On Wed, 27 Nov 2024 at 10:12, Laurent Pinchart
<laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Wed, Nov 27, 2024 at 07:46:10AM +0000, Ricardo Ribalda wrote:
> > If a file handle is waiting for a response from an async control, avoid
> > that other file handle operate with it.
> >
> > Without this patch, the first file handle will never get the event
> > associated to that operation.
>
> Please explain why that is an issue (both for the commit message and for
> me, as I'm not sure what you're fixing here).
What about something like this:
Without this patch, the first file handle will never get the event
associated with that operation, which can lead to endless loops in
applications. Eg:
If an application A wants to change the zoom and to know when the
operation has completed:
it will open the video node, subscribe to the zoom event, change the
control and wait for zoom to finish.
If before the zoom operation finishes, another application B changes
the zoom, the first app A will loop forever.
>
> What may be an issue is that ctrl->handle seem to be accessed from
> different contexts without proper locking :-S
Isn't it always protected by ctrl_mutex?
>
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
> > Signed-off-by: Ricardo Ribalda <ribalda@xxxxxxxxxxxx>
> > ---
> > drivers/media/usb/uvc/uvc_ctrl.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> > index 4fe26e82e3d1..5d3a28edf7f0 100644
> > --- a/drivers/media/usb/uvc/uvc_ctrl.c
> > +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> > @@ -1950,6 +1950,10 @@ int uvc_ctrl_set(struct uvc_fh *handle,
> > if (!(ctrl->info.flags & UVC_CTRL_FLAG_SET_CUR))
> > return -EACCES;
> >
> > + /* Other file handle is waiting a response from this async control. */
> > + if (ctrl->handle && ctrl->handle != handle)
> > + return -EBUSY;
> > +
> > /* Clamp out of range values. */
> > switch (mapping->v4l2_type) {
> > case V4L2_CTRL_TYPE_INTEGER:
>
> --
> Regards,
>
> Laurent Pinchart
--
Ricardo Ribalda
