From mboxrd@z Thu Jan  1 00:00:00 1970
From: Richard Palethorpe <rpalethorpe@suse.de>
Date: Wed, 25 Sep 2019 10:53:16 +0200
Subject: [LTP] [PATCH v3] fzsync: revoke thread_b if parent hits an
 accidental break
In-Reply-To: <CAEemH2f-5zcvrHep30tWubA7LTqOgKbeBbuN7PO+1h70e3B0hA@mail.gmail.com>
References: <20190924105801.7616-1-liwang@redhat.com>
 <87wodxkgr4.fsf@rpws.prws.suse.cz>
 <CAEemH2f-5zcvrHep30tWubA7LTqOgKbeBbuN7PO+1h70e3B0hA@mail.gmail.com>
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To: ltp@lists.linux.it

Hello,

Li Wang <liwang@redhat.com> writes:

> 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.

I think the function pointer signature would be 'void *(*run_b)(void)'
not 'void *(*run_b)(void *)'.

I doubt any test would need the arg though, because we only use one
thread and can store parameters in global variables. So you could remove
it and update the tests.

The user might need that arg if they are starting many threads, but for
now we don't have explicit support for that in the library.

>
> 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.


--
Thank you,
Richard.