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

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Date:	Mon, 21 Sep 2015 10:53:29 +0100
From:	Jonathan Cameron <jic23@...23.retrosnub.co.uk>
To:	Karol Wrona <k.wrona@...sung.com>,
	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 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.
>
>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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