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

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Date:	Thu, 26 Sep 2013 11:23:08 +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 10:36 AM, Jingoo Han wrote:
> On Thursday, September 26, 2013 11:13 AM, Wei Yongjun wrote:
>> 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.
> However, 'dev_id' is a pointer, not a value.
> It seems to make the problem that references the invalid pointer.

free_irq using dev_id as a raw data, so you mean the irq handle?

----
 free_irq(...)
 {
   ...
     if (action->dev_id == dev_id)
   ...
 }
---

Regards,
Yongjun Wei


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