drm/i915: Guard pages being reaped by OOM whilst binding-to-GTT

In the circumstances that the shrinker is allowed to steal the mutex
in order to reap pages, we need to be careful to prevent it operating on
the current object and shooting ourselves in the foot.
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2925,6 +2925,8 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 	if (ret)
 		return ret;
 
+	i915_gem_object_pin_pages(obj);
+
  search_free:
 	if (map_and_fenceable)
 		free_space =
@@ -2955,14 +2957,17 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 					       obj->cache_level,
 					       map_and_fenceable,
 					       nonblocking);
-		if (ret)
+		if (ret) {
+			i915_gem_object_unpin_pages(obj);
 			return ret;
+		}
 
 		goto search_free;
 	}
 	if (WARN_ON(!i915_gem_valid_gtt_space(dev,
 					      obj->gtt_space,
 					      obj->cache_level))) {
+		i915_gem_object_unpin_pages(obj);
 		drm_mm_put_block(obj->gtt_space);
 		obj->gtt_space = NULL;
 		return -EINVAL;
@@ -2971,6 +2976,7 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 
 	ret = i915_gem_gtt_prepare_object(obj);
 	if (ret) {
+		i915_gem_object_unpin_pages(obj);
 		drm_mm_put_block(obj->gtt_space);
 		obj->gtt_space = NULL;
 		return ret;
@@ -2993,6 +2999,7 @@ i915_gem_object_bind_to_gtt(struct drm_i915_gem_object *obj,
 
 	obj->map_and_fenceable = mappable && fenceable;
 
+	i915_gem_object_unpin_pages(obj);
 	trace_i915_gem_object_bind(obj, map_and_fenceable);
 	i915_gem_verify_gtt(dev);
 	return 0;