linux-kernel - Re: [PATCH] iio/accel/bmc150: Improve unlocking of a mutex in two functions

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Date:   Wed, 25 Oct 2017 17:57:22 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     SF Markus Elfring <elfring@...rs.sourceforge.net>,
        linux-iio@...r.kernel.org, Hartmut Knaack <knaack.h@....de>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] iio/accel/bmc150: Improve unlocking of a mutex in two
 functions

Hi,

On 25-10-17 16:33, SF Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Wed, 25 Oct 2017 16:26:29 +0200
> 
> Add a jump target so that a call of the function "mutex_unlock" is mostly
> stored at the end of these function implementations.
> Replace five calls by goto statements.
> 
> This issue was detected by using the Coccinelle software.
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>   drivers/iio/accel/bmc150-accel-core.c | 32 ++++++++++++++------------------
>   1 file changed, 14 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/iio/accel/bmc150-accel-core.c b/drivers/iio/accel/bmc150-accel-core.c
> index 870f92ef61c2..f2a85a11a5e4 100644
> --- a/drivers/iio/accel/bmc150-accel-core.c
> +++ b/drivers/iio/accel/bmc150-accel-core.c
> @@ -554,18 +554,15 @@ static int bmc150_accel_get_axis(struct bmc150_accel_data *data,
>   
>   	mutex_lock(&data->mutex);
>   	ret = bmc150_accel_set_power_state(data, true);
> -	if (ret < 0) {
> -		mutex_unlock(&data->mutex);
> -		return ret;
> -	}
> +	if (ret < 0)
> +		goto unlock_after_failure;
>   
>   	ret = regmap_bulk_read(data->regmap, BMC150_ACCEL_AXIS_TO_REG(axis),
>   			       &raw_val, sizeof(raw_val));
>   	if (ret < 0) {
>   		dev_err(dev, "Error reading axis %d\n", axis);
>   		bmc150_accel_set_power_state(data, false);
> -		mutex_unlock(&data->mutex);
> -		return ret;
> +		goto unlock_after_failure;
>   	}
>   	*val = sign_extend32(le16_to_cpu(raw_val) >> chan->scan_type.shift,
>   			     chan->scan_type.realbits - 1);
> @@ -575,6 +572,10 @@ static int bmc150_accel_get_axis(struct bmc150_accel_data *data,
>   		return ret;
>   
>   	return IIO_VAL_INT;
> +
> +unlock_after_failure:
> +	mutex_unlock(&data->mutex);
> +	return ret;
>   }
>   
>   static int bmc150_accel_read_raw(struct iio_dev *indio_dev,

IMHO, if you do this, you should rework the function so that there is a single unlock call
at the end, not a separate one in in error label.

Could e.g. change this:

         ret = bmc150_accel_set_power_state(data, false);
         mutex_unlock(&data->mutex);
         if (ret < 0)
                 return ret;

         return IIO_VAL_INT;
}

To:

         ret = bmc150_accel_set_power_state(data, false);
         if (ret < 0)
                 goto unlock;

	ret = IIO_VAL_INT;
unlock:
         mutex_unlock(&data->mutex);

         return ret;
}

And also use the unlock label in the other cases, this is actually
quite a normal pattern. I see little use in a patch like this if there
are still 2 unlock paths after the patch.

Regards,

Hans





> @@ -1170,28 +1171,23 @@ static int bmc150_accel_trigger_set_state(struct iio_trigger *trig,
>   	mutex_lock(&data->mutex);
>   
>   	if (t->enabled == state) {
> -		mutex_unlock(&data->mutex);
> -		return 0;
> +		ret = 0;
> +		goto unlock;
>   	}
>   
>   	if (t->setup) {
>   		ret = t->setup(t, state);
> -		if (ret < 0) {
> -			mutex_unlock(&data->mutex);
> -			return ret;
> -		}
> +		if (ret < 0)
> +			goto unlock;
>   	}
>   
>   	ret = bmc150_accel_set_interrupt(data, t->intr, state);
> -	if (ret < 0) {
> -		mutex_unlock(&data->mutex);
> -		return ret;
> -	}
> +	if (ret < 0)
> +		goto unlock;
>   
>   	t->enabled = state;
> -
> +unlock:
>   	mutex_unlock(&data->mutex);
> -
>   	return ret;
>   }
>   
>