Re: [PATCH] virtio-blk: avoid kernel panic on VIRTIO_BLK_F_ZONED check

[Lorenzo Stoakes <lstoakes@gmail.com>]

On Wed, Dec 21, 2022 at 02:00:12PM +0000, Lorenzo Stoakes wrote:
> virtio zoned block device support is added by commit 0562d7bf1604
> ("virtio-blk: add support for zoned block devices") which adds
> VIRTIO_BLK_F_ZONED to the features array in virtio_blk.c but makes it
> conditional on CONFIG_BLK_DEV_ZONED.
>
> In it virtblk_probe() calls virtio_has_feature(vdev, VIRTIO_BLK_F_ZONED)
> unconditionally, which invokes virtio_check_driver_offered_feature().
> This function checks whether virtio_blk.feature_table (assigned to
> the static features array) contains the specified feature enum, and if not
> _causes a kernel panic_ via BUG().
>
> This therefore means that failing to enable CONFIG_BLK_DEV_ZONED while
> using virtio is a guaranteed kernel panic. Fix the issue by making the
> feature test also conditional on CONFIG_BLK_DEV_ZONED.
>
> Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
> ---
>  drivers/block/virtio_blk.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index ff49052e26f7..34fdc141fb21 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -1580,11 +1580,13 @@ static int virtblk_probe(struct virtio_device *vdev)
>  	virtblk_update_capacity(vblk, false);
>  	virtio_device_ready(vdev);
>
> +#ifdef CONFIG_BLK_DEV_ZONED
>  	if (virtio_has_feature(vdev, VIRTIO_BLK_F_ZONED)) {
>  		err = virtblk_probe_zoned_device(vdev, vblk, q);
>  		if (err)
>  			goto out_cleanup_disk;
>  	}
> +#endif /* CONFIG_BLK_DEV_ZONED */
>
>  	dev_info(&vdev->dev, "blk config size: %zu\n",
>  		sizeof(struct virtio_blk_config));
> --
> 2.39.0

Steven suggested use of IS_ENABLED() here which makes it rather less ugly, will
send as a v2.