From: Pip Cet <pipcet@protonmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: eller.helmut@gmail.com, gerd.moellmann@gmail.com,
yantar92@posteo.net, emacs-devel@gnu.org
Subject: Re: MPS: a random backtrace while toying with gdb
Date: Wed, 03 Jul 2024 14:35:16 +0000 [thread overview]
Message-ID: <mmX8KRhhXjl-FhfxTFnCPevO9u3drNXWTa8ropqiW5JwwqwsmuabgccUbgVSYH-PeTXrGXFblwTWqkF_Mc8C70GmIHHW8bPAbBCIcI9z0_k=@protonmail.com> (raw)
In-Reply-To: <868qyibsp4.fsf@gnu.org>
On Wednesday, July 3rd, 2024 at 11:50, Eli Zaretskii <eliz@gnu.org> wrote:
> > Date: Wed, 03 Jul 2024 11:31:48 +0000
>
> > From: Pip Cet pipcet@protonmail.com
> > Cc: Eli Zaretskii eliz@gnu.org, eller.helmut@gmail.com, gerd.moellmann@gmail.com, yantar92@posteo.net, emacs-devel@gnu.org
> >
> > So what are the proposed solutions that are still on the table? I can think of these:
> >
> > 1. block signals around MPS calls and block signals while the MPS SIGSEGV handler is running
> > 2. handle signals in a special thread
> > 3. switch Emacs to an event loop model and handle all signals asynchronously
>
>
> I'd start with the first half of (1). It is not clear to me that the
> other part is needed, and in any case we need a reproducer for it
> first.
Ihor's original SIGPROF-based reproducer works if you revert the (SIGPROF-specific) workaround by Helmut. What makes you think it can't happen with other signals (which, naturally, aren't as frequent or badly-timed as SIGPROF, which strikes precisely when the CPU is active)?
Obviously a reproducer is highly desirable in this case, but we shouldn't leave known and understood bugs in the code.
> Most of the crashes we've seen until now were not when the MPS
> handler was running. Also, didn't someone say that when the MPS
Ihor's first crash backlog (MPS: profiler) clearly shows that was the case: https://lists.gnu.org/archive/html/emacs-devel/2024-06/msg00568.html
> SIGSEGV handler is active, we could detect that from our code and
> return doing nothing?
Dropping the signal in the process.
> > (1) is hard to do because we'd need to hijack the SIGSEGV handler and/or modify MPS
> > (3) is a very major change which would mean permanently losing features we want
> > (2) is very easy to do, but gets complicated for SIGPROF (which needs to be on the thread it's profiling) and emergency breakout signals which need to modify the main thread's state.
> >
> > I've tried (2) and it fixes the specific reproducer I posted yesterday, as it should do in theory. I believe it's the most flexible approach which still gives us well-defined semantics for signal handlers. We'd need to add per-thread signals for the specific cases mentioned above. And, of course, its pthread-specific.
>
> Doing (2) adds a whole lot of complexity to Emacs.
You're right.
> Most importantly,
> we will be unable to access Lisp data safely, unwind-protect and the
> entire specpdl stuff generally cannot be used, and signaling an error
> would be fatal. So I'd rather avoid that.
Very good points, though I wonder to what extent our current code is safe...
Pip
next prev parent reply other threads:[~2024-07-03 14:35 UTC|newest]
Thread overview: 68+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-06-29 19:12 MPS: a random backtrace while toying with gdb Ihor Radchenko
2024-06-29 19:19 ` Pip Cet
2024-06-29 21:46 ` Gerd Möllmann
2024-06-30 4:55 ` Eli Zaretskii
2024-06-30 5:33 ` Gerd Möllmann
2024-06-30 6:16 ` Eli Zaretskii
2024-06-30 6:43 ` Gerd Möllmann
2024-06-30 8:52 ` Eli Zaretskii
2024-06-30 9:43 ` Gerd Möllmann
2024-06-30 10:05 ` Eli Zaretskii
2024-06-30 11:20 ` Gerd Möllmann
2024-06-30 12:16 ` Eli Zaretskii
2024-06-30 12:43 ` Gerd Möllmann
2024-06-30 9:36 ` Helmut Eller
2024-06-30 10:00 ` Eli Zaretskii
2024-06-30 10:24 ` Helmut Eller
2024-06-30 10:43 ` Eli Zaretskii
2024-06-30 18:42 ` Helmut Eller
2024-06-30 18:59 ` Gerd Möllmann
2024-06-30 19:25 ` Pip Cet
2024-06-30 19:49 ` Ihor Radchenko
2024-06-30 20:09 ` Eli Zaretskii
2024-06-30 20:32 ` Pip Cet
2024-07-01 11:07 ` Eli Zaretskii
2024-07-01 17:27 ` Pip Cet
2024-07-01 17:42 ` Ihor Radchenko
2024-07-01 18:08 ` Eli Zaretskii
2024-07-02 7:55 ` Pip Cet
2024-07-02 13:10 ` Eli Zaretskii
2024-07-02 14:24 ` Pip Cet
2024-07-02 14:57 ` Eli Zaretskii
2024-07-02 17:06 ` Pip Cet
2024-07-03 11:31 ` Pip Cet
2024-07-03 11:50 ` Eli Zaretskii
2024-07-03 14:35 ` Pip Cet [this message]
2024-07-03 15:41 ` Eli Zaretskii
2024-07-01 2:33 ` Eli Zaretskii
2024-07-01 6:05 ` Helmut Eller
2024-06-30 19:58 ` Eli Zaretskii
2024-06-30 21:08 ` Ihor Radchenko
2024-07-01 2:35 ` Eli Zaretskii
2024-07-01 11:13 ` Eli Zaretskii
2024-07-01 11:47 ` Ihor Radchenko
2024-07-01 12:33 ` Eli Zaretskii
2024-07-01 17:17 ` Ihor Radchenko
2024-07-01 17:44 ` Eli Zaretskii
2024-07-01 18:01 ` Ihor Radchenko
2024-07-01 18:16 ` Eli Zaretskii
2024-07-01 18:24 ` Ihor Radchenko
2024-07-01 18:31 ` Eli Zaretskii
2024-07-01 18:51 ` Ihor Radchenko
2024-07-01 19:05 ` Eli Zaretskii
2024-07-01 19:34 ` Gerd Möllmann
2024-07-01 20:00 ` Ihor Radchenko
2024-07-02 4:33 ` Gerd Möllmann
2024-07-02 7:05 ` Ihor Radchenko
2024-07-02 7:06 ` Gerd Möllmann
2024-07-01 18:19 ` Gerd Möllmann
2024-07-01 18:23 ` Eli Zaretskii
2024-06-30 11:07 ` Gerd Möllmann
2024-06-30 11:06 ` Gerd Möllmann
2024-06-30 11:05 ` Gerd Möllmann
2024-06-30 9:59 ` Pip Cet
2024-06-30 10:09 ` Eli Zaretskii
2024-06-30 10:16 ` Pip Cet
2024-06-30 10:34 ` Eli Zaretskii
2024-06-30 13:06 ` Pip Cet
2024-06-30 11:10 ` Gerd Möllmann
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