Created attachment 80920 [details]
netconsole.log

I've been able to get a more complete output using netconsole. I'm not sure if
it helps, but here it is.

Here are the steps to reproduce the crash:

1) Go to youtube.com, start playing a video.
   => This prints these lines:
      radeon 0000:01:00.0: GPU fault detected: 146 0x0b95e004
      radeon 0000:01:00.0:   VM_CONTEXT1_PROTECTION_FAULT_ADDR   0x000010B9
      radeon 0000:01:00.0:   VM_CONTEXT1_PROTECTION_FAULT_STATUS 0x050E0004
2) Close the web browser, activate xscreensaver with an opengl screensaver like
photopile.
   => GPU lockup CP stall