On Mon, Jan 04, 2021 at 10:06:59PM +0900, Minwoo Im wrote:

+	if (q->backing_dev_info && q->backing_dev_info->owner &&
+			limits->logical_block_size != size) {
+		bdev = blkdev_get_no_open(q->backing_dev_info->owner->devt);
+		bdev->bd_disk->flags |= GENHD_FL_BLOCK_SIZE_CHANGED;
+		blkdev_put_no_open(bdev);
+	}

We really need the backpointer from the queue to the gendisk I've wanted
to add for a while.  Can we at least restrict this to a live gendisk?

Also I think the size change flag should go into the ->state field and
use the atomic bitops helpers to avoid concurrency problems.