linux-kernel - Re: [PATCH v1] iio: mtk-auxadc: add mutex

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Date:   Fri, 30 Jul 2021 14:44:39 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Hui Liu <hui.liu@...iatek.com>
CC:     <robh+dt@...nel.org>, <jic23@...nel.org>, <lars@...afoo.de>,
        <pmeerw@...erw.net>, <srv_heupstream@...iatek.com>,
        <zhiyong.tao@...iatek.com>, <chun-hung.wu@...iatek.com>,
        <yingjoe.chen@...iatek.com>, <seiya.wang@...iatek.com>,
        <matthias.bgg@...il.com>, <s.hauer@...gutronix.de>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-iio@...r.kernel.org>, <linux-mediatek@...ts.infradead.org>
Subject: Re: [PATCH v1] iio: mtk-auxadc: add mutex_destroy

On Thu, 29 Jul 2021 16:01:35 +0800
Hui Liu <hui.liu@...iatek.com> wrote:

> Add mutex_destroy when probe fail and remove device.
> 
> Signed-off-by: Hui Liu <hui.liu@...iatek.com>

Hi Hui Liu,

Two things here.

1) You need to explain with a clear example flow when this would serve a
   useful purpose.  As I explained before, we do no in general put mutex_destroy()
   in remove paths as it is usually just noise.

2) It's in the wrong order logically. mutex init is between the clk_prepare_enable
   and iio_device_register, hence if we are going to have mutex destroy it must also
   be in that that location (remove should be reverse of probe or there should be
   a clear comment explaining why we need to do things in a different order.

3) If touching this code at all, please move all of the probe / remove to devm_
   managed code so that we don't need to get this ordering right at all because
   it will be done automatically.

So I won't apply this without 1 and even if I accepted the principle, it's
still in the wrong place in remove.

Jonathan

> ---
>  drivers/iio/adc/mt6577_auxadc.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iio/adc/mt6577_auxadc.c b/drivers/iio/adc/mt6577_auxadc.c
> index 79c1dd68b909..d57243037ad6 100644
> --- a/drivers/iio/adc/mt6577_auxadc.c
> +++ b/drivers/iio/adc/mt6577_auxadc.c
> @@ -289,6 +289,7 @@ static int mt6577_auxadc_probe(struct platform_device *pdev)
>  	ret = iio_device_register(indio_dev);
>  	if (ret < 0) {
>  		dev_err(&pdev->dev, "failed to register iio device\n");
> +		mutex_destroy(&adc_dev->lock);
>  		goto err_power_off;
>  	}
>  
> @@ -313,6 +314,7 @@ static int mt6577_auxadc_remove(struct platform_device *pdev)
>  			      0, MT6577_AUXADC_PDN_EN);
>  
>  	clk_disable_unprepare(adc_dev->adc_clk);
> +	mutex_destroy(&adc_dev->lock);
>  
>  	return 0;
>  }