Created attachment 129131 [details]
serial terminal capture (power on, login, shutdown)

Hi,

this bug is similar to Bug 98200.

Since upgrade from kernel 4.8.17 to 4.9.{1,2,5} I am unable to restart or
shutdown my PC. 
Poweroff/restart always ends with black screen (display shows "no signal"). 
System stays frozen with fans / hard discs spinning. 
Reset button does not bring the system back - it stays completely frozen.
Only manual (power button) power off/on cycle brings the system back.

GPU: [AMD/ATI] Juniper XT [Radeon HD 5770]

I was able to capture kernel messages over serial line, last lines:

...
[  136.326236] systemd-shutdown[1]: All loop devices detached.
[  136.353887] kvm: exiting hardware virtualization
[  136.380090] Console: switching to colour VGA+ 80x25
[  136.406675] [drm] radeon: finishing device.  

I tested kernel 4.9.1, 4.9.2 and 4.9.5.