linux-kernel - Re: [PATCH -next] i3c: master: svc: drop free_irq of devm_request

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Date:   Fri, 28 May 2021 09:43:58 +0800
From:   Yang Yingliang <yangyingliang@...wei.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-i3c@...ts.infradead.org>,
        <alexandre.belloni@...tlin.com>
Subject: Re: [PATCH -next] i3c: master: svc: drop free_irq of devm_request_irq
 allocated irq


On 2021/5/27 22:40, Miquel Raynal wrote:
> Hi Yang,
>
> Yang Yingliang <yangyingliang@...wei.com> wrote on Thu, 27 May 2021
> 21:49:53 +0800:
>
>> Hi,
>>
>> On 2021/5/27 18:01, Miquel Raynal wrote:
>>> Hi Yang,
>>>
>>> Yang Yingliang <yangyingliang@...wei.com> wrote on Tue, 18 May 2021
>>> 21:11:27 +0800:
>>>   
>>>> 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.
>>>>
>>>> Reported-by: Hulk Robot <hulkci@...wei.com>
>>>> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
>>>> ---
>>>>    drivers/i3c/master/svc-i3c-master.c | 2 +-
>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/i3c/master/svc-i3c-master.c b/drivers/i3c/master/svc-i3c-master.c
>>>> index 1f6ba4221817..761c9c468357 100644
>>>> --- a/drivers/i3c/master/svc-i3c-master.c
>>>> +++ b/drivers/i3c/master/svc-i3c-master.c
>>>> @@ -1448,7 +1448,7 @@ static int svc_i3c_master_remove(struct platform_device *pdev)
>>>>    	if (ret)
>>>>    		return ret;
>>>>    >> -	free_irq(master->irq, master);
>>>> +	devm_free_irq(&pdev->dev, master->irq, master);
>>> Wouldn't removing this call the right solution? If it's a device
>>> managed resource, it won't probably be needed to free it explicitly in
>>> the remove path.
>> Some drivers would expect to free irq itself,
> I don't get it. Drivers do not expect anything, they should just comply
> with the API. If robots complain because a device managed resource is
> being freed without the device managed helper, this does not mean that
> the resource should explicitly be freed, it just means that *if* it
> must be explicitly freed, the wrong helper is being used.
>
>> I am not sure if it's ok to remove the free_irq() in i3c,
> What is the link with I3C? Sorry I might be missing something but
> master->irq is a driver variable, I don't get the link with the I3C
> framework and why it would interfere.
>
>> I just keep the original logic here and avoid double free.
> I don't think it is sane. Calling devm_free_irq() maybe is the right
> solution - I don't feel like it is - but your certainly can't hide
> behind a 'I just want the robots to be happy' justification. Hiding
> bugs on purpose is not something that I personally appreciate much.
Freeing irq in ->remove() is earlier than in device manage framework, if
just remove the free_irq() in svc_i3c_master_remove() and free the irq by
device manage framework, I am not sure if it breaks the resource free
sequence in Silvaco I3C master driver. If it's OK, I can resend a patch with
removing the free_irq().

Thanks,
Yang
>
> Thanks,
> Miquèl
> .