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

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Date:   Wed, 17 Nov 2021 13:56:14 -0600
From:   Alex Elder <elder@...aro.org>
To:     Takashi Iwai <tiwai@...e.de>, greybus-dev@...ts.linaro.org
Cc:     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 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?

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;
>   }
>