drm/i915: Only clear the GPU domains upon a successful finish

By clearing the GPU read domains before waiting upon the buffer, we run
the risk of the wait being interrupted and the domains prematurely
cleared. The next time we attempt to wait upon the buffer (after
userspace handles the signal), we believe that the buffer is idle and so
skip the wait.

There are a number of bugs across all generations which show signs of an
overly haste reuse of active buffers.

Such as:

  https://bugs.freedesktop.org/show_bug.cgi?id=29046
  https://bugs.freedesktop.org/show_bug.cgi?id=35863
  https://bugs.freedesktop.org/show_bug.cgi?id=38952
  https://bugs.freedesktop.org/show_bug.cgi?id=40282
  https://bugs.freedesktop.org/show_bug.cgi?id=41098
  https://bugs.freedesktop.org/show_bug.cgi?id=41102
  https://bugs.freedesktop.org/show_bug.cgi?id=41284
  https://bugs.freedesktop.org/show_bug.cgi?id=42141

A couple of those pre-date i915_gem_object_finish_gpu(), so may be
unrelated (such as a wild write from a userspace command buffer), but
this does look like a convincing cause for most of those bugs.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org
Reviewed-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: NEugeni Dodonov <eugeni.dodonov@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -3064,10 +3064,13 @@ i915_gem_object_finish_gpu(struct drm_i915_gem_object *obj)
 			return ret;
 	}
 
+	ret = i915_gem_object_wait_rendering(obj);
+	if (ret)
+		return ret;
+
 	/* Ensure that we invalidate the GPU's caches and TLBs. */
 	obj->base.read_domains &= ~I915_GEM_GPU_DOMAINS;
-
-	return i915_gem_object_wait_rendering(obj);
+	return 0;
 }
 
 /**