Re: [PATCH v13 13/25] v4l: async: Allow async notifier register call succeed with no subdevs

[Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>]

Hi Sakari,

On Tuesday, 19 September 2017 15:04:43 EEST Laurent Pinchart wrote:
> Hi Sakari,
> 
> Thank you for the patch.
> 
> On Friday, 15 September 2017 17:17:12 EEST Sakari Ailus wrote:
> > The information on how many async sub-devices would be bindable to a
> > notifier is typically dependent on information from platform firmware and
> > it's not driver's business to be aware of that.
> > 
> > Many V4L2 main drivers are perfectly usable (and useful) without async
> > sub-devices and so if there aren't any around, just proceed call the
> > notifier's complete callback immediately without registering the notifier
> > itself.
> > 
> > If a driver needs to check whether there are async sub-devices available,
> > it can be done by inspecting the notifier's num_subdevs field which tells
> > the number of async sub-devices.
> > 
> > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> 
> Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>

I take this back.

> > ---
> > 
> >  drivers/media/v4l2-core/v4l2-async.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/media/v4l2-core/v4l2-async.c
> > b/drivers/media/v4l2-core/v4l2-async.c index 9895b610e2a0..4be2f16af051
> > 100644
> > --- a/drivers/media/v4l2-core/v4l2-async.c
> > +++ b/drivers/media/v4l2-core/v4l2-async.c
> > @@ -170,14 +170,16 @@ int v4l2_async_notifier_register(struct v4l2_device
> > *v4l2_dev, struct v4l2_async_subdev *asd;
> > 
> >  	int i;
> > 
> > -	if (!v4l2_dev || !notifier->num_subdevs ||
> > -	    notifier->num_subdevs > V4L2_MAX_SUBDEVS)
> > +	if (!v4l2_dev || notifier->num_subdevs > V4L2_MAX_SUBDEVS)
> > 
> >  		return -EINVAL;
> >  	
> >  	notifier->v4l2_dev = v4l2_dev;
> >  	INIT_LIST_HEAD(&notifier->waiting);
> >  	INIT_LIST_HEAD(&notifier->done);
> > 
> > +	if (!notifier->num_subdevs)
> > +		return v4l2_async_notifier_call_complete(notifier);
> > +

This skips adding the notifier to the notifier_list. Won't this result in an 
oops when calling list_del(&notifier->list) in 
v4l2_async_notifier_unregister() ?

> >  	for (i = 0; i < notifier->num_subdevs; i++) {
> >  	
> >  		asd = notifier->subdevs[i];

-- 
Regards,

Laurent Pinchart