bug#28279: 25.2; repeatable crash when hitting C-g twice

bug#28279: 25.2; repeatable crash when hitting C-g twice

[Eric Hoffman]

I dont think its necessary, bu after 30 years I've developed the muscle
memory of hitting C-g twiceif I want to get back to a known state.
I've noticed this happening on OSX using a brew-installed 25.4, but
recently after noticing it on Freebsd, I compiled from source with
deubugging turned on. It doesn't happen every time, but usually about
once every 30 minutes with my particular usage

  OS: FreeBSD 11.0-RELEASE-p9
  Compiler: FreeBSD clang version 3.8.0 (tags/RELEASE_380/final 262564)
           (based on LLVM 3.8.0)
  Emacs: "25.2.1"
  Stacktrace:
  0x4af3e4 <emacs_backtrace+0x54> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x4938fc <terminate_due_to_signal+0x5c> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x4ad7a3 <emacs_abort+0x13> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x50c474 <Fsignal+0x4b4> at /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x512cf5 <Fassq+0x15> at /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x48cfbe <Fterminal_parameter+0x7e> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x48c1e7 <tty_send_additional_strings+0x17> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x48b7ef <tty_reset_terminal_modes+0x1f> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x4ae851 <reset_sys_modes+0x101> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x4ae738 <reset_all_sys_modes+0x18> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x49dce5 <handle_interrupt+0xb5> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x4aecd7 <deliver_process_signal+0x37> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
  0x80195378f <pthread_sigmask+0x4ff> at /lib/libthr.so.3
  0x801952d6f <pthread_getspecific+0xe9f> at /lib/libthr.so.3

If someone wants to track this down and wants more information, I can
try to run it in the debugger (i struggle some with lldb), or recompile
with instrumentation

as always, thanks for...emacs...I think the last time I filed a bug was
around 1990



In GNU Emacs 25.2.1 (x86_64-unknown-freebsd11.0)
 of 2017-08-23 built on zeitgeist.tenuki.org
Configured features:
SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Fundamental

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  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

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For information about GNU Emacs and the GNU system, type C-h C-a.
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Memory information:
((conses 16 87371 5095)
 (symbols 48 19375 0)
 (miscs 40 113 98)
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 (vector-slots 8 385356 12608)
 (floats 8 155 132)
 (intervals 56 127 3)
 (buffers 976 24))

bug#28279: 25.2; repeatable crash when hitting C-g twice

[Eli Zaretskii]

> From: Eric Hoffman <yuri@tenuki.org>
> Date: Tue, 29 Aug 2017 18:20:10 +0000
> 
> 
> I dont think its necessary, bu after 30 years I've developed the muscle
> memory of hitting C-g twiceif I want to get back to a known state.
> I've noticed this happening on OSX using a brew-installed 25.4, but
> recently after noticing it on Freebsd, I compiled from source with
> deubugging turned on. It doesn't happen every time, but usually about
> once every 30 minutes with my particular usage

Can you tell what do you do, before the double C-g, to trigger this?
Does this happen if you start "emacs -Q" and the type C-0g twice, for
example?

Thanks.

bug#28279: 25.2; repeatable crash when hitting C-g twice

[Glenn Morris]

Eric Hoffman wrote:

>   0x4ad7a3 <emacs_abort+0x13> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
>   0x50c474 <Fsignal+0x4b4> at /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
>   0x512cf5 <Fassq+0x15> at /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
>   0x48cfbe <Fterminal_parameter+0x7e> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
>   0x48c1e7 <tty_send_additional_strings+0x17> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1

This appears to be https://debbugs.gnu.org/17406

bug#28279: 25.2; repeatable crash when hitting C-g twice

[Eric Hoffman]

  rgm@gnu.org: This appears to be https://debbugs.gnu.org/17406

it may be related, the only minor difference is that dont get presented
with the normal abort query, it just stops.

   Can you tell what do you do, before the double C-g, to trigger this?
   Does this happen if you start "emacs -Q" and the type C-0g twice, for
   example?

sorry, I should have said 'quasi repeatable', I cant get it to happen
on a new emacs. I suspect I do this when there is a delay in response and
this is my way of trying to determine if its the network or emacs. which
means that correlation with gc activity as in 17406 is probably high.I will
I can probably try to verify that by making lots of trash

bug#28279: 25.2; repeatable crash when hitting C-g twice

[Eli Zaretskii]

> From: Glenn Morris <rgm@gnu.org>
> Date: Tue, 29 Aug 2017 15:38:44 -0400
> Cc: 28279@debbugs.gnu.org
> 
> Eric Hoffman wrote:
> 
> >   0x4ad7a3 <emacs_abort+0x13> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
> >   0x50c474 <Fsignal+0x4b4> at /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
> >   0x512cf5 <Fassq+0x15> at /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
> >   0x48cfbe <Fterminal_parameter+0x7e> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
> >   0x48c1e7 <tty_send_additional_strings+0x17> at  /usr/home/yuri/emacs-25.2/src/emacs-25.2.1
> 
> This appears to be https://debbugs.gnu.org/17406

Does the below look reasonable for a fix?

diff --git a/src/term.c b/src/term.c
index 87a4126..5042abf 100644
--- a/src/term.c
+++ b/src/term.c
@@ -156,13 +156,17 @@ static void
 tty_send_additional_strings (struct terminal *terminal, Lisp_Object sym)
 {
   Lisp_Object lisp_terminal;
-  Lisp_Object extra_codes;
   struct tty_display_info *tty = terminal->display_info.tty;
 
   XSETTERMINAL (lisp_terminal, terminal);
-  for (extra_codes = Fterminal_parameter (lisp_terminal, sym);
-       CONSP (extra_codes);
-       extra_codes = XCDR (extra_codes))
+  /* We use CDR_SAFE and assq_no_quit to avoid any form of quitting or
+     signaling an error, since this function can run as part of the
+     "emergency escape" procedure invoked in the middle of GC, where
+     quitting means we crash.  */
+  Lisp_Object extra_codes =
+    CDR_SAFE (assq_no_quit (sym,
+			    decode_live_terminal (lisp_terminal)->param_alist));
+  for ( ; CONSP (extra_codes); extra_codes = XCDR (extra_codes))
     {
       Lisp_Object string = XCAR (extra_codes);
       if (STRINGP (string))

bug#28279: 25.2; repeatable crash when hitting C-g twice

[Glenn Morris]

Eli Zaretskii wrote:

> Does the below look reasonable for a fix?

Sorry, I don't know. If you want a second opinion, ask Paul?

bug#28279: 25.2; repeatable crash when hitting C-g twice

[Eli Zaretskii]

> From: Glenn Morris <rgm@gnu.org>
> Cc: yuri@tenuki.org,  28279@debbugs.gnu.org
> Date: Thu, 31 Aug 2017 12:48:26 -0400
> 
> Eli Zaretskii wrote:
> 
> > Does the below look reasonable for a fix?
> 
> Sorry, I don't know. If you want a second opinion, ask Paul?

I just wrote code that does the same as the original one, but calls
assq_no_quit instead of Fassq and CDR_SAFE instead of Fcdr.  This
should not signal an error nor QUIT, which was the root cause for the
abort.