Re: [PATCH v2] ublk: stop reporting zones on an empty response

[Ming Lei]

On Tue, Nov 10, 2026 at 9:15 PM <shao.mingyin@xxxxxxxxxx> wrote:
>
> From: Shao Mingyin <shao.mingyin@xxxxxxxxxx>
>
> ublk_report_zones() treats a zero-length zone as the end of the current
> server response and keeps asking for the remaining zones from the sector
> after the last reported one.  A response that carries no zone at all
> therefore advances neither done_zones nor sector, and the driver issues
> REPORT ZONES requests for the same sector forever.  Both BLKREPORTZONE
> and the zone revalidation done when the device starts hang, and the task
> cannot be killed.
>
> Only a response with no zone cannot make progress.  Terminate the whole
> report in that case, and keep following up on a short but non-empty
> response as before, which is what sd_zbc and virtio_blk do.
>
> Fixes: 29802d7ca33b ("ublk: enable zoned storage support")
> Suggested-by: Ming Lei <tom.leiming@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Shao Mingyin <shao.mingyin@xxxxxxxxxx>
> ---
> v2:
> - Stop only when a response carries no zone at all, so that a short but
>   non-empty response is still followed up from the advanced sector.
>   The v1 form ended the whole report at the first zero-length zone and
>   truncated such reports (reported by Ming Lei).
> v1: https://lore.kernel.org/all/20261109225110056QQJAEflTHzwYHzwXlMBb_@xxxxxxxxxx/
>
>  drivers/block/ublk_drv.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -661,6 +661,7 @@ static int ublk_report_zones(struct gendisk *disk, sector_t sector,
>                 struct request *req;
>                 struct ublk_zoned_report_desc desc;
>                 blk_status_t status;
> +               unsigned int i;
>
>                 memset(buffer, 0, buffer_length);
>
> @@ -689,7 +690,7 @@ static int ublk_report_zones(struct gendisk *disk, sector_t sector,
>                 if (ret)
>                         goto out;
>
> -               for (unsigned int i = 0; i < zones_in_request; i++) {
> +               for (i = 0; i < zones_in_request; i++) {
>                         struct blk_zone *zone = buffer + i;
>
>                         /* A zero length zone means no more zones in this response */
> @@ -704,6 +705,10 @@ static int ublk_report_zones(struct gendisk *disk, sector_t sector,
>                         sector += zone_size_sectors;
>
>                 }
> +
> +               /* An empty response cannot make progress, stop asking. */
> +               if (!i)
> +                       break;
>         }

Looks fine, and verified with one ublk zoned server which returns
empty or short report: BLKREPORTZONE & START_DEV don't hang any more
on empty response, and all zones are still reported on short response.

Reviewed-by: Ming Lei <tom.leiming@xxxxxxxxx>


Thanks,
Ming Lei