Re: [PATCH net] eth: fbnic: fix race between concurrent hwmon sensor reads

[Andrew Lunn <andrew@lunn.ch>]

On Wed, Jun 24, 2026 at 11:51:29PM +0200, Andrew Lunn wrote:
> On Wed, Jun 24, 2026 at 01:05:14PM -0700, Zinc Lim wrote:
> > From: Zinc Lim <limzhineng2@gmail.com>
> > 
> > Reading an hwmon sensor
> 
> Since this is a hwmon related patch, it is a good idea to Cc: the
> hwmon Maintainer.
> 
> I don't know hwmon too well, i've never had to look at locking, but...
> 
> static int hwmon_thermal_get_temp(struct thermal_zone_device *tz, int *temp)
> {
> 	struct hwmon_thermal_data *tdata = thermal_zone_device_priv(tz);
> 	struct hwmon_device *hwdev = to_hwmon_device(tdata->dev);
> 	int ret;
> 	long t;
> 
> 	guard(mutex)(&hwdev->lock);
> 
> 	ret = hwdev->chip->ops->read(tdata->dev, hwmon_temp, hwmon_temp_input,
> 				     tdata->index, &t);
> 
> Could you explain why this lock in the hwmon core is not sufficient?
> It could be i'm reading it wrong, but it looks like the lock is shared
> by all hwmon instanced registered by a
> hwmon_device_register_with_info() call.

Documentation/hwmon/hwmon-kernel-api.rst 

When using ``[devm_]hwmon_device_register_with_info()`` to register the
hardware monitoring device, accesses using the associated access functions
are serialised by the hardware monitoring core. If a driver needs locking
for other functions such as interrupt handlers or for attributes which are
fully implemented in the driver, hwmon_lock() and hwmon_unlock() can be used
to ensure that calls to those functions are serialized.

	Andrew