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

["Mårten Lindahl" <martenli@axis.com>]

On 1/30/23 18:30, Jonathan Cameron wrote:
> On Mon, 30 Jan 2023 15:10:40 +0100
> Mårten Lindahl <martenli@axis.com> wrote:
>
>> On 1/30/23 14:04, Jonathan Cameron wrote:
>>> On Mon, 30 Jan 2023 10:37:42 +0100
>>> Mårten Lindahl <marten.lindahl@axis.com> wrote:
>>>   
>>>> There are different init functions for the sensors in this driver in
>>>> which only one initialize the generic vcnl4000_lock. With commit
>>>> e21b5b1f2 ("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)
>>>>     WARNING: CPU: 1 PID: 8800 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
>>>>      i2c_device_probe
>>>>      really_probe
>>>>      __driver_probe_device
>>>>      driver_probe_device
>>>>      __driver_attach
>>>>      bus_for_each_dev
>>>>      driver_attach
>>>>      bus_add_driver
>>>>      driver_register
>>>>      i2c_register_driver
>>>>      vcnl4000_driver_init
>>>>      do_one_initcall
>>>>      do_init_module
>>>>      load_module
>>>>      __do_sys_finit_module
>>>>      ...
>>>>
>>>> Fix this by adding mutex_init on the lock in the init function used for
>>>> vcnl4040.
>>>>
>>>> Fixes: e21b5b1f2 ("iio: light: vcnl4000: Preserve conf bits when toggle power")
>>>> Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>
>>> Perhaps better to pull the lock out of the device specific setup?
>> Hi Jonathan!
>>
>> Ok, having a
>>
>> static DEFINE_MUTEX(vcnl4000_lock);
>>
> No. Definitely don't do that.  We need one per device instance.
>
> I just meant move the mutex_init() into the main probe function rather
> than the chip specific init that is called from there.

Ok, sorry for the missunderstanding. I''ll fix it.

Kind regards

Mårten

>
>> will make sure initializing it wont be forgotten for specific setups.
>>
>> I'll test it.
>>
>> Kind regards
>>
>> Mårten
>>
>>>   
>>>> ---
>>>>    drivers/iio/light/vcnl4000.c | 1 +
>>>>    1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/iio/light/vcnl4000.c b/drivers/iio/light/vcnl4000.c
>>>> index cc1a2062e76d..a8a9fc3b1a02 100644
>>>> --- a/drivers/iio/light/vcnl4000.c
>>>> +++ b/drivers/iio/light/vcnl4000.c
>>>> @@ -316,6 +316,7 @@ static int vcnl4200_init(struct vcnl4000_data *data)
>>>>    	}
>>>>    	mutex_init(&data->vcnl4200_al.lock);
>>>>    	mutex_init(&data->vcnl4200_ps.lock);
>>>> +	mutex_init(&data->vcnl4000_lock);
>>>>    
>>>>    	ret = data->chip_spec->set_power_state(data, true);
>>>>    	if (ret < 0)