drm/msm: Init mm_list before accessing it for use_vram path

Fix NULL pointer dereference caused by update_inactive()
trying to list_del() an uninitialized mm_list who's
prev/next pointers are NULL.

Fixes: 64fcbde7 ("drm/msm: Track potentially evictable objects")
Signed-off-by: Alexey Minnekhanov <alexeymin@postmarketos.org>
Link: https://lore.kernel.org/r/20210518102624.1193955-1-alexeymin@postmarketos.orgSigned-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/msm_gem.c

@@ -1241,6 +1241,13 @@ static struct drm_gem_object *_msm_gem_new(struct drm_device *dev,
 
 		to_msm_bo(obj)->vram_node = &vma->node;
 
+		/* Call chain get_pages() -> update_inactive() tries to
+		 * access msm_obj->mm_list, but it is not initialized yet.
+		 * To avoid NULL pointer dereference error, initialize
+		 * mm_list to be empty.
+		 */
+		INIT_LIST_HEAD(&msm_obj->mm_list);
+
 		msm_gem_lock(obj);
 		pages = get_pages(obj);
 		msm_gem_unlock(obj);