bug#58956: mark_object, mark_objects(?) crash

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 3 Nov 2022 11:13:08 +0100
> From: Vincent Lefevre <vincent@vinc17.net>
> Cc: spwhitton@spwhitton.name, 58956@debbugs.gnu.org,
> 	1017711@bugs.debian.org
> 
> On 2022-11-03 08:47:06 +0200, Eli Zaretskii wrote:
> > > On 2022-11-02 14:24:51 +0200, Eli Zaretskii wrote:
> > > > Signal 1 is SIGHUP, AFAIU.  Why should Emacs receive SIGHUP in the
> > > > middle of GC, I have no idea.  Maybe ask the user what was he doing at
> > > > that time.  E.g., could that be a remote Emacs session?
> > > 
> > > No, it is on my local machine.
> > 
> > So how come Emacs gets a SIGHUP?  This is the crucial detail that is
> > missing here.  Basically, if SIGHUP is delivered to Emacs, Emacs is
> > supposed to die a violent death.
> 
> I suspect the SIGHUP comes from Emacs itself. According to strace
> output, the only processes started by Emacs are "/usr/bin/emacs"
> (there are many of them). I don't see what other process could be
> aware of the situation. Unfortunately, I couldn't reproduce the
> issue with strace (I suspect some race condition).
> 
> > > I run emacs, and quit it immediately. The generation of the core dump
> > > is almost 100% reproducible. Ditto with "emacs -nw".
> > 
> > Wait, you mean the crash is during exiting Emacs?
> 
> For this test, yes. In general, I don't know.
> 
> > That could mean Emacs receives some input event when it's half-way
> > through the shutdown process, and the input descriptor is already
> > closed.
> 
> Note that the process that crashes is not the Emacs I started,
> but a subprocess run by Emacs itself, since it has arguments like
> "-no-comp-spawn --batch -l /tmp/emacs-async-comp-url.el-FGov4z.el".

Andrea, could you please look into this?  The SIGHUP could be because
the parent process exits, but that shouldn't cause a crash in the
sub-process that performs native compilation?

Thanks.