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

[Matan Azrad]

From: Maxime Coquelin
> > 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 at 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?

Existing code initiates it before reusing...

Thanks.

> 
> >
> >
> >> 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
> >>>>>>>
> >>>>>
> >>>
> >