Found the following in kernel logs:
May 02 23:37:31 GetsugaTenshou kernel: radeon 0000:01:00.0: ring 0 stalled for
more than 10052msec
May 02 23:37:31 GetsugaTenshou kernel: radeon 0000:01:00.0: GPU lockup (current
fence id 0x00000000000121ff last fence id 0x0000000000012209 on ring 0)
May 02 23:37:31 GetsugaTenshou kernel: radeon 0000:01:00.0: ring 4 stalled for
more than 10084msec
May 02 23:37:31 GetsugaTenshou kernel: radeon 0000:01:00.0: GPU lockup (current
fence id 0x000000000000b547 last fence id 0x000000000000b548 on ring 4)
May 02 23:37:31 GetsugaTenshou kernel: radeon 0000:01:00.0: ring 3 stalled for
more than 10128msec
May 02 23:37:31 GetsugaTenshou kernel: radeon 0000:01:00.0: GPU lockup (current
fence id 0x0000000000002c7c last fence id 0x0000000000002c7d on ring 3)