From: Eli Zaretskii <eliz@gnu.org>
To: Stefan Monnier <monnier@IRO.UMontreal.CA>
Cc: fabrice.popineau@gmail.com, emacs-devel@gnu.org
Subject: Re: GC and stack marking
Date: Tue, 20 May 2014 19:57:01 +0300 [thread overview]
Message-ID: <8338g4bd7m.fsf@gnu.org> (raw)
In-Reply-To: <jwvbnusio3o.fsf-monnier+emacs@gnu.org>
> From: Stefan Monnier <monnier@IRO.UMontreal.CA>
> Cc: emacs-devel@gnu.org, Fabrice Popineau <fabrice.popineau@gmail.com>
> Date: Tue, 20 May 2014 09:44:05 -0400
>
> > The short version of the question is: is it possible that a Lisp
> > object which is no longer referenced by anything won't be GC'ed
> > because it is marked by mark_stack due to some kind of coincidence?
>
> Yes, of course, it's what makes a conservative marking conservative.
I have nothing against conservative, but this failure to GC is too
spectacular to ignore.
> > So the huge hash-table gets dumped into the emacs executable, and
>
> That's bad luck, indeed.
>
> > causes all kinds of trouble in the dumped Emacs.
>
> But it shouldn't cause any trouble (other than extra memory use).
It does, due to all kinds of subtleties. The result is that the
large_vectors linked list gets dumped with a pointer to a non-existent
memory, and the dumped Emacs then crashes on the first GC when it
tries to traverse that linked list.
> > If this can legitimately happen, then how can we make sure this
> > hash-table indeed gets GC'd before we dump Emacs?
>
> First we should make sure that even if this table is not GC'd, Emacs
> behaves correctly.
Fabrice might have found a work-around, so there is hope. I found a
way to kludge around it, but my solution is more fragile.
Otherwise, we probably have a bug that can appear in
> other situations.
>
> - find where the spurious "reference" is coming from and add code to set
> this reference to some other value
I think this is hopeless: I see this problem on a single system; two
others don't have it. It's just some semi-random garbage somehwre on
the stack.
next prev parent reply other threads:[~2014-05-20 16:57 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-19 16:31 GC and stack marking Eli Zaretskii
2014-05-19 18:47 ` Paul Eggert
2014-05-19 19:14 ` Eli Zaretskii
2014-05-19 19:58 ` Paul Eggert
2014-05-19 20:03 ` Eli Zaretskii
2014-05-19 20:17 ` Paul Eggert
2014-05-20 16:37 ` Eli Zaretskii
2014-05-20 13:44 ` Stefan Monnier
2014-05-20 16:57 ` Eli Zaretskii [this message]
2014-05-20 17:54 ` Stefan Monnier
2014-05-20 19:28 ` Eli Zaretskii
2014-05-20 22:01 ` Stefan Monnier
2014-05-21 2:48 ` Eli Zaretskii
2014-05-21 3:01 ` Stefan Monnier
2014-05-21 15:39 ` Eli Zaretskii
2014-05-21 15:57 ` Dmitry Antipov
2014-05-21 16:06 ` Dmitry Antipov
2014-05-21 16:55 ` Eli Zaretskii
2014-05-21 16:53 ` Eli Zaretskii
2014-05-21 17:40 ` Stefan Monnier
2014-05-21 17:58 ` Eli Zaretskii
2014-05-22 15:20 ` Eli Zaretskii
2014-05-22 16:14 ` Stefan Monnier
2014-05-24 12:03 ` Eli Zaretskii
2014-05-20 19:12 ` Daniel Colascione
2014-05-20 19:43 ` Eli Zaretskii
2014-05-20 22:03 ` Stefan Monnier
2014-05-21 2:51 ` Eli Zaretskii
2014-05-31 6:31 ` Florian Weimer
2014-05-31 14:24 ` Stefan Monnier
-- strict thread matches above, loose matches on Subject: below --
2014-05-21 19:31 Barry OReilly
2014-05-21 20:13 ` Eli Zaretskii
2014-05-21 20:49 ` Barry OReilly
2014-05-22 2:43 ` Eli Zaretskii
2014-05-22 3:12 ` Daniel Colascione
2014-05-22 5:37 ` David Kastrup
2014-05-22 13:57 ` Stefan Monnier
2014-05-22 15:49 ` Eli Zaretskii
2014-05-22 14:59 ` Barry OReilly
2014-05-22 17:03 ` Eli Zaretskii
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