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

From: Guenter Roeck
Date: Thu May 30 2019 - 13:25:02 EST


Hi,

On Thu, May 30, 2019 at 06:45:48AM +0000, 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@xxxxxxxxx>
> ---
>
> 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);

Should be mutex_unlock(), meaning you have not tested this ;-).

Either case, I think this is unnecessary. The function is (or should be)
always called with the lock already taken (ie with pmbus_set_sensor()
in the call path). If not, we would need a locked and an unlocked version
of this function to avoid lock recursion.

Thanks,
Guenter

> + return rv;
> }
> EXPORT_SYMBOL_GPL(pmbus_update_fan);
>
> --
> 2.20.1
>