Re: [RFC PATCH v2 12/22] sound: usb: card: Introduce USB SND platform op callbacks

[Wesley Cheng]

Hi Pierre,

On 1/26/2023 7:50 AM, Pierre-Louis Bossart wrote:
> > +int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
> > +{
> > +	if (platform_ops)
> > +		return -EEXIST;
> > +
> > +	platform_ops = ops;
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(snd_usb_register_platform_ops);
> > +
> > +int snd_usb_unregister_platform_ops(void)
> > +{
> > +	platform_ops = NULL;
> > +	return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(snd_usb_unregister_platform_ops);
>
> I find this super-racy.
>
> If the this function is called just before ...
>
> >   
> >   /*
> >    * disconnect streams
> > @@ -910,6 +928,10 @@ static int usb_audio_probe(struct usb_interface *intf,
> >   	usb_set_intfdata(intf, chip);
> >   	atomic_dec(&chip->active);
> >   	mutex_unlock(&register_mutex);
> > +
> > +	if (platform_ops->connect_cb)
> > +		platform_ops->connect_cb(intf, chip);
> > +
>
> ... this, then you have a risk of using a dandling pointer.
>
> You also didn't test that the platform_ops != NULL, so there's a risk of
> dereferencing a NULL pointer.
>
> Not so good, eh?
>
> It's a classic (I've had the same sort of issues with SoundWire), when
> you export ops from one driver than can be removed, then additional
> protection is needed when using those callbacks.

Yep, will take a look at this a bit more to improve it.

Thanks
Wesley Cheng