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

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

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.

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
>>>>>
>>>
>