Re: [PATCH v3 0/3] kernel/notifier.c: avoid duplicate registration

From: Xiaoming Ni <nixiaoming@huawei.com>
To: Vasily Averin <vvs@virtuozzo.com>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>
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Subject: Re: [PATCH v3 0/3] kernel/notifier.c: avoid duplicate registration
Date: Tue, 10 Sep 2019 11:57:55 +0800	[thread overview]
Message-ID: <664674a5-5ed9-8f0a-27ae-b4b868e96bdb@huawei.com> (raw)
In-Reply-To: <0d245a97-1169-9ef2-e502-043ba80eaa8c@virtuozzo.com>

On 2019/7/17 19:15, Vasily Averin wrote:
> On 7/16/19 5:07 PM, Xiaoming Ni wrote:
>> On 2019/7/16 18:20, Vasily Averin wrote:
>>> On 7/16/19 5:00 AM, Xiaoming Ni wrote:
>>>> On 2019/7/15 13:38, Vasily Averin wrote:
>>>>> On 7/14/19 5:45 AM, Xiaoming Ni wrote:
>>>>>> On 2019/7/12 22:07, gregkh@linuxfoundation.org wrote:
>>>>>>> On Fri, Jul 12, 2019 at 09:11:57PM +0800, Xiaoming Ni wrote:
>>>>>>>> On 2019/7/11 21:57, Vasily Averin wrote:
>>>>>>>>> On 7/11/19 4:55 AM, Nixiaoming wrote:
>>>>>>>>>> On Wed, July 10, 2019 1:49 PM Vasily Averin wrote:
>>>>>>>>>>> On 7/10/19 6:09 AM, Xiaoming Ni wrote:
....
...
>>>>>>>> So in these two cases, is it more reasonable to trigger BUG() directly when checking for duplicate registration ?
>>>>>>>> But why does current notifier_chain_register() just trigger WARN() without exiting ?
>>>>>>>> notifier_chain_cond_register() direct exit without triggering WARN() ?
>>>>>>>
>>>>>>> It should recover from this, if it can be detected.  The main point is
>>>>>>> that not all apis have to be this "robust" when used within the kernel
>>>>>>> as we do allow for the callers to know what they are doing :)
>>>>>>>
>>>>>> In the notifier_chain_register(), the condition ( (*nl) == n) is the same registration of the same hook.
>>>>>>  We can intercept this situation and avoid forming a linked list ring to make the API more rob
...
...

> Yes, I'm agree, at present there are no difference between
> notifier_chain_cond_register() and notifier_chain_register()
> 
> Question is -- how to improve it.
> You propose to remove notifier_chain_cond_register() by some way.
> Another option is return an error, for some abstract callers who expect possible double registration.
> 
> Frankly speaking I prefer second one,
> however because of kernel do not have any such callers right now seems you are right, 
> and we can delete notifier_chain_cond_register().
> 
> So let me finally accept your patch-set.
> 
> Thank you,
> 	Vasily Averin
> 
> .
>

Dear Greg Kroah-Hartman
is there any other opinion on this patch set?
can you pick this series?

thanks
	Xiaoming Ni