https://bugs.freedesktop.org/show_bug.cgi?id=29556
--- Comment #9 from Alex Deucher agd5f@yahoo.com 2010-08-16 14:44:17 PDT --- (In reply to comment #8)
it happens on d-r-t since the blit the cleanup http://git.kernel.org/?p=linux/kernel/git/airlied/drm-2.6.git;a=commit;h=36d... I also have V2 of the cleanup (see comment #2) applied (and 2.6.35.2 also).
That patch is currently busted as is. You need to either revert it, or apply v2 that I posted on dri-devel.