drm: Only evict the blocks required to create the requested hole

drm: Only evict the blocks required to create the requested hole

Avoid clobbering adjacent blocks if they happen to expire earlier and
amalgamate together to form the requested hole.

In passing this fixes a regression from
commit ea7b1dd44867e9cd6bac67e7c9fc3f128b5b255c
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Feb 18 17:59:12 2011 +0100

    drm: mm: track free areas implicitly

which swaps the end address for size (with a potential overflow) and
effectively causes the eviction code to clobber almost all earlier
buffers above the evictee.

v2: Check the original hole not the adjusted as the coloring may confuse
us when later searching for the overlapping nodes. Also make sure that
we do apply the range restriction and color adjustment in the same
order for both scanning, searching and insertion.

v3: Send the version that was actually tested.

Note that this seems to be ducttape of decent quality ot paper over
some of our unbind related gpu hangs reported since 3.7. It is not
fully effective though, and certainly doesn't fix the underlying bug.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
[danvet: Added note plus bugzilla link and tested-by.]
Cc: stable@vger.kernel.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=55984
Tested-by:  Norbert Preining <preining@logic.at>
Acked-by: Dave Airlie <airlied@gmail.com
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>