linux-kernel - Re: [greybus-dev] [PATCH] staging: greybus: Add missing rwsem around snd_ctl

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Message-ID: <s5h5ysqlcm8.wl-tiwai@suse.de>
Date:   Wed, 17 Nov 2021 22:02:23 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Alex Elder <elder@...aro.org>
Cc:     Takashi Iwai <tiwai@...e.de>, greybus-dev@...ts.linaro.org,
        Alex Elder <elder@...nel.org>, Johan Hovold <johan@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [greybus-dev] [PATCH] staging: greybus: Add missing rwsem around snd_ctl_remove() calls

On Wed, 17 Nov 2021 20:56:14 +0100,
Alex Elder wrote:
> 
> On 11/16/21 1:20 AM, Takashi Iwai wrote:
> > snd_ctl_remove() has to be called with card->controls_rwsem held (when
> > called after the card instantiation).  This patch adds the missing
> > rwsem calls around it.
> 
> I see the comment above snd_ctl_remove() that says you must hold
> the write lock.  And given that, this seems correct to me.
> 
> I understand why you want to take the lock just once, rather
> than each time snd_ctl_remove() is called.
> 
> However I believe the acquisition and release of the lock
> belongs inside gbaudio_remove_controls(), not in its caller.
> 
> If you disagree, can you please explain why?

In general if the function returns an error and has a loop inside,
taking a lock in the caller side avoids the forgotten unlock.


Takashi


> Otherwise, will you please submit version two, taking the
> lock inside gbaudio_remove_controls()?
> 
> Thanks.
> 
> 					-Alex
> 
> > Fixes: 510e340efe0c ("staging: greybus: audio: Add helper APIs for dynamic audio modules")
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > ---
> >   drivers/staging/greybus/audio_helper.c | 8 ++++++--
> >   1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/staging/greybus/audio_helper.c b/drivers/staging/greybus/audio_helper.c
> > index 1ed4772d2771..843760675876 100644
> > --- a/drivers/staging/greybus/audio_helper.c
> > +++ b/drivers/staging/greybus/audio_helper.c
> > @@ -192,7 +192,11 @@ int gbaudio_remove_component_controls(struct snd_soc_component *component,
> >   				      unsigned int num_controls)
> >   {
> >   	struct snd_card *card = component->card->snd_card;
> > +	int err;
> >   -	return gbaudio_remove_controls(card, component->dev, controls,
> > -				       num_controls, component->name_prefix);
> > +	down_write(&card->controls_rwsem);
> > +	err = gbaudio_remove_controls(card, component->dev, controls,
> > +				      num_controls, component->name_prefix);
> > +	up_write(&card->controls_rwsem);
> > +	return err;
> >   }
> >
>