linux-kernel - Re: [PATCH] netxen: Fix a sleep-in-atomic bug in netxen_nic_pci_mem_access

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Message-ID: <8737atv4pm.fsf@kamboji.qca.qualcomm.com>
Date:   Wed, 21 Jun 2017 16:40:53 +0300
From:   Kalle Valo <kvalo@...eaurora.org>
To:     Jia-Ju Bai <baijiaju1990@....com>
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

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?

-- 
Kalle Valo