netdev - Re: [PATCH] moxa: drop free_irq of devm_request

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Message-ID: <CAPgLHd9VXaPx18ujDKbUik6XjOsnARcK-C-orCOynyJaWFREjw@mail.gmail.com>
Date:	Thu, 26 Sep 2013 10:12:53 +0800
From:	Wei Yongjun <weiyj.lk@...il.com>
To:	jg1.han@...sung.com
Cc:	jonas.jensen@...il.com, davem@...emloft.net,
	grant.likely@...aro.org, rob.herring@...xeda.com,
	yongjun_wei@...ndmicro.com.cn, netdev@...r.kernel.org,
	sachin.kamat@...aro.org
Subject: Re: [PATCH] moxa: drop free_irq of devm_request_irq allocated irq

On 09/26/2013 08:47 AM, Jingoo Han wrote:
> On Wednesday, September 25, 2013 4:33 PM, Wei Yongjun wrote:
>> From: Wei Yongjun <yongjun_wei@...ndmicro.com.cn>
>>
>> irq allocated with devm_request_irq should not be freed using
>> free_irq, because doing so causes a dangling pointer, and a
>> subsequent double free.
>>
>> Signed-off-by: Wei Yongjun <yongjun_wei@...ndmicro.com.cn>
>> ---
>>  drivers/net/ethernet/moxa/moxart_ether.c | 1 -
>>  1 file changed, 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/moxa/moxart_ether.c b/drivers/net/ethernet/moxa/moxart_ether.c
>> index 83c2091..9a7fcb5 100644
>> --- a/drivers/net/ethernet/moxa/moxart_ether.c
>> +++ b/drivers/net/ethernet/moxa/moxart_ether.c
>> @@ -531,7 +531,6 @@ static int moxart_remove(struct platform_device *pdev)
>>  	struct net_device *ndev = platform_get_drvdata(pdev);
>>
>>  	unregister_netdev(ndev);
>> -	free_irq(ndev->irq, ndev);
>>  	moxart_mac_free_memory(ndev);
>>  	free_netdev(ndev);
> CC'ed Sachin Kamat,
>
> In this case, the free_irq() will be called, after calling
> free_netdev(). 'ndev' is freed by free_netdev(). Then, 'ndev->irq'
> is used by free_irq(). Is it right?
>
> In my humble opinion, it seems to make the problem.
>

devm_request_irq() has recorded the irq and dev_id, so free_irq() by devm_*
will not touch 'ndev' which has been freed by free_netdev().
So, if we not need to call free_irq() before free_netdev(), there will be
no problem.


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