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

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Message-ID: <CANiDSCunwy4wYL3-J5KNp4cG4mGsq8FtoyJ6hOr3VK+9+L2LgA@mail.gmail.com>
Date:   Wed, 22 Nov 2023 08:35:24 +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 08:21, 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


>
> >       uvc_input_unregister(dev);
> >  }



-- 
Ricardo Ribalda