Re: [PATCH 8/8] scsi: Introduce ZBC disk I/O scheduler

[Bart Van Assche]

On Fri, 2017-09-01 at 20:36 +0900, Damien Le Moal wrote:
> +static struct scsi_disk *__zoned_scsi_disk(struct request_queue *q)
> +{
> +       struct scsi_device *sdp;
> +       struct scsi_disk *sdkp;
> +
> +       if (!blk_queue_is_zoned(q)) {
> +               pr_err("zoned: Not a zoned block device\n");
> +               return NULL;
> +       }
> +
> +       sdp = scsi_device_from_queue(q);
> +       if (!sdp) {
> +               pr_err("zoned: Not a SCSI device\n");
> +               return NULL;
> +       }
> +
> +       sdkp = dev_get_drvdata(&sdp->sdev_gendev);
> +       if (WARN_ON(sdkp->disk->queue != q))
> +               return NULL;
> +
> +       return sdkp;
> +}

Hello Damien,

Can reading sdkp->disk->queue cause a kernel crash if sdp does not point at
a SCSI device that is associated with a SCSI disk? How about using something
like the code below to convert a request queue pointer into a SCSI disk
pointer?

static int lookup_disk(struct device *dev, void *data)
{
        struct scsi_disk **sdkp = data;

        if (!*sdkp && dev->class == &sd_disk_class)
                *sdkp = to_scsi_disk(dev);

        return 0;
}

static struct scsi_disk *q_to_sdkp(struct request_queue *q)
{
        struct scsi_device *sdp = scsi_device_from_queue(q);
        struct scsi_disk *sdkp = NULL;

        if (sdp)
                device_for_each_child(&sdp->sdev_gendev, &sdkp, lookup_disk);
        return sdkp;
}

Thanks,

Bart.