bdi mishandling patch

diff -u a/block/blk-core.c b/block/blk-core.c
--- a/block/blk-core.c      2017-02-26 05:08:29.000000000 -0500
+++ b/block/blk-core.c      2018-12-06 11:54:54.109695294 -0500
@@ -595,8 +595,6 @@
                q->queue_lock = &q->__queue_lock;
        spin_unlock_irq(lock);

-       bdi_unregister(&q->backing_dev_info);
-
        /* @q is and will stay empty, shutdown and put */
        blk_put_queue(q);
 }
diff -u a/block/genhd.c b/block/genhd.c
--- a/block/genhd.c 2017-02-26 05:08:29.000000000 -0500
+++ b/block/genhd.c 2018-12-06 17:53:00.777695294 -0500
@@ -656,7 +656,16 @@
        disk->flags &= ~GENHD_FL_UP;

        sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
-       blk_unregister_queue(disk);
+       if (disk->queue) {
+               /*
+                * Unregister bdi before releasing device numbers (as they can
+                * get reused and we'd get clashes in sysfs).
+                */
+               bdi_unregister(&disk->queue->backing_dev_info);
+               blk_unregister_queue(disk);
+       } else {
+               WARN_ON(1);
+       }
        blk_unregister_region(disk_devt(disk), disk->minors);

        part_stat_set_all(&disk->part0, 0);