linux-kernel - Re: [PATCH v3 1/3] media: uvcvideo: Always use uvc_status

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Message-ID: <CANiDSCs9BZWOjDM6fxz-ipXqDAm9==aRw9giKRnk1XXyc1J35A@mail.gmail.com>
Date:   Wed, 22 Nov 2023 10:53:53 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Tomasz Figa <tfiga@...omium.org>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Alan Stern <stern@...land.harvard.edu>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Sean Paul <seanpaul@...omium.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>
Subject: Re: [PATCH v3 1/3] media: uvcvideo: Always use uvc_status_stop()

Hi Sergey

On Wed, 22 Nov 2023 at 08:35, Ricardo Ribalda <ribalda@...omium.org> wrote:
>
> Hi Sergey
>
> On Wed, 22 Nov 2023 at 08:21, Sergey Senozhatsky
> <senozhatsky@...omium.org> wrote:
> >
> > On (23/11/21 19:53), Ricardo Ribalda wrote:
> > > uvc_status_stop() handles properly the race conditions with the
> > > asynchronous worker.
> > > Let's use uvc_status_stop() for all the code paths that require stopping
> > > it.
> > >
> > > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> > > ---
> > >  drivers/media/usb/uvc/uvc_ctrl.c   | 4 ----
> > >  drivers/media/usb/uvc/uvc_status.c | 2 +-
> > >  2 files changed, 1 insertion(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > > index e59a463c2761..8e22a07e3e7b 100644
> > > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > > @@ -2765,10 +2765,6 @@ void uvc_ctrl_cleanup_device(struct uvc_device *dev)
> > >       struct uvc_entity *entity;
> > >       unsigned int i;
> > >
> > > -     /* Can be uninitialized if we are aborting on probe error. */
> > > -     if (dev->async_ctrl.work.func)
> > > -             cancel_work_sync(&dev->async_ctrl.work);
> > > -
> > >       /* Free controls and control mappings for all entities. */
> > >       list_for_each_entry(entity, &dev->entities, list) {
> > >               for (i = 0; i < entity->ncontrols; ++i) {
> > > diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> > > index a78a88c710e2..0208612a9f12 100644
> > > --- a/drivers/media/usb/uvc/uvc_status.c
> > > +++ b/drivers/media/usb/uvc/uvc_status.c
> > > @@ -292,7 +292,7 @@ int uvc_status_init(struct uvc_device *dev)
> > >
> > >  void uvc_status_unregister(struct uvc_device *dev)
> > >  {
> > > -     usb_kill_urb(dev->int_urb);
> > > +     uvc_status_stop(dev);
> >
> > Sort of feels like this needs dev->lock somewhere here. Should we move 3/3
> > to the head of the series?
> >
> > The question is, can this be called in parallel with uvc_v4l2_release(),
> > for instance?
>
> I can be called in parallel with uvc_v4l2_release(), but
> uvc_status_stop() is thread-safe and does not take any locks after:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=619d9b710cf06f7a00a17120ca92333684ac45a8
>
> So this "should" be good. key-word here is should :P

To be on the safe side I am not going to run the async work on the
release path. will send a new revision

>
>
> >
> > >       uvc_input_unregister(dev);
> > >  }
>
>
>
> --
> Ricardo Ribalda



-- 
Ricardo Ribalda