Re: [PATCH] ublk: check for unprivileged daemon on each I/O fetch

[Uday Shankar <ushankar@purestorage.com>]

On Fri, Aug 08, 2025 at 09:52:15AM -0600, Caleb Sander Mateos wrote:
> Commit ab03a61c6614 ("ublk: have a per-io daemon instead of a per-queue
> daemon") allowed each ublk I/O to have an independent daemon task.
> However, nr_privileged_daemon is only computed based on whether the last
> I/O fetched in each ublk queue has an unprivileged daemon task.
> Fix this by checking whether every fetched I/O's daemon is privileged.
> Change nr_privileged_daemon from a count of queues to a boolean
> indicating whether any I/Os have an unprivileged daemon.
> 
> Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
> Fixes: ab03a61c6614 ("ublk: have a per-io daemon instead of a per-queue daemon")

Nice catch!

> ---
>  drivers/block/ublk_drv.c | 16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/block/ublk_drv.c b/drivers/block/ublk_drv.c
> index 6561d2a561fa..a035070dd690 100644
> --- a/drivers/block/ublk_drv.c
> +++ b/drivers/block/ublk_drv.c
> @@ -233,11 +233,11 @@ struct ublk_device {
>  
>  	struct ublk_params	params;
>  
>  	struct completion	completion;
>  	unsigned int		nr_queues_ready;
> -	unsigned int		nr_privileged_daemon;
> +	bool 			unprivileged_daemons;
>  	struct mutex cancel_mutex;
>  	bool canceling;
>  	pid_t 	ublksrv_tgid;
>  };
>  
> @@ -1548,11 +1548,11 @@ static void ublk_reset_ch_dev(struct ublk_device *ub)
>  		ublk_queue_reinit(ub, ublk_get_queue(ub, i));
>  
>  	/* set to NULL, otherwise new tasks cannot mmap io_cmd_buf */
>  	ub->mm = NULL;
>  	ub->nr_queues_ready = 0;
> -	ub->nr_privileged_daemon = 0;
> +	ub->unprivileged_daemons = false;
>  	ub->ublksrv_tgid = -1;
>  }
>  
>  static struct gendisk *ublk_get_disk(struct ublk_device *ub)
>  {
> @@ -1978,16 +1978,14 @@ static void ublk_reset_io_flags(struct ublk_device *ub)
>  /* device can only be started after all IOs are ready */
>  static void ublk_mark_io_ready(struct ublk_device *ub, struct ublk_queue *ubq)
>  	__must_hold(&ub->mutex)
>  {
>  	ubq->nr_io_ready++;
> -	if (ublk_queue_ready(ubq)) {
> +	if (ublk_queue_ready(ubq))
>  		ub->nr_queues_ready++;
> -
> -		if (capable(CAP_SYS_ADMIN))
> -			ub->nr_privileged_daemon++;
> -	}
> +	if (!ub->unprivileged_daemons && !capable(CAP_SYS_ADMIN))
> +		ub->unprivileged_daemons = true;

Shorter:

ub->unprivileged_daemons |= !capable(CAP_SYS_ADMIN);

>  
>  	if (ub->nr_queues_ready == ub->dev_info.nr_hw_queues) {
>  		/* now we are ready for handling ublk io request */
>  		ublk_reset_io_flags(ub);
>  		complete_all(&ub->completion);
> @@ -2878,12 +2876,12 @@ static int ublk_ctrl_start_dev(struct ublk_device *ub,
>  	ub->dev_info.ublksrv_pid = ublksrv_pid;
>  	ub->ub_disk = disk;
>  
>  	ublk_apply_params(ub);
>  
> -	/* don't probe partitions if any one ubq daemon is un-trusted */
> -	if (ub->nr_privileged_daemon != ub->nr_queues_ready)
> +	/* don't probe partitions if any daemon task is un-trusted */
> +	if (ub->unprivileged_daemons)
>  		set_bit(GD_SUPPRESS_PART_SCAN, &disk->state);
>  
>  	ublk_get_device(ub);
>  	ub->dev_info.state = UBLK_S_DEV_LIVE;
>  
> -- 
> 2.45.2
>