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

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Message-ID: <4a7f48ff7c3a93afe4ec3847addaedf75f95ac03.camel@gmail.com>
Date: Wed, 16 Jul 2025 09:39:34 +0300
From: Erick Karanja <karanja99erick@...il.com>
To: Takashi Iwai <tiwai@...e.de>
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, 2025-07-16 at 08:35 +0200, Takashi Iwai wrote:
> 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?
Yes, working on it.
> 
> Maybe it's better to replace with guard stuff, but it should be done
> by another patch in later kernel releases.
> 
> 
> thanks,
> 
> Takashi