linux-kernel - Re: [PATCH] iio: gyro: ssp_gyro_sensor: Use devm_iio_device

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Date:	Mon, 21 Sep 2015 13:18:57 +0200
From:	Karol Wrona <k.wrona@...sung.com>
To:	Jonathan Cameron <jic23@...23.retrosnub.co.uk>,
	Jonathan Cameron <jic23@...nel.org>,
	Vaishali Thakkar <vthakkar1994@...il.com>
Cc:	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: gyro: ssp_gyro_sensor: Use devm_iio_device_register

On 09/21/2015 11:53 AM, Jonathan Cameron wrote:
> 
> 
> On 21 September 2015 09:18:39 BST, Karol Wrona <k.wrona@...sung.com> wrote:
>> On 09/20/2015 09:18 PM, Jonathan Cameron wrote:
>>> On 14/09/15 17:08, Vaishali Thakkar wrote:
>>>> Use resourced managed function devm_iio_device_register to
>>>> make error path simpler. To be compatible with the change,
>>>> the remove function is removed as it is now redundant.
>>>>
>>>> Signed-off-by: Vaishali Thakkar <vthakkar1994@...il.com>
>>> This patch is reasonable, but makes me wonder if there is an issue
>>> in the remove path for this driver.  It relies on the ssp_sensors
>> common
>>> module.  That in ssp_spi.c uses the fact ssp_register_consumer
>>> has saved the struct iio_dev into a local array in the core driver.
>>> I think this means that a remove of this function will leave a
>> possible
>>> null pointer de reference.
>> You are right. In this case we need something like
>> ssp_deregister_consumer(...) in ssp_dev.c. So I think that "remove
>> func"
>> should stay. Of course we can switch to devm iio register.
> Not if you want to remove the userspace interface before doing you new function call.  Doing so gives a nasty race.
So better leave it out:
iio_device_unregister(indio_dev) will disable the buffers and through
ops disables the sensor and than remove iio dev ptr from the internal table.


>>
>> Also the same can (rather should) be done for accelerometer sensor
>> (ssp_accel_sensor.c).
>>
>> Vaishali, if you want please feel free and send patch.
>>
>>>
>>> Now I suspect that case doesn't actually occur because the relevant
>>> device elements are disabled whenever this module is removed.  Having
>>> said that we might expect an ssp_unregister_consumer function that
>>> sets the relevant pointer back to null on removal so as to avoid
>>> any possible race conditions around driver removal / reprobing.
>>> A spot of defensive programming rather than necessarily a bug to be
>>> fixed!
>>>
>>> One little process thing. This driver was written by Karol so patches
>>> should probably always cc Karol as well as the more general
>>> maintainer / reviewers for IIO.  Added cc.
>>>
>>> Jonathan
>>>> ---
>>>>  drivers/iio/gyro/ssp_gyro_sensor.c | 12 +-----------
>>>>  1 file changed, 1 insertion(+), 11 deletions(-)
>>>>
>>>> diff --git a/drivers/iio/gyro/ssp_gyro_sensor.c
>> b/drivers/iio/gyro/ssp_gyro_sensor.c
>>>> index 0a8afdd..ac88de7 100644
>>>> --- a/drivers/iio/gyro/ssp_gyro_sensor.c
>>>> +++ b/drivers/iio/gyro/ssp_gyro_sensor.c
>>>> @@ -134,7 +134,7 @@ static int ssp_gyro_probe(struct platform_device
>> *pdev)
>>>>  
>>>>  	platform_set_drvdata(pdev, indio_dev);
>>>>  
>>>> -	ret = iio_device_register(indio_dev);
>>>> +	ret = devm_iio_device_register(&pdev->dev, indio_dev);
>>>>  	if (ret < 0)
>>>>  		return ret;
>>>>  
>>>> @@ -144,21 +144,11 @@ static int ssp_gyro_probe(struct
>> platform_device *pdev)
>>>>  	return 0;
>>>>  }
>>>>  
>>>> -static int ssp_gyro_remove(struct platform_device *pdev)
>>>> -{
>>>> -	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
>>>> -
>>>> -	iio_device_unregister(indio_dev);
>>>> -
>>>> -	return 0;
>>>> -}
>>>> -
>>>>  static struct platform_driver ssp_gyro_driver = {
>>>>  	.driver = {
>>>>  		.name = SSP_GYROSCOPE_NAME,
>>>>  	},
>>>>  	.probe = ssp_gyro_probe,
>>>> -	.remove = ssp_gyro_remove,
>>>>  };
>>>>  
>>>>  module_platform_driver(ssp_gyro_driver);
>>>>
>>>
>>> --
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> 

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