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

[Caleb Sander Mateos]

On Fri, Aug 8, 2025 at 2:01 PM Uday Shankar <ushankar@xxxxxxxxxxxxxxx> wrote:
>
> 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@xxxxxxxxxxxxxxx>
> > 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);

I was trying to avoid the capable() call if unprivileged_daemons was
already set. But maybe that's not a common case and it's not worth
optimizing?

Best,
Caleb

>
> >
> >       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
> >