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

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Message-ID: <20210717174432.7e69e4e9@jic23-huawei>
Date:   Sat, 17 Jul 2021 17:44:32 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Hui Liu <hui.liu@...iatek.com>
Cc:     <robh+dt@...nel.org>, <knaack.h@....de>, <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] iio: mtk-auxadc: add mutex_destroy

On Thu, 15 Jul 2021 17:35:23 +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,

We very very rarely bother to call mutex_destroy().  The reason is
that it is only a non noop in when mutex debugging is enabled and
that is only useful if there is a plausible route in which it could
be used after the mutex_destroy.   Given these are both at the ends
of removal paths, I don't think this is useful.  That's why you will
rarely find mutex_destroy() being called.

Thanks,

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;
>  }