bug#23842: 24.4; Runaway background process

[Ian Perryman <iperryman@xtreme-eda.com>]

In GNU Emacs 24.4.1 (x86_64-pc-linux-gnu, GTK+ Version 3.14.5)
 of 2015-03-07 on trouble, modified by Debian
Windowing system distributor `The XFree86 Project, Inc', version 11.0.40300000
System Description:	Debian GNU/Linux 8.2 (jessie)

Configured using:
 `configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.4/site-lisp:/usr/share/emacs/site-lisp
 --build x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes
 --enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.4/site-lisp:/usr/share/emacs/site-lisp
 --with-x=yes --with-x-toolkit=gtk3 --with-toolkit-scroll-bars
 'CFLAGS=-g -O2 -fstack-protector-strong -Wformat
 -Werror=format-security -Wall' CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-z,relro'

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

Major mode: Verilog

Minor modes in effect:
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<help-echo> C-x C-f <backspace> <backspace> <backspace> 
<backspace> <backspace> <backspace> v e r <tab> m o 
<tab> <return> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <menu-bar> <Verilog> 
<Version and FAQ> <help-echo> <help-echo> C-g C-g C-x 
1 C-n C-e M-? <help-echo> <down-mouse-1> <mouse-1> 
C-c C-c <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <help-echo> <help-echo> 
<help-echo> <help-echo> <help-echo> <menu-bar> <options> 
<debug-on-quit> M-? <down-mouse-1> <mouse-1> C-g C-g 
C-g C-a M-x r e p o r t - b u <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit [2 times]
Type SPC to continue editing.
command-execute: The mark is not set now, so there is no region
Debug on Quit enabled globally
Type SPC to continue editing.
Quit [3 times]

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
help-fns mail-prsvr mail-utils cus-start cus-load help-mode verilog-mode
easymenu compile comint ansi-color ring diff time-date tooltip electric
uniquify ediff-hook vc-hooks lisp-float-type mwheel x-win x-dnd tool-bar
dnd fontset image regexp-opt fringe tabulated-list newcomment lisp-mode
prog-mode register page menu-bar rfn-eshadow timer select scroll-bar
mouse jit-lock font-lock syntax facemenu font-core frame cham georgian
utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao korean
japanese hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese case-table epa-hook jka-cmpr-hook help simple abbrev
minibuffer nadvice loaddefs button faces cus-face macroexp files
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget hashtable-print-readable backquote make-network-process
dbusbind gfilenotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)

Memory information:
((conses 16 92747 8401)
 (symbols 48 20320 0)
 (miscs 40 51 199)
 (strings 32 16107 4632)
 (string-bytes 1 458706)
 (vectors 16 10684)
 (vector-slots 8 401945 6854)
 (floats 8 76 476)
 (intervals 56 254 0)
 (buffers 960 14)
 (heap 1024 46181 1524))



This version of Emacs came with

You are using verilog-mode 2013-11-05-78e66ba-vpo


The problem is reproducible as follows:

Open a new buffer called "moo.sv"

Paste this text into it without the tags:
<start of file>
module moo.sv;
   ini
<end of file>

Move point to the end of the second line.

Ensure that verilog-mode is enabled.  If it is not use "M-x
verilog-mode"

Press M-?

This will open a buffer with possible completions ... there will only be
one... "initial"

Use mouse-1 to select it.

This will cause the emacs session to start using 100% of the CPU (you
should have a top session running separately to notice.  However this
process is a background process and normal editing can continue until
the process uses up all available memory.  I kill it quickly using
"C-g".

The expected behavior is that the "ini" is expanded to "inital" and
editing continues with point after the word "initial".

What happens is that the emacs process starts consuming 100% CPU, and
eventually consume all the available memory in the background.  The
cursor is left at the end of line 2 after the word "ini".


Here is a dribble file including the C-g.  If you delete everything
after the C-g, you will see the bad behavior.


\x06moo.sv<return>module moo;ini<return><up> 0x800003f<help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><down-mouse-1><mouse-1>\a<help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo>\x13\x03


Another strange behavior is I tried to get a stack trace using C-g by
enabling "Enter Debugger on Quit/C-g".  When I press C-g, It does not
end up going into the debugger, but the background process what ever it
is, gets killed and CPU usage returns to normal, but no backtrace buffer
is opened.

Here is a trace of that (Again including the C-g):

<help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><menu-bar><options><debug-on-error><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><menu-bar><options><debug-on-quit>\x06moo.sv<return>module moo;ini<return><up> 0x800003f<help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><help-echo><down-mouse-1><mouse-1>\a\a\a\a\x13\x03


I have reported the issue to the folks who support the verilog-mode, and
they have requested I open the bug with you.

The bug is reported here
http://www.veripool.org/issues/1070-Verilog-mode-Auto-completion-results-in-runaway-emacs-process-in-emacs-24-4-on-Debian-using-2016-04-23-5f6855e-vpo

The emacs-mode I used in that report is newer than the one indicated
here, but they exhibit the same issue.  The version in this report is
what comes bundled with this version of emacs, so I assumed it would be
easier for you to reproduce.

Thanks for your help.

Ian Perryman