Re: [PATCH] [extcon]:remove freed groups caused the panic or warningin unregister flow

[Chanwoo Choi]

On 11/04/2013 11:07 AM, Wang, Xiaoming wrote:
> Dear Choi
> 
> -----Original Message-----
> From: Chanwoo Choi [mailto:cw00.choi@xxxxxxxxxxx] 
> Sent: Monday, November 04, 2013 9:43 AM
> To: Wang, Xiaoming
> Cc: myungjoo.ham@xxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Liu, Chuansheng; Zhang, Dongxing
> Subject: Re: [PATCH] [extcon]:remove freed groups caused the panic or warning in unregister flow
> 
> Hi Wang,
> 
>>  drivers/extcon/extcon-class.c |    3 ++-
>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/extcon/extcon-class.c 
>> b/drivers/extcon/extcon-class.c index 148382f..48f4669 100644
>> --- a/drivers/extcon/extcon-class.c
>> +++ b/drivers/extcon/extcon-class.c
>> @@ -794,6 +794,8 @@ void extcon_dev_unregister(struct extcon_dev *edev)
>>  		return;
>>  	}
>>  
>> +	device_unregister(edev->dev);
>> +
>>  	if (edev->mutually_exclusive && edev->max_supported) {
>>  		for (index = 0; edev->mutually_exclusive[index];
>>  				index++)
>> @@ -814,7 +816,6 @@ void extcon_dev_unregister(struct extcon_dev *edev)
>>  	if (switch_class)
>>  		class_compat_remove_link(switch_class, edev->dev, NULL);  #endif
>> -	device_unregister(edev->dev);
>>  	put_device(edev->dev);
>>  }
>>  EXPORT_SYMBOL_GPL(extcon_dev_unregister);
>>
> 
> I think we could only apply following patch instead of moving the position of device_unregister().
> 
> diff --git a/drivers/extcon/extcon-class.c b/drivers/extcon/extcon-class.c index 148382f..ff27b19 100644
> --- a/drivers/extcon/extcon-class.c
> +++ b/drivers/extcon/extcon-class.c
> @@ -805,10 +805,8 @@ void extcon_dev_unregister(struct extcon_dev *edev)
>         for (index = 0; index < edev->max_supported; index++)
>                 kfree(edev->cables[index].attr_g.name);
>  
> -       if (edev->max_supported) {
> -               kfree(edev->extcon_dev_type.groups);
> +       if (edev->max_supported)
>                 kfree(edev->cables);
> -       }
>  
>  #if defined(CONFIG_ANDROID)
>         if (switch_class)
> 
> Thanks,
> Chanwoo Choi
> 
> 	I don't agree with you.
> 	Why do not you want moving the position of device_unregister()?
> 	It will cause the memory leak if has not kfree edev->extcon_dev_type.groups as your patch do firstly. And if you think kfree edev->extcon_dev_type.groups is meaningless well then kfree edev->extcon_dev_type.groups in function exton_dev_register (line 756)also should be removed I think. What do you think?
> 

As you comment, my opinion has memory leak problem. My mistake.
But, I prefer to call 'device_unregister' at the end of extcon_dev_unregister().
To resolve kernel panic, I think we could use 'devm_kzalloc' instead of kzalloc/kfree.
What is your opinion about my approach?

Thanks,
Chanwoo Choi


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