linux-kernel - Re: [PATCH v5 1/2] iio: adc: ti-ads7950: Fix improper use of mlock

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Date:   Sat, 9 Mar 2019 17:29:36 +0100
From:   Tomasz Duszynski <tduszyns@...il.com>
To:     justinpopo6@...il.com
Cc:     linux-iio@...r.kernel.org, linux-gpio@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com, f.fainelli@...il.com,
        bgolaszewski@...libre.com, linus.walleij@...aro.org,
        jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
        pmeerw@...erw.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/2] iio: adc: ti-ads7950: Fix improper use of mlock

On Fri, Mar 08, 2019 at 02:03:27PM -0800, justinpopo6@...il.com wrote:
> From: Justin Chen <justinpopo6@...il.com>
>
> Indio->mlock is used for protecting the different iio device modes.
> It is currently not being used in this way. Replace the lock with
> an internal lock specifically used for protecting the SPI transfer
> buffer.
>
> Signed-off-by: Justin Chen <justinpopo6@...il.com>
> ---
>  drivers/iio/adc/ti-ads7950.c | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/iio/adc/ti-ads7950.c b/drivers/iio/adc/ti-ads7950.c
> index 0ad6359..1e47bef 100644
> --- a/drivers/iio/adc/ti-ads7950.c
> +++ b/drivers/iio/adc/ti-ads7950.c
> @@ -56,6 +56,9 @@ struct ti_ads7950_state {
>  	struct spi_message	ring_msg;
>  	struct spi_message	scan_single_msg;
>
> +	/* Lock to protect the spi xfer buffers */
> +	struct mutex		slock;
> +
>  	struct regulator	*reg;
>  	unsigned int		vref_mv;
>
> @@ -268,6 +271,7 @@ static irqreturn_t ti_ads7950_trigger_handler(int irq, void *p)
>  	struct ti_ads7950_state *st = iio_priv(indio_dev);
>  	int ret;
>
> +	mutex_lock(&st->slock);
>  	ret = spi_sync(st->spi, &st->ring_msg);
>  	if (ret < 0)
>  		goto out;
> @@ -276,6 +280,7 @@ static irqreturn_t ti_ads7950_trigger_handler(int irq, void *p)
>  					   iio_get_time_ns(indio_dev));
>
>  out:
> +	mutex_unlock(&st->slock);
>  	iio_trigger_notify_done(indio_dev->trig);
>
>  	return IRQ_HANDLED;
> @@ -286,7 +291,7 @@ static int ti_ads7950_scan_direct(struct iio_dev *indio_dev, unsigned int ch)
>  	struct ti_ads7950_state *st = iio_priv(indio_dev);
>  	int ret, cmd;
>
> -	mutex_lock(&indio_dev->mlock);
> +	mutex_lock(&st->slock);
>
>  	cmd = TI_ADS7950_CR_WRITE | TI_ADS7950_CR_CHAN(ch) | st->settings;
>  	st->single_tx = cmd;
> @@ -298,7 +303,7 @@ static int ti_ads7950_scan_direct(struct iio_dev *indio_dev, unsigned int ch)
>  	ret = st->single_rx;
>
>  out:
> -	mutex_unlock(&indio_dev->mlock);
> +	mutex_unlock(&st->slock);
>
>  	return ret;
>  }
> @@ -432,16 +437,19 @@ static int ti_ads7950_probe(struct spi_device *spi)
>  	if (ACPI_COMPANION(&spi->dev))
>  		st->vref_mv = TI_ADS7950_VA_MV_ACPI_DEFAULT;
>
> +	mutex_init(&st->slock);
> +
>  	st->reg = devm_regulator_get(&spi->dev, "vref");
>  	if (IS_ERR(st->reg)) {
>  		dev_err(&spi->dev, "Failed get get regulator \"vref\"\n");
> -		return PTR_ERR(st->reg);
> +		ret = PTR_ERR(st->reg);
> +		goto error_destroy_mutex;
>  	}
>
>  	ret = regulator_enable(st->reg);
>  	if (ret) {
>  		dev_err(&spi->dev, "Failed to enable regulator \"vref\"\n");
> -		return ret;
> +		goto error_destroy_mutex;
>  	}
>
>  	ret = iio_triggered_buffer_setup(indio_dev, NULL,
> @@ -463,6 +471,8 @@ static int ti_ads7950_probe(struct spi_device *spi)
>  	iio_triggered_buffer_cleanup(indio_dev);
>  error_disable_reg:
>  	regulator_disable(st->reg);
> +error_destroy_mutex:
> +	mutex_destroy(&st->slock);

If your intention was to do resources cleanup then this is not
what this api was designed for. This is actually for debugging unwanted
subsequent mutex usage.

>
>  	return ret;
>  }
> @@ -475,6 +485,7 @@ static int ti_ads7950_remove(struct spi_device *spi)
>  	iio_device_unregister(indio_dev);
>  	iio_triggered_buffer_cleanup(indio_dev);
>  	regulator_disable(st->reg);
> +	mutex_destroy(&st->slock);
>
>  	return 0;
>  }
> --
> 2.7.4
>