[LTP] [PATCH v3] fzsync: revoke thread_b if parent hits an accidental break

[Li Wang]

Hi Richard,

On Tue, Sep 24, 2019 at 8:42 PM Richard Palethorpe <rpalethorpe@suse.de>
wrote:

> ...
> It can just be
>
> if (!pair->exit) {
>    ...
> }
>
> We want to join the thread and set the func pointer to zero regardless
> of how we exit.
>

OK.


>
> > +                     SAFE_PTHREAD_JOIN(pair->thread_b, NULL);
> > +                     pair->thread_b = 0;
> > +             } else {
>
> I suggest still setting pair->exit here and maybe sleeping for
> 100ms. This gives thread B chance to exit gracefully. It is possible
> that if thread B is in a spin loop then the thread won't be cancelled as
> asynchronous cancellation is not guaranteed by POSIX.
>

Good suggestion. That'd be better to give one more time for thread B
exiting gracefully.


> > +                     pthread_cancel(pair->thread_b);
> > +                     pair->thread_b = 0;
> > +             }
> >       }
> >  }
> >
> > @@ -271,8 +276,11 @@ static void tst_fzsync_pair_reset(struct
> tst_fzsync_pair *pair,
> >       pair->a_cntr = 0;
> >       pair->b_cntr = 0;
> >       pair->exit = 0;
> > -     if (run_b)
> > +     if (run_b) {
> > +             pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
> > +             pthread_setcancelstate(PTHREAD_CANCEL_ENABLE, NULL);
>
> These need to go inside thread B unless I am mistaken. Which means you
>

Right.


> must wrap the user supplied function. You can create a function which
> accepts a pointer to some contiguous memory containing the user supplied
> function
> pointer and the user supplied arg pointer.
>

Since you have fixed the function format of thread B as void *(*run_b)(void
*) in tst_fzsync_pair_reset(), which means we have no need to take care of
the function arg pointer anymore.

So just like what I did in V2, the wrapper function could steal the real
run_b address from pthread_create(..., wrap_run_b, run_b) parameter.

-- 
Regards,
Li Wang
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