Re: [dpdk-stable] [PATCH] vdpa/mlx5: fix configuration mutex cleanup

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 1/21/21 9:13 PM, Matan Azrad wrote:
> 
> 
> From: Maxime Coquelin
>> On 1/14/21 4:23 PM, Matan Azrad wrote:
>>>
>>>
>>> From: Maxime Coquelin
>>>> On 1/14/21 2:09 PM, Matan Azrad wrote:
>>>>>
>>>>>
>>>>> From: Maxime Coquelin
>>>>>> Hi Matan,
>>>>>>
>>>>>> On 1/14/21 12:49 PM, Matan Azrad wrote:
>>>>>>> Hi Maxime and David
>>>>>>>
>>>>>>> Thank you for Review.
>>>>>>>
>>>>>>> From: David Marchand
>>>>>>>> On Fri, Jan 8, 2021 at 9:48 AM David Marchand
>>>>>>>> <david.marchand@redhat.com> wrote:
>>>>>>>>>> I wonder if it would be possible and cleaner to disable
>>>>>>>>>> cancellation on the thread while the mutex is held?
>>>>>>>
>>>>>>> Yes, we can cause thread to return by some global variable sync.
>>>>>>> It is the same logic.
>>>>>>
>>>>>> No, that was not my suggestion. My suggestion is to block the
>>>>>> thread cancellation while in the critical section, using
>> pthread_setcancelstate().
>>>>>
>>>>> Yes, Generally it is better to let the thread control his
>>>>> cancellation, either
>>>> cancel itself or enabling\disabling cancellations.
>>>>>
>>>>> I don't see a reason to wait for the thread in current logic - the
>>>>> critical section
>>>> is not important to be completed here.
>>>>
>>>> The reason I see is there are quite a few things done in this
>>>> critical section. And if tomorrow someone add new things in it, he
>>>> may not know the thread can be cancelled at any time, which could cause
>> hard to debug issues.
>>>
>>> As I said, here it is not needed, this thread designed just to cause guest
>> notifications.
>>>
>>> The optional future developer mistake can be done also outside the critical
>> section in in any other place - we cannot protect it.
>>>
>>> The design choice is to close the thread fast.
>>
>> But why is it so urgent that it cannot been stopped cleanly?
>> I don't think it would add seconds delay by doing it in a clean way.
> 
> We have system calls there per queue.
> No need this optional delay just because of mutex cleaning. 

OK, up to you...

And what about the timer lock?

> 
>  
>> Thanks,
>> Maxime
>>
>>>>> We just want to close the thread and to clean the mutex.
>>>>>
>>>>>>>>> +1
>>>>>>>>
>>>>>>>> IEEE Std 1003.1-2001/Cor 2-2004, item XBD/TC2/D6/26 is applied,
>>>>>>>> adding pthread_t to the list of types that are not required to be
>>>>>>>> arithmetic types, thus allowing pthread_t to be defined as a structure.
>>>>>>>>
>>>>>>>> It would be better to leave pthread_t alone and not interpret it:
>>>>>>>>
>>>>>>>> if (priv->timer_tid) {
>>>>>>>>     pthread_cancel(priv->timer_tid);
>>>>>>>>     pthread_join(priv->timer_tid, &status); }
>>>>>>>> priv->timer_tid = 0;
>>>>>>>
>>>>>>>
>>>>>>> I'm not sure why you think it is better in this specific case.
>>>>>>> The cancellation will close the thread in faster way, no need to
>>>>>>> wait for the
>>>>>> thread to close itself.
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> --
>>>>>>>> David Marchand
>>>>>>>
>>>>>
>>>
>