[bug report] md: also clone new io if io accounting is disabled

[Dan Carpenter <dan.carpenter@xxxxxxxxxx>]

Hello Yu Kuai,

The patch c687297b8845: "md: also clone new io if io accounting is
disabled" from Jun 22, 2023 (linux-next), leads to the following
Smatch static checker warning:

	drivers/md/md.c:8718 md_clone_bio()
	potential NULL container_of 'clone'

drivers/md/md.c
    8711 static void md_clone_bio(struct mddev *mddev, struct bio **bio)
    8712 {
    8713         struct block_device *bdev = (*bio)->bi_bdev;
    8714         struct md_io_clone *md_io_clone;
    8715         struct bio *clone =
    8716                 bio_alloc_clone(bdev, *bio, GFP_NOIO, &mddev->io_clone_set);

Generally in the kernel, you have to check for allocation failure.  In
this case if the allocation fails it leads to a NULL dereference.

    8717 
--> 8718         md_io_clone = container_of(clone, struct md_io_clone, bio_clone);
    8719         md_io_clone->orig_bio = *bio;
    8720         md_io_clone->mddev = mddev;
    8721         if (blk_queue_io_stat(bdev->bd_disk->queue))
    8722                 md_io_clone->start_time = bio_start_io_acct(*bio);
    8723 
    8724         clone->bi_end_io = md_end_clone_io;
    8725         clone->bi_private = md_io_clone;
    8726         *bio = clone;
    8727 }

regards,
dan carpenter