linux-kernel - Re: [PATCH] staging: sound: Adjust mutex unlock order

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Message-ID: <87tt3c8wye.wl-tiwai@suse.de>
Date: Wed, 16 Jul 2025 08:35:21 +0200
From: Takashi Iwai <tiwai@...e.de>
To: Erick Karanja <karanja99erick@...il.com>
Cc: perex@...ex.cz,
	tiwai@...e.com,
	linux-sound@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	julia.lawall@...ia.fr
Subject: Re: [PATCH] staging: sound: Adjust mutex unlock order

On Wed, 16 Jul 2025 08:23:30 +0200,
Erick Karanja wrote:
> 
> The mutexes qdev_mutex and chip->mutex are acquired in that order
> throughout the driver. To preserve proper lock hierarchy and avoid
> potential deadlocks, they must be released in the reverse order
> of acquisition.
> 
> This change reorders the unlock sequence to first release chip->mutex
> followed by qdev_mutex, ensuring consistency with the locking pattern.
> 
> Signed-off-by: Erick Karanja <karanja99erick@...il.com>
> ---
>  sound/usb/qcom/qc_audio_offload.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
> index 3543b5a53592..ef144d2be7d2 100644
> --- a/sound/usb/qcom/qc_audio_offload.c
> +++ b/sound/usb/qcom/qc_audio_offload.c
> @@ -825,8 +825,8 @@ static int uaudio_sideband_notifier(struct usb_interface *intf,
>  		}
>  	}
>  
> -	mutex_unlock(&qdev_mutex);
>  	mutex_unlock(&chip->mutex);
> +	mutex_unlock(&qdev_mutex);
>  
>  	return 0;
>  }

The same pattern is found in qc_usb_audio_offload_disconnect() and
qc_usb_audio_offload_suspend(), too.
Care to address there as well?

Maybe it's better to replace with guard stuff, but it should be done
by another patch in later kernel releases.


thanks,

Takashi