Re: [PATCH v3] iio: light: vcnl4000: Fix WARN_ON on uninitialized lock

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Tue, Jan 31, 2023 at 03:01:09PM +0100, Mårten Lindahl wrote:
> There are different init functions for the sensors in this driver in
> which only one initializes the generic vcnl4000_lock. With commit
> e21b5b1f2669 ("iio: light: vcnl4000: Preserve conf bits when toggle power")
> the vcnl4040 sensor started to depend on the lock, but it was missed to
> initialize it in vcnl4040's init function. This has not been visible
> until we run lockdep on it:
> 
>   DEBUG_LOCKS_WARN_ON(lock->magic != lock)
>   at kernel/locking/mutex.c:575 __mutex_lock+0x4f8/0x890
>   Call trace:
>   __mutex_lock
>   mutex_lock_nested
>   vcnl4200_set_power_state
>   vcnl4200_init
>   vcnl4000_probe
> 
> Fix this by initializing the lock in the probe function instead of doing
> it in the chip specific init functions.

Fine now, thanks!
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

> Fixes: e21b5b1f2669 ("iio: light: vcnl4000: Preserve conf bits when toggle power")
> Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
> ---
> 
> v3:
>  - Trimmed backtrace in commit message even more
>  - New line before mutex_init
> 
> v2:
>  - Trimmed backtrace in commit message
>  - Have 12 digit sha-1 id in Fixes tag
>  - Make the lock initialization in probe instead of in _init function
> 
>  drivers/iio/light/vcnl4000.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iio/light/vcnl4000.c b/drivers/iio/light/vcnl4000.c
> index cc1a2062e76d..69c5bc987e26 100644
> --- a/drivers/iio/light/vcnl4000.c
> +++ b/drivers/iio/light/vcnl4000.c
> @@ -199,7 +199,6 @@ static int vcnl4000_init(struct vcnl4000_data *data)
>  
>  	data->rev = ret & 0xf;
>  	data->al_scale = 250000;
> -	mutex_init(&data->vcnl4000_lock);
>  
>  	return data->chip_spec->set_power_state(data, true);
>  };
> @@ -1197,6 +1196,8 @@ static int vcnl4000_probe(struct i2c_client *client)
>  	data->id = id->driver_data;
>  	data->chip_spec = &vcnl4000_chip_spec_cfg[data->id];
>  
> +	mutex_init(&data->vcnl4000_lock);
> +
>  	ret = data->chip_spec->init(data);
>  	if (ret < 0)
>  		return ret;
> -- 
> 2.30.2
> 

-- 
With Best Regards,
Andy Shevchenko