Date:   Wed, 21 Jun 2017 22:32:26 +0800
From:   Jia-Ju Bai <baijiaju1990@....com>
To:     Kalle Valo <kvalo@...eaurora.org>
Cc:     David Miller <davem@...emloft.net>, manish.chopra@...ium.com,
        rahul.verma@...ium.com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>
Subject: Re: [PATCH] netxen: Fix a sleep-in-atomic bug in
 netxen_nic_pci_mem_access_direct

On 2017/6/21 21:40, Kalle Valo wrote:

> Jia-Ju Bai <baijiaju1990@....com> writes:
>
>> On 06/21/2017 02:11 PM, Kalle Valo wrote:
>>> David Miller<davem@...emloft.net>  writes:
>>>
>>>> From: Jia-Ju Bai<baijiaju1990@....com>
>>>> Date: Mon, 19 Jun 2017 10:48:53 +0800
>>>>
>>>>> The driver may sleep under a spin lock, and the function call path is:
>>>>> netxen_nic_pci_mem_access_direct (acquire the lock by spin_lock)
>>>>>     ioremap -->  may sleep
>>>>>
>>>>> To fix it, the lock is released before "ioremap", and the lock is
>>>>> acquired again after this function.
>>>>>
>>>>> Signed-off-by: Jia-Ju Bai<baijiaju1990@....com>
>>>> This style of change you are making is really starting to be a
>>>> problem.
>>>>
>>>> You can't just drop locks like this, especially without explaining
>>>> why it's ok, and why the mutual exclusion this code was trying to
>>>> achieve is still going to be OK afterwards.
>>>>
>>>> In fact, I see zero analysis of the locking situation here, why
>>>> it was needed in the first place, and why your change is OK in
>>>> that context.
>>>>
>>>> Any locking change is delicate, and you must put the greatest of
>>>> care and consideration into it.
>>>>
>>>> Just putting "unlock/lock" around the sleeping operation shows a
>>>> very low level of consideration for the implications of the change
>>>> you are making.
>>>>
>>>> This isn't like making whitespace fixes, sorry...
>>> We already tried to explain this to Jia-Ju during review of a wireless
>>> patch:
>>>
>>> https://patchwork.kernel.org/patch/9756585/
>>>
>>> Jia-Ju, you should listen to feedback. If you continue submitting random
>>> patches like this makes it hard for maintainers to trust your patches
>>> anymore.
>>>
>> Hi,
>>
>> I am quite sorry for my incorrect patches, and I will listen carefully
>> to your advice. In fact, for some bugs and patches which I have
>> reported before, I have not received the feedback of them, so I resent
>> them a few days ago, including this patch.
> Yeah, it is likely that some of your reports will not get any response.
> For that I only suggest being persistent and providing more information
> about the issue and suggestions how it might be possible to fix it. Also
> Dan Carpenter (Cced) might have some suggestions.
>
> But trying to "fix" it by just silencing the warning without proper
> analysis is totally the wrong approach, you do more harm than good.
>
> What tool do you use to find these issues? Is it publically available?
>

Hi,

Thanks a lot for your advice. And I am very glad to see that you may be 
interested in my work :)
This static tool is written by myself, instead of using or improving 
existing tools. A reason why I write it is that I have encountered some 
sleep-in-atomic bugs in my driver development :( .
However, due to preliminary implementation, this tool still has some 
limitations which can produce some false positives or negatives, and it 
may be not very easy to use. Thus, I am still improving this tool, 
checking more code and collecting results now. By the way, I apologize 
again for my incorrect patches of trying to "fix" the detected bugs.
In fact, I am very glad to make this tool available to effectively and 
conveniently check more system code. After I finish the improvements and 
perform more evaluation, I will make it publicly available.
If you have any suggestion or comment on my work, please feel free to 
contact me :)

Thanks,
Jia-Ju Bai

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