Re: [RFC PATCH 10/14] sound: usb: card: Check for support for requested audio format

Greg KH
2022-12-24T08:59:13Z

On Fri, Dec 23, 2022 at 03:31:56PM -0800, Wesley Cheng wrote:
> Allow for checks on a specific USB audio device to see if a requested PCM
> format is supported. This is needed for support for when playback is
> initiated by the ASoC USB backend path.
>
> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> ---
> sound/usb/card.c | 19 +++++++++++++++++++
> sound/usb/card.h | 3 +++
> 2 files changed, 22 insertions(+)
>
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 396e5a34e23b..9b8d2ed308c8 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -133,6 +133,25 @@ int snd_usb_unregister_vendor_ops(void)
> }
> EXPORT_SYMBOL_GPL(snd_usb_unregister_vendor_ops);
>
> +struct snd_usb_stream *snd_usb_find_suppported_substream(int card_idx,
> + struct snd_pcm_hw_params *params, int direction)
> +{
> + struct snd_usb_stream *as;
> + struct snd_usb_substream *subs = NULL;
> + const struct audioformat *fmt;
> +
> + if (usb_chip[card_idx] && enable[card_idx]) {
> + list_for_each_entry(as, &usb_chip[card_idx]->pcm_list, list) {
> + subs = &as->substream[direction];
> + fmt = find_substream_format(subs, params);
> + if (fmt)
> + return as;
> + }
> + }

Where is the locking here? How can you walk a list that can be changed
as you walk it?

And what about reference counting? You are returning a pointer to a
structure, who now "owns" it? What happens if it is removed from the
system after you return it?

> + return 0;

Didn't sparse complain about this? You can't return "0" as a pointer,
it should be NULL.

Always run basic tools like sparse on code before submitting it so that
we don't have to find errors like this.

thanks,

greg k-h