Same problem here on a fedora 23

GPU: HD 7970
CPU: Intel Core i7 950

Mesa 11.1.0
DRM 2.43.0
LLVM 3.7.0
kernel: 4.3.4

The logs are filed with "ring stalled" and GPU lock messages. I can send more
logs if needed.

radeon 0000:02:00.0: ring 3 stalled for more than 10249msec
radeon 0000:02:00.0: GPU lockup (current fence id 0x000000000001e5f1 last fence
id 0x000000000001e5f2 on ring 3)

I've tried a different firmware
(http://people.freedesktop.org/~agd5f/radeon_ucode/k/) which seemed to have
helped other people with their own problem but it didn't help in my case.

Does it makes sense to try to rollback to an older kernel?