Date:   Thu, 9 Mar 2023 07:44:13 +0100
From:   Greg KH <gregkh@linuxfoundation.org>
To:     Wesley Cheng <quic_wcheng@quicinc.com>
Cc:     srinivas.kandagatla@linaro.org, mathias.nyman@intel.com,
        perex@perex.cz, broonie@kernel.org, lgirdwood@gmail.com,
        krzysztof.kozlowski+dt@linaro.org, agross@kernel.org,
        Thinh.Nguyen@synopsys.com, bgoswami@quicinc.com,
        andersson@kernel.org, robh+dt@kernel.org, tiwai@suse.com,
        linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        alsa-devel@alsa-project.org, devicetree@vger.kernel.org,
        linux-usb@vger.kernel.org, quic_jackp@quicinc.com,
        quic_plai@quicinc.com
Subject: Re: [PATCH v3 09/28] sound: usb: card: Introduce USB SND platform op
 callbacks
Message-ID: <ZAmAPX6Q1m0HU/Qo@kroah.com>
References: <20230308235751.495-1-quic_wcheng@quicinc.com>
 <20230308235751.495-10-quic_wcheng@quicinc.com>
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In-Reply-To: <20230308235751.495-10-quic_wcheng@quicinc.com>
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On Wed, Mar 08, 2023 at 03:57:32PM -0800, Wesley Cheng wrote:
> Allow for different platforms to be notified on USB SND connect/disconnect
> seqeunces.  This allows for platform USB SND modules to properly initialize
> and populate internal structures with references to the USB SND chip
> device.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
> ---
>  sound/usb/card.c | 36 ++++++++++++++++++++++++++++++++++++
>  sound/usb/card.h | 20 ++++++++++++++++++++
>  2 files changed, 56 insertions(+)
> 
> diff --git a/sound/usb/card.c b/sound/usb/card.c
> index 26268ffb8274..9bcbaa0c0a55 100644
> --- a/sound/usb/card.c
> +++ b/sound/usb/card.c
> @@ -117,6 +117,30 @@ MODULE_PARM_DESC(skip_validation, "Skip unit descriptor validation (default: no)
>  static DEFINE_MUTEX(register_mutex);
>  static struct snd_usb_audio *usb_chip[SNDRV_CARDS];
>  static struct usb_driver usb_audio_driver;
> +static struct snd_usb_platform_ops *platform_ops;

As I've said before, you can not just have one of these.  They need to
be per-bus structure.  Or per-device, something dynamic, not static like
this.

> +int snd_usb_register_platform_ops(struct snd_usb_platform_ops *ops)
> +{
> +	if (platform_ops)
> +		return -EEXIST;
> +
> +	mutex_lock(&register_mutex);
> +	platform_ops = ops;
> +	mutex_unlock(&register_mutex);

Your locking is odd for a single pointer, why is it needed at all?

Also you check the pointer before using the lock, which defeats the lock
in the first place.

thanks,

greg k-h