linux-kernel - Re: [PATCH v3 2/5] iio: consumers: copy/release available info from producer to fix race

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Message-ID: <7qvxz3fuwcjeq2ewv3nterlf72wbymt7np5nnjitzkt6smzh7v@737455c4xapy>
Date: Wed, 16 Oct 2024 23:08:30 +0200
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Matteo Martelli <matteomartelli3@...il.com>
Cc: Jonathan Cameron <jic23@...nel.org>, 
	Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>, 
	Alisa-Dariana Roman <alisa.roman@...log.com>, Christian Eggers <ceggers@...i.de>, 
	Peter Rosin <peda@...ntia.se>, Paul Cercueil <paul@...pouillou.net>, linux-iio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-mips@...r.kernel.org, linux-pm@...r.kernel.org
Subject: Re: [PATCH v3 2/5] iio: consumers: copy/release available info from
 producer to fix race

Hi,

On Tue, Oct 15, 2024 at 01:06:35PM +0200, Matteo Martelli wrote:
> Consumers need to call the producer's read_avail_release_resource()
> callback after reading producer's available info. To avoid a race
> condition with the producer unregistration, change inkern
> iio_channel_read_avail() so that it copies the available info from the
> producer and immediately calls its release callback with info_exists
> locked.
> 
> Also, modify the users of iio_read_avail_channel_raw() and
> iio_read_avail_channel_attribute() to free the copied available buffers
> after calling these functions.
> 
> Signed-off-by: Matteo Martelli <matteomartelli3@...il.com>
> ---
> diff --git a/drivers/power/supply/ingenic-battery.c b/drivers/power/supply/ingenic-battery.c
> index 0a40f425c27723ccec49985b8b5e14a737b6a7eb..3db000d9fff9a7a6819631314547b3d16db7f967 100644
> --- a/drivers/power/supply/ingenic-battery.c
> +++ b/drivers/power/supply/ingenic-battery.c
> @@ -12,6 +12,7 @@
>  #include <linux/platform_device.h>
>  #include <linux/power_supply.h>
>  #include <linux/property.h>
> +#include <linux/slab.h>
>  
>  struct ingenic_battery {
>  	struct device *dev;
> @@ -79,8 +80,10 @@ static int ingenic_battery_set_scale(struct ingenic_battery *bat)
>  		dev_err(bat->dev, "Unable to read channel avail scale\n");
>  		return ret;
>  	}
> -	if (ret != IIO_AVAIL_LIST || scale_type != IIO_VAL_FRACTIONAL_LOG2)
> -		return -EINVAL;
> +	if (ret != IIO_AVAIL_LIST || scale_type != IIO_VAL_FRACTIONAL_LOG2) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
>  
>  	max_mV = bat->info->voltage_max_design_uv / 1000;
>  
> @@ -99,7 +102,8 @@ static int ingenic_battery_set_scale(struct ingenic_battery *bat)
>  
>  	if (best_idx < 0) {
>  		dev_err(bat->dev, "Unable to find matching voltage scale\n");
> -		return -EINVAL;
> +		ret = -EINVAL;
> +		goto out;
>  	}
>  
>  	/* Only set scale if there is more than one (fractional) entry */
> @@ -109,10 +113,13 @@ static int ingenic_battery_set_scale(struct ingenic_battery *bat)
>  						  scale_raw[best_idx + 1],
>  						  IIO_CHAN_INFO_SCALE);
>  		if (ret)
> -			return ret;
> +			goto out;
>  	}
>  
> -	return 0;
> +	ret = 0;
> +out:
> +	kfree(scale_raw);
> +	return ret;
>  }
>  
>  static enum power_supply_property ingenic_battery_properties[] = {

It should be enough to declare scale_raw like this at the beginning
of the function and otherwise keep it as is when you include
<linux/cleanup.h>:

const int *scale_raw __free(kfree) = NULL;

Greetings,

-- Sebastian

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