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Bug#966692: stunnel4: FTBFS because of test hang

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On Thu, Aug 06, 2020 at 12:48:10AM +0200, Michał Mirosław wrote:
> On Thu, Aug 06, 2020 at 12:29:36AM +0300, Peter Pentchev wrote:
> > On Wed, Aug 05, 2020 at 10:52:31PM +0200, Michał Mirosław wrote:
> [...]
> > > Using print-debugging, I see that it stops at wait_for_child line just
> > > after printing the version. It seems that something is reaping the child
> > > before the main thread has a chance to wait for it.
> > 
> > OK, so the only thing that comes to my mind now is that you may be
> > hitting a crazy, crazy race between register_child() and child_reaper(),
> > and I say "a crazy, crazy race", because the test has to (apparently
> > reproducibly) receive the CHLD signal exactly between the check and
> > the creation in register_child()'s first "$children{...} //= ...cv"
> > statement.
> 
> Well, there is nothing that prevents SIGCHLD arriving between fork() and
> register_child(). You could test this with more confidence (though not
> 100%-reliably) by putting 'exit 1' just at the start of ($pid == 0) branch.

Nah, the problem is not just "between fork() and register_child()".
It really must arrive at a very specific moment in time, because
the //= operations for setting $children{$pid}{cv} try to make sure that
a new value is not set (that is, a new condition variable is not
created) if there already is such an element in the array. So the race
is indeed between the //= in register_child() and the //= in
child_reaper() - that is, child_reaper() must be invoked (SIGCHLD must
arrive) *during* the execution of the //= in register_child().

Unless I'm missing something, which is not at all out of the question :)

> > Can you apply the following patch and show me the output of running
> > the test?
> 
> Sure, but I got no patch. :-)

Oof. Not my day, is it... Here it is... I hope.

G'luck,
Peter

-- 
Peter Pentchev  roam@ringlet.net roam@debian.org pp@storpool.com
PGP key:        http://people.FreeBSD.org/~roam/roam.key.asc
Key fingerprint 2EE7 A7A5 17FC 124C F115  C354 651E EFB0 2527 DF13

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Bug#966692: stunnel4: FTBFS because of test hang Peter Pentchev <roam@ringlet.net> - 2020-08-02 16:50 +0200
  Bug#966692: stunnel4: FTBFS because of test hang Michał Mirosław <mirq-linux@rere.qmqm.pl> - 2020-08-05 20:10 +0200
    Bug#966692: stunnel4: FTBFS because of test hang Michał Mirosław <mirq-linux@rere.qmqm.pl> - 2020-08-06 01:00 +0200
      Bug#966692: stunnel4: FTBFS because of test hang Peter Pentchev <roam@ringlet.net> - 2020-08-06 02:30 +0200
        Bug#966692: stunnel4: FTBFS because of test hang Michał Mirosław <mirq-linux@rere.qmqm.pl> - 2020-08-06 02:50 +0200
          Bug#966692: stunnel4: FTBFS because of test hang Michał Mirosław <mirq-linux@rere.qmqm.pl> - 2020-08-06 03:30 +0200

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