drm/i915: Check fence status on every pin.

As we may steal the fence register of an unpinned buffer for another,
every time we repin the buffer we need to recheck whether it needs to be
allocated a fence.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_gem.c

@@ -2730,14 +2730,21 @@ i915_gem_object_pin(struct drm_gem_object *obj, uint32_t alignment)
 				DRM_ERROR("Failure to bind: %d\n", ret);
 			return ret;
 		}
+	}
 	/*
 	 * Pre-965 chips need a fence register set up in order to
 	 * properly handle tiled surfaces.
 	 */
 	if (!IS_I965G(dev) &&
 	    obj_priv->fence_reg == I915_FENCE_REG_NONE &&
-		    obj_priv->tiling_mode != I915_TILING_NONE)
-			i915_gem_object_get_fence_reg(obj, true);
+	    obj_priv->tiling_mode != I915_TILING_NONE) {
+		ret = i915_gem_object_get_fence_reg(obj, true);
+		if (ret != 0) {
+			if (ret != -EBUSY && ret != -ERESTARTSYS)
+				DRM_ERROR("Failure to install fence: %d\n",
+					  ret);
+			return ret;
+		}
 	}
 	obj_priv->pin_count++;