linux-kernel - Re: [PATCH] hwmon: pmbus: protect read-modify-write with lock

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Message-ID: <5ecab585-7e74-ea9f-8d33-93ab024e1a14@nokia.com>
Date:   Mon, 3 Jun 2019 13:11:45 +0000
From:   "Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@...ia.com>
To:     "Adamski, Krzysztof (Nokia - PL/Wroclaw)" 
        <krzysztof.adamski@...ia.com>, Guenter Roeck <linux@...ck-us.net>,
        Jean Delvare <jdelvare@...e.com>
CC:     "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] hwmon: pmbus: protect read-modify-write with lock

Hi!

On 30/05/2019 08:45, Adamski, Krzysztof (Nokia - PL/Wroclaw) wrote:
> The operation done in the pmbus_update_fan() function is a
> read-modify-write operation but it lacks any kind of lock protection
> which may cause problems if run more than once simultaneously. This
> patch uses an existing update_lock mutex to fix this problem.
> 
> Signed-off-by: Krzysztof Adamski <krzysztof.adamski@...ia.com>
> ---
> 
> I'm resending this patch to proper recipients this time. Sorry if the
> previous submission confused anybody.
> 
>  drivers/hwmon/pmbus/pmbus_core.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index ef7ee90ee785..94adbede7912 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -268,6 +268,7 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
>  	int rv;
>  	u8 to;
>  
> +	mutex_lock(&data->update_lock);
>  	from = pmbus_read_byte_data(client, page,
>  				    pmbus_fan_config_registers[id]);
>  	if (from < 0)
> @@ -278,11 +279,15 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
>  		rv = pmbus_write_byte_data(client, page,
>  					   pmbus_fan_config_registers[id], to);
>  		if (rv < 0)
> -			return rv;
> +			goto out;
>  	}
>  
> -	return _pmbus_write_word_data(client, page,
> -				      pmbus_fan_command_registers[id], command);
> +	rv = _pmbus_write_word_data(client, page,
> +				    pmbus_fan_command_registers[id], command);
> +
> +out:
> +	mutex_lock(&data->update_lock);

This has to be mutex_unlock()...

> +	return rv;
>  }
>  EXPORT_SYMBOL_GPL(pmbus_update_fan);

-- 
Best regards,
Alexander Sverdlin.