linux-kernel - Re: [PATCH v2 09/16] iio: adc: ad7768-1: remove unnecessary locking

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <b8c68fef-3427-4617-989d-20529d9293dc@baylibre.com>
Date: Mon, 27 Jan 2025 16:46:17 -0600
From: David Lechner <dlechner@...libre.com>
To: Jonathan Santos <Jonathan.Santos@...log.com>, linux-iio@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: lars@...afoo.de, Michael.Hennerich@...log.com,
 marcelo.schmitt@...log.com, jic23@...nel.org, robh@...nel.org,
 krzk+dt@...nel.org, conor+dt@...nel.org, jonath4nns@...il.com,
 marcelo.schmitt1@...il.com
Subject: Re: [PATCH v2 09/16] iio: adc: ad7768-1: remove unnecessary locking

On 1/27/25 9:13 AM, Jonathan Santos wrote:
> The current locking is only preventing a triggered buffer Transfer and a
> debugfs register access from happening at the same time. If a register
> access happens during a buffered read, the action is doomed to fail anyway,
> since we need to write a magic value to exit continuous read mode.
> 
> Remove locking from the trigger handler and use
> iio_device_claim_direct_mode() instead in the register access function.
> 
> Signed-off-by: Jonathan Santos <Jonathan.Santos@...log.com>
> ---
> v2 Changes:
> * New patch in v2. It replaces the guard(mutex) patch. 
> ---
>  drivers/iio/adc/ad7768-1.c | 23 ++++++++++-------------
>  1 file changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/iio/adc/ad7768-1.c b/drivers/iio/adc/ad7768-1.c
> index 17a49bf74637..5e2093be9b92 100644
> --- a/drivers/iio/adc/ad7768-1.c
> +++ b/drivers/iio/adc/ad7768-1.c
> @@ -271,16 +271,16 @@ static int ad7768_reg_access(struct iio_dev *indio_dev,
>  	struct ad7768_state *st = iio_priv(indio_dev);
>  	int ret;
>  
> -	mutex_lock(&st->lock);
> -	if (readval) {
> +	ret = iio_device_claim_direct_mode(indio_dev);
> +	if (ret)
> +		return ret;
> +
> +	if (readval)
>  		ret = regmap_read(st->regmap, reg, readval);
> -		if (ret)
> -			goto err_unlock;
> -	} else {
> +	else
>  		ret = regmap_write(st->regmap, reg, writeval);
> -	}
> -err_unlock:
> -	mutex_unlock(&st->lock);
> +
> +	iio_device_release_direct_mode(indio_dev);
>  
>  	return ret;
>  }
> @@ -495,18 +495,15 @@ static irqreturn_t ad7768_trigger_handler(int irq, void *p)
>  	struct ad7768_state *st = iio_priv(indio_dev);
>  	int ret;
>  
> -	mutex_lock(&st->lock);
> -
>  	ret = spi_read(st->spi, &st->data.scan.chan, 3);
>  	if (ret < 0)
> -		goto err_unlock;
> +		goto out;
>  
>  	iio_push_to_buffers_with_timestamp(indio_dev, &st->data.scan,
>  					   iio_get_time_ns(indio_dev));
>  
> -err_unlock:
> +out:
>  	iio_trigger_notify_done(indio_dev->trig);
> -	mutex_unlock(&st->lock);
>  
>  	return IRQ_HANDLED;
>  }

I think the lock can be fully removed from struct ad7768_state  if it isn't
being used anymore (and remove mutex_init() in probe()).