BIOS: REDWOOD" at boot time.
Console is fb0 == radeondrmfb.

--Bob