linux-kernel - Re: [PATCH AUTOSEL 5.18 03/68] iio: st_sensors: Add a local lock for protecting odr

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Date:   Wed, 8 Jun 2022 10:26:51 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Sasha Levin <sashal@...nel.org>
CC:     <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Jonathan Cameron <jic23@...nel.org>,
        "Denis Ciocca" <denis.ciocca@...com>, <linus.walleij@...aro.org>,
        <lars@...afoo.de>, <andy.shevchenko@...il.com>,
        <aardelean@...iqon.com>, <cai.huoqing@...ux.dev>,
        <linux-iio@...r.kernel.org>
Subject: Re: [PATCH AUTOSEL 5.18 03/68] iio: st_sensors: Add a local lock
 for protecting odr

On Tue,  7 Jun 2022 13:47:29 -0400
Sasha Levin <sashal@...nel.org> wrote:

> From: Miquel Raynal <miquel.raynal@...tlin.com>
> 
> [ Upstream commit 474010127e2505fc463236470908e1ff5ddb3578 ]
> 
> Right now the (framework) mlock lock is (ab)used for multiple purposes:
> 1- protecting concurrent accesses over the odr local cache
> 2- avoid changing samplig frequency whilst buffer is running
> 
> Let's start by handling situation #1 with a local lock.
> 
> Suggested-by: Jonathan Cameron <jic23@...nel.org>
> Cc: Denis Ciocca <denis.ciocca@...com>
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> Link: https://lore.kernel.org/r/20220207143840.707510-7-miquel.raynal@bootlin.com
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

Hi Sasha,

This one is a cleanup rather than a fix. It's part of a long term move to stop
drivers using an internal lock (which works, but limits our ability to
change the core code).  No problem backporting it if it makes
taking some other fix easier, but I'm not immediately seeing such a patch.

Thanks,

Jonathan

> ---
>  .../iio/common/st_sensors/st_sensors_core.c   | 24 ++++++++++++++-----
>  include/linux/iio/common/st_sensors.h         |  3 +++
>  2 files changed, 21 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iio/common/st_sensors/st_sensors_core.c b/drivers/iio/common/st_sensors/st_sensors_core.c
> index fa9bcdf0d190..b92de90a125c 100644
> --- a/drivers/iio/common/st_sensors/st_sensors_core.c
> +++ b/drivers/iio/common/st_sensors/st_sensors_core.c
> @@ -71,16 +71,18 @@ static int st_sensors_match_odr(struct st_sensor_settings *sensor_settings,
>  
>  int st_sensors_set_odr(struct iio_dev *indio_dev, unsigned int odr)
>  {
> -	int err;
> +	int err = 0;
>  	struct st_sensor_odr_avl odr_out = {0, 0};
>  	struct st_sensor_data *sdata = iio_priv(indio_dev);
>  
> +	mutex_lock(&sdata->odr_lock);
> +
>  	if (!sdata->sensor_settings->odr.mask)
> -		return 0;
> +		goto unlock_mutex;
>  
>  	err = st_sensors_match_odr(sdata->sensor_settings, odr, &odr_out);
>  	if (err < 0)
> -		goto st_sensors_match_odr_error;
> +		goto unlock_mutex;
>  
>  	if ((sdata->sensor_settings->odr.addr ==
>  					sdata->sensor_settings->pw.addr) &&
> @@ -103,7 +105,9 @@ int st_sensors_set_odr(struct iio_dev *indio_dev, unsigned int odr)
>  	if (err >= 0)
>  		sdata->odr = odr_out.hz;
>  
> -st_sensors_match_odr_error:
> +unlock_mutex:
> +	mutex_unlock(&sdata->odr_lock);
> +
>  	return err;
>  }
>  EXPORT_SYMBOL_NS(st_sensors_set_odr, IIO_ST_SENSORS);
> @@ -361,6 +365,8 @@ int st_sensors_init_sensor(struct iio_dev *indio_dev,
>  	struct st_sensors_platform_data *of_pdata;
>  	int err = 0;
>  
> +	mutex_init(&sdata->odr_lock);
> +
>  	/* If OF/DT pdata exists, it will take precedence of anything else */
>  	of_pdata = st_sensors_dev_probe(indio_dev->dev.parent, pdata);
>  	if (IS_ERR(of_pdata))
> @@ -554,18 +560,24 @@ int st_sensors_read_info_raw(struct iio_dev *indio_dev,
>  		err = -EBUSY;
>  		goto out;
>  	} else {
> +		mutex_lock(&sdata->odr_lock);
>  		err = st_sensors_set_enable(indio_dev, true);
> -		if (err < 0)
> +		if (err < 0) {
> +			mutex_unlock(&sdata->odr_lock);
>  			goto out;
> +		}
>  
>  		msleep((sdata->sensor_settings->bootime * 1000) / sdata->odr);
>  		err = st_sensors_read_axis_data(indio_dev, ch, val);
> -		if (err < 0)
> +		if (err < 0) {
> +			mutex_unlock(&sdata->odr_lock);
>  			goto out;
> +		}
>  
>  		*val = *val >> ch->scan_type.shift;
>  
>  		err = st_sensors_set_enable(indio_dev, false);
> +		mutex_unlock(&sdata->odr_lock);
>  	}
>  out:
>  	mutex_unlock(&indio_dev->mlock);
> diff --git a/include/linux/iio/common/st_sensors.h b/include/linux/iio/common/st_sensors.h
> index 22f67845cdd3..db4a1b260348 100644
> --- a/include/linux/iio/common/st_sensors.h
> +++ b/include/linux/iio/common/st_sensors.h
> @@ -237,6 +237,7 @@ struct st_sensor_settings {
>   * @hw_irq_trigger: if we're using the hardware interrupt on the sensor.
>   * @hw_timestamp: Latest timestamp from the interrupt handler, when in use.
>   * @buffer_data: Data used by buffer part.
> + * @odr_lock: Local lock for preventing concurrent ODR accesses/changes
>   */
>  struct st_sensor_data {
>  	struct iio_trigger *trig;
> @@ -261,6 +262,8 @@ struct st_sensor_data {
>  	s64 hw_timestamp;
>  
>  	char buffer_data[ST_SENSORS_MAX_BUFFER_SIZE] ____cacheline_aligned;
> +
> +	struct mutex odr_lock;
>  };
>  
>  #ifdef CONFIG_IIO_BUFFER