drm/i915: Assert the drm_mm_node is allocated when on the VM lists

Before moving the vma between the VM active/inactive lists, assert that
the node is still allocated.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/20170119192659.31789-5-chris@chris-wilson.co.ukReviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -702,6 +702,8 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_i915_private *dev_priv
 		goto err_pages;
 	}
 
+	GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
+
 	vma->pages = obj->mm.pages;
 	vma->flags |= I915_VMA_GLOBAL_BIND;
 	__i915_vma_set_map_and_fenceable(vma);

drivers/gpu/drm/i915/i915_vma.c

@@ -45,6 +45,7 @@ i915_vma_retire(struct i915_gem_active *active,
 	if (i915_vma_is_active(vma))
 		return;
 
+	GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
 	list_move_tail(&vma->vm_link, &vma->vm->inactive_list);
 	if (unlikely(i915_vma_is_closed(vma) && !i915_vma_is_pinned(vma)))
 		WARN_ON(i915_vma_unbind(vma));
@@ -493,6 +494,7 @@ i915_vma_insert(struct i915_vma *vma, u64 size, u64 alignment, u64 flags)
 		GEM_BUG_ON(vma->node.start < start);
 		GEM_BUG_ON(vma->node.start + vma->node.size > end);
 	}
+	GEM_BUG_ON(!drm_mm_node_allocated(&vma->node));
 	GEM_BUG_ON(!i915_gem_valid_gtt_space(vma, obj->cache_level));
 
 	list_move_tail(&obj->global_link, &dev_priv->mm.bound_list);