Created attachment 120925 [details]
Kernel dmesg around the time of the lockup.

After a period of time playing the latest version of TF2, my GPU locks up. 
After the kernel tries to reset, the X becomes stuck and won't work.  The rest
of the system is fine however.  Sometimes, the GPU will reset successfully and
continue working, only to lockup later, eventually freezing X.

Hardware:
GPU: Gigabyte Radeon HD 7970 Ghz edition OC
CPU: AMD Phenom ii X6 1100T
MB: Asus Crosshair IV Formula

Software:
Mesa: 11.1.0
DRM: 2.4.65
LLVM: 3.7.0
X: 1.17.4
DDX: 7.6.1
Kernel: 4.3.3

I have a dmesg with debug turned on and a strace of X from around the time it
crashes (attached).  I reduced the log file to the relevant bits, as they are
quite large.  I'll retry with latest git, see if it helps anywhere.