I spent the afternoon bisecting the kernel and found the commit seeming to
cause the GPU lockups

4ac0533abaec2b83a7f2c675010eedd55664bc26 is the first bad commit
commit 4ac0533abaec2b83a7f2c675010eedd55664bc26
Author: Jerome Glisse <jglisse@redhat.com>
Date:   Thu Dec 13 12:08:11 2012 -0500

    drm/radeon: fix htile buffer size computation for command stream checker

    Fix the size computation of the htile buffer.

    Signed-off-by: Jerome Glisse <jglisse@redhat.com>
    Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

:040000 040000 cf30bb09a4096c41959a27c6fc7d391dfa718028
fc571d6379b3b697a2bad0e5d097797f77c0a1b6 M      drivers