GNU bug report logs - #29789
25.1; Emacs blocks user input when using visual-fill-column in wide terminals

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Luis Gerhorst <privat <at> luisgerhorst.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 25.1; Emacs blocks user input when using visual-fill-column in wide
 terminals
Date: Wed, 20 Dec 2017 20:28:27 +0100

1. Run Emacs in a wide terminal (about 150 characters, 100 isn't
enough): emacs -nw -Q

2. Load a arbitrary theme: M-x load-theme adwaita

3. Load visual-fill-column. E.g. by copying
https://raw.githubusercontent.com/joostkremers/visual-fill-column/c0e5ec8f88a7598f7afdee565978410bee0de2a0/visual-fill-column.el
into the scratch buffer and typing M-x eval-buffer.

There is nothing suspicious about the code, regular lisp code should not
be able to block Emacs (I believe). It does not seem to contain any loops that block the main thread. The maintainer knows about the issue but say's it may be an issue with low-level code. In GUI Emacs it works.

4. Open a buffer and enable visual-fill-column-mode: M-x
visual-fill-column-mode

5. Your Emacs is now blocked. In ZSH when I type C-g C-g I'm back in my
shell which displays the message "zsh: suspended emacs -nw -Q".

This bug has been encountered by multiple users on different operating
systems (Debian, Ubuntu and macOS) running different versions of Emacs
(24.5 to 26.0), some reported it here:
https://github.com/joostkremers/visual-fill-column/issues/1



In GNU Emacs 25.1.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2017-09-15, modified by Debian built on trouble
System Description:	Debian GNU/Linux 9.3 (stretch)

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/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --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/emacs25:/etc/emacs:/usr/local/share/emacs/25.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --with-x=yes --with-x-toolkit=gtk3
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 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
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NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11

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

Major mode: GFM

Minor modes in effect:
  luis-text-wrap-mode: t
  visual-fill-column-mode: t
  adaptive-wrap-prefix-mode: t
  diff-auto-refine-mode: t
  shell-dirtrack-mode: t
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  global-company-mode: t
  company-mode: t
  which-key-mode: t
  flx-ido-mode: t
  ido-vertical-mode: t
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  projectile-global-mode: t
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  override-global-mode: t
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  mouse-wheel-mode: t
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  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  visual-line-mode: t
  transient-mark-mode: t

Recent messages:
Source file ‘/home/cip/2016/un65esoq/.emacs.d/elpa/bind-key-2.3/bind-key.el’ newer than byte-compiled file
Loading /home/cip/2016/un65esoq/.emacs.d/recentf...done
Cleaning up the recentf list...done (0 removed)
Source file ‘/home/cip/2016/un65esoq/.emacs.d/elpa/s-1.12.0/s.el’ newer than byte-compiled file
Source file ‘/home/cip/2016/un65esoq/.emacs.d/elpa/company-0.9.4/company-dabbrev.el’ newer than byte-compiled file
Unable to load color "brightgreen" [12 times]
For information about GNU Emacs and the GNU system, type C-h C-a.
Mark saved where search started
Visual-Fill-Column mode enabled in current buffer
GNU Emacs 25.1.1 (x86_64-pc-linux-gnu, GTK+ Version 3.22.11) of 2017-09-15, modified by Debian

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Message #8 received at 29789 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Luis Gerhorst <privat <at> luisgerhorst.de>
Cc: 29789 <at> debbugs.gnu.org
Subject: Re: bug#29789: 25.1;
 Emacs blocks user input when using visual-fill-column in wide
 terminals
Date: Wed, 20 Dec 2017 22:29:27 +0200

> From: Luis Gerhorst <privat <at> luisgerhorst.de>
> Date: Wed, 20 Dec 2017 20:28:27 +0100
> 
> 
> 1. Run Emacs in a wide terminal (about 150 characters, 100 isn't
> enough): emacs -nw -Q
> 
> 2. Load a arbitrary theme: M-x load-theme adwaita
> 
> 3. Load visual-fill-column. E.g. by copying
> https://raw.githubusercontent.com/joostkremers/visual-fill-column/c0e5ec8f88a7598f7afdee565978410bee0de2a0/visual-fill-column.el
> into the scratch buffer and typing M-x eval-buffer.
> 
> There is nothing suspicious about the code, regular lisp code should not
> be able to block Emacs (I believe). It does not seem to contain any loops that block the main thread. The maintainer knows about the issue but say's it may be an issue with low-level code. In GUI Emacs it works.
> 
> 4. Open a buffer and enable visual-fill-column-mode: M-x
> visual-fill-column-mode
> 
> 5. Your Emacs is now blocked.

I tried to reproduce this on GNU/Linux and on MS-Windows, but failed
both times, both with Emacs 25.1 and the current emacs-26 release
branch.

What I see is that after enabling the mode, Emacs becomes somewhat
sluggish in cursor motion (hardly surprising, given what the mode
does), but it certainly doesn't hang.

I wonder what's different on your system, or on that of those who
confirmed the problem.

Message #11 received at 29789 <at> debbugs.gnu.org (full text, mbox):

From: Luis Gerhorst <privat <at> luisgerhorst.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: 29789 <at> debbugs.gnu.org
Subject: Re: bug#29789: 25.1;
 Emacs blocks user input when using visual-fill-column in wide
 terminals
Date: Wed, 20 Dec 2017 21:45:36 +0100

I'm usually using iTerm 3.1.5 and just tried again with the native
Terminal.app from macOS 10.13.2 (same issue). It also occured on a
Debian system I was running Emacs on over SSH.

I was not able to test with a non-macOS terminal emulator. I can do that
tomorrow however.

With 'hang' I meant that Emacs does not respond to user input at
all. The whole screen is frozen.

Eli Zaretskii writes:

>> From: Luis Gerhorst <privat <at> luisgerhorst.de>
>> Date: Wed, 20 Dec 2017 20:28:27 +0100
>>
>>
>> 1. Run Emacs in a wide terminal (about 150 characters, 100 isn't
>> enough): emacs -nw -Q
>>
>> 2. Load a arbitrary theme: M-x load-theme adwaita
>>
>> 3. Load visual-fill-column. E.g. by copying
>> https://raw.githubusercontent.com/joostkremers/visual-fill-column/c0e5ec8f88a7598f7afdee565978410bee0de2a0/visual-fill-column.el
>> into the scratch buffer and typing M-x eval-buffer.
>>
>> There is nothing suspicious about the code, regular lisp code should not
>> be able to block Emacs (I believe). It does not seem to contain any loops that block the main thread. The maintainer knows about the issue but say's it may be an issue with low-level code. In GUI Emacs it works.
>>
>> 4. Open a buffer and enable visual-fill-column-mode: M-x
>> visual-fill-column-mode
>>
>> 5. Your Emacs is now blocked.
>
> I tried to reproduce this on GNU/Linux and on MS-Windows, but failed
> both times, both with Emacs 25.1 and the current emacs-26 release
> branch.
>
> What I see is that after enabling the mode, Emacs becomes somewhat
> sluggish in cursor motion (hardly surprising, given what the mode
> does), but it certainly doesn't hang.
>
> I wonder what's different on your system, or on that of those who
> confirmed the problem.

Message #14 received at 29789 <at> debbugs.gnu.org (full text, mbox):

From: Vasilij Schneidermann <v.schneidermann <at> gmail.com>
To: 29789 <at> debbugs.gnu.org
Subject: Re: bug#29789: 25.1; Emacs blocks user input when using
 visual-fill-column in wide terminals
Date: Wed, 20 Dec 2017 22:35:30 +0100

[Message part 1 (text/plain, inline)]

I can reproduce this on Arch Linux, with Emacs master and Termite.  I've
tried making a full backtrace in gdb, let me know if there's anything
else I can do to help debugging this issue.

[gdb.txt (text/plain, attachment)]

Message #17 received at 29789 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Vasilij Schneidermann <v.schneidermann <at> gmail.com>
Cc: 29789 <at> debbugs.gnu.org
Subject: Re: bug#29789: 25.1;
 Emacs blocks user input when using visual-fill-column in wide
 terminals
Date: Thu, 21 Dec 2017 05:37:10 +0200

> Date: Wed, 20 Dec 2017 22:35:30 +0100
> From: Vasilij Schneidermann <v.schneidermann <at> gmail.com>
> 
> I can reproduce this on Arch Linux, with Emacs master and Termite.  I've
> tried making a full backtrace in gdb, let me know if there's anything
> else I can do to help debugging this issue.

Thanks.

> Thread 1 "emacs" received signal SIGTSTP, Stopped (user).
> 0x00007f5ccb9f9b47 in kill () from /usr/lib/libc.so.6
> Continuing.
> 
> Thread 1 "emacs" hit Breakpoint 1, terminate_due_to_signal (sig=6, 
>     backtrace_limit=40) at emacs.c:364
> 364	{
> #0  0x0000000000569e7a in terminate_due_to_signal (sig=6, backtrace_limit=40)
>     at emacs.c:364
> #1  0x00000000005919c8 in emacs_abort () at sysdep.c:2426
> #2  0x00000000005829d2 in handle_interrupt (in_signal_handler=true)
>     at keyboard.c:10501
> #3  0x0000000000582795 in handle_interrupt_signal (sig=2) at keyboard.c:10371
> #4  0x0000000000590f88 in deliver_process_signal (sig=2, handler=0x582743 <handle_interrupt_signal>) at sysdep.c:1709
> #5  0x00000000005827b4 in deliver_interrupt_signal (sig=2) at keyboard.c:10378
> #6  0x00007f5ccc8a9da0 in <signal handler called> () at /usr/lib/libpthread.so.0
> #7  0x00000000005083c0 in append_glyph (it=0x7ffcb39bc150) at term.c:1476
> #8  0x00000000005087d5 in produce_glyphs (it=0x7ffcb39bc150) at term.c:1584
> #9  0x00000000004722e7 in extend_face_to_end_of_line (it=0x7ffcb39bc150)
>     at xdisp.c:20318
> #10 0x00000000004773eb in display_line (it=0x7ffcb39bc150, cursor_vpos=3)
>     at xdisp.c:21740
> #11 0x0000000000469edf in try_window (window=XIL(0xd7f9a5), pos=..., flags=1)
>     at xdisp.c:17610
> #12 0x000000000046799c in redisplay_window (window=XIL(0xd7f9a5), just_this_one_p=false) at xdisp.c:17057
> #13 0x0000000000460734 in redisplay_window_0 (window=XIL(0xd7f9a5))
>     at xdisp.c:14814
> #14 0x000000000061975f in internal_condition_case_1 (bfun=0x4606f2 <redisplay_window_0>, arg=XIL(0xd7f9a5), handlers=XIL(0xd6bf13), hfun=0x4606ba <redisplay_window_error>) at eval.c:1356
> #15 0x000000000046068c in redisplay_windows (window=XIL(0xd7f9a5)) at xdisp.c:14794
> #16 0x000000000045f4b8 in redisplay_internal () at xdisp.c:14283
> #17 0x000000000045ff5e in redisplay_preserve_echo_area (from_where=2)
>     at xdisp.c:14613
> #18 0x0000000000426d03 in Fredisplay (force=XIL(0)) at dispnew.c:5828
> #19 0x000000000061d47a in funcall_subr (subr=0x951720 <Sredisplay>, numargs=0, args=Quit
> #0  0x0000000000569e7a in terminate_due_to_signal (sig=6, backtrace_limit=40)
>     at emacs.c:364
> #1  0x00000000005919c8 in emacs_abort () at sysdep.c:2426
> #2  0x00000000005829d2 in handle_interrupt (in_signal_handler=true)
>     at keyboard.c:10501
>         c = 121 'y'
> #3  0x0000000000582795 in handle_interrupt_signal (sig=2) at keyboard.c:10371
>         terminal = 0x12cfe40 <bss_sbrk_buffer+6086848>
> #4  0x0000000000590f88 in deliver_process_signal (sig=2, handler=0x582743 <handle_interrupt_signal>) at sysdep.c:1709
>         old_errno = 22
>         on_main_thread = true
> #5  0x00000000005827b4 in deliver_interrupt_signal (sig=2) at keyboard.c:10378
> #6  0x00007f5ccc8a9da0 in <signal handler called> () at /usr/lib/libpthread.so.0
> #7  0x00000000005083c0 in append_glyph (it=0x7ffcb39bc150) at term.c:1476
>         glyph = 0x7f5cd4622fd0
>         end = 0x7f5cd4622fd0
>         i = 0

This says Emacs got SIGINT and then aborted.  Did you type C-g more
then once and then answered YES to the question whether to abort and
dump core?

> #8  0x00000000005087d5 in produce_glyphs (it=0x7ffcb39bc150) at term.c:1584
> #9  0x00000000004722e7 in extend_face_to_end_of_line (it=0x7ffcb39bc150)
>     at xdisp.c:20318

The "hang" sounds like some infloop in redisplay.  It will be helpful
if instead of trying to interrupt Emacs with C-g, you could attach the
debugger, produce a backtrace from the place where Emacs was caught,
and then use the technique described in etc/DEBUG under "If the
symptom of the bug is that Emacs fails to respond", starting at "If
Emacs is in an infinite loop", to find out where it loops.

Also, I need to know what version of Emacs is that, to match line
numbers in the backtrace to the sources.

Message #20 received at 29789 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Vasilij Schneidermann <v.schneidermann <at> gmail.com>
Cc: 29789 <at> debbugs.gnu.org
Subject: Re: bug#29789: 25.1;
 Emacs blocks user input when using visual-fill-column in
 wide	terminals
Date: Thu, 21 Dec 2017 07:01:39 +0200

On December 21, 2017 5:37:10 AM GMT+02:00, Eli Zaretskii <eliz <at> gnu.org> wrote:
> > Date: Wed, 20 Dec 2017 22:35:30 +0100
> > From: Vasilij Schneidermann <v.schneidermann <at> gmail.com>
> > 
> > I can reproduce this on Arch Linux, with Emacs master and Termite. 
> I've
> > tried making a full backtrace in gdb, let me know if there's
> anything
> > else I can do to help debugging this issue.
> 
> Thanks.
> 
> > Thread 1 "emacs" received signal SIGTSTP, Stopped (user).
> > 0x00007f5ccb9f9b47 in kill () from /usr/lib/libc.so.6
> > Continuing.
> > 
> > Thread 1 "emacs" hit Breakpoint 1, terminate_due_to_signal (sig=6, 
> >     backtrace_limit=40) at emacs.c:364
> > 364	{
> > #0  0x0000000000569e7a in terminate_due_to_signal (sig=6,
> backtrace_limit=40)
> >     at emacs.c:364
> > #1  0x00000000005919c8 in emacs_abort () at sysdep.c:2426
> > #2  0x00000000005829d2 in handle_interrupt (in_signal_handler=true)
> >     at keyboard.c:10501
> > #3  0x0000000000582795 in handle_interrupt_signal (sig=2) at
> keyboard.c:10371
> > #4  0x0000000000590f88 in deliver_process_signal (sig=2,
> handler=0x582743 <handle_interrupt_signal>) at sysdep.c:1709
> > #5  0x00000000005827b4 in deliver_interrupt_signal (sig=2) at
> keyboard.c:10378
> > #6  0x00007f5ccc8a9da0 in <signal handler called> () at
> /usr/lib/libpthread.so.0
> > #7  0x00000000005083c0 in append_glyph (it=0x7ffcb39bc150) at
> term.c:1476
> > #8  0x00000000005087d5 in produce_glyphs (it=0x7ffcb39bc150) at
> term.c:1584
> > #9  0x00000000004722e7 in extend_face_to_end_of_line
> (it=0x7ffcb39bc150)
> >     at xdisp.c:20318
> > #10 0x00000000004773eb in display_line (it=0x7ffcb39bc150,
> cursor_vpos=3)
> >     at xdisp.c:21740
> > #11 0x0000000000469edf in try_window (window=XIL(0xd7f9a5), pos=...,
> flags=1)
> >     at xdisp.c:17610
> > #12 0x000000000046799c in redisplay_window (window=XIL(0xd7f9a5),
> just_this_one_p=false) at xdisp.c:17057
> > #13 0x0000000000460734 in redisplay_window_0 (window=XIL(0xd7f9a5))
> >     at xdisp.c:14814
> > #14 0x000000000061975f in internal_condition_case_1 (bfun=0x4606f2
> <redisplay_window_0>, arg=XIL(0xd7f9a5), handlers=XIL(0xd6bf13),
> hfun=0x4606ba <redisplay_window_error>) at eval.c:1356
> > #15 0x000000000046068c in redisplay_windows (window=XIL(0xd7f9a5))
> at xdisp.c:14794
> > #16 0x000000000045f4b8 in redisplay_internal () at xdisp.c:14283
> > #17 0x000000000045ff5e in redisplay_preserve_echo_area
> (from_where=2)
> >     at xdisp.c:14613
> > #18 0x0000000000426d03 in Fredisplay (force=XIL(0)) at
> dispnew.c:5828
> > #19 0x000000000061d47a in funcall_subr (subr=0x951720 <Sredisplay>,
> numargs=0, args=Quit
> > #0  0x0000000000569e7a in terminate_due_to_signal (sig=6,
> backtrace_limit=40)
> >     at emacs.c:364
> > #1  0x00000000005919c8 in emacs_abort () at sysdep.c:2426
> > #2  0x00000000005829d2 in handle_interrupt (in_signal_handler=true)
> >     at keyboard.c:10501
> >         c = 121 'y'
> > #3  0x0000000000582795 in handle_interrupt_signal (sig=2) at
> keyboard.c:10371
> >         terminal = 0x12cfe40 <bss_sbrk_buffer+6086848>
> > #4  0x0000000000590f88 in deliver_process_signal (sig=2,
> handler=0x582743 <handle_interrupt_signal>) at sysdep.c:1709
> >         old_errno = 22
> >         on_main_thread = true
> > #5  0x00000000005827b4 in deliver_interrupt_signal (sig=2) at
> keyboard.c:10378
> > #6  0x00007f5ccc8a9da0 in <signal handler called> () at
> /usr/lib/libpthread.so.0
> > #7  0x00000000005083c0 in append_glyph (it=0x7ffcb39bc150) at
> term.c:1476
> >         glyph = 0x7f5cd4622fd0
> >         end = 0x7f5cd4622fd0
> >         i = 0
> 
> This says Emacs got SIGINT and then aborted.  Did you type C-g more
> then once and then answered YES to the question whether to abort and
> dump core?
> 
> > #8  0x00000000005087d5 in produce_glyphs (it=0x7ffcb39bc150) at
> term.c:1584
> > #9  0x00000000004722e7 in extend_face_to_end_of_line
> (it=0x7ffcb39bc150)
> >     at xdisp.c:20318
> 
> The "hang" sounds like some infloop in redisplay.  It will be helpful
> if instead of trying to interrupt Emacs with C-g, you could attach the
> debugger, produce a backtrace from the place where Emacs was caught,
> and then use the technique described in etc/DEBUG under "If the
> symptom of the bug is that Emacs fails to respond", starting at "If
> Emacs is in an infinite loop", to find out where it loops.
> 
> Also, I need to know what version of Emacs is that, to match line
> numbers in the backtrace to the sources.

Forget it, I've succeeded in reproducing this.  The reason I couldn't before is because most themes do nothing if the terminal supports less than 89 colors (looks like their authors are just copying that condition from one another for no good reason), so I needed to find a theme which does work with fewer colors.

Message #23 received at 29789 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Luis Gerhorst <privat <at> luisgerhorst.de>
Cc: v.schneidermann <at> gmail.com, 29789 <at> debbugs.gnu.org
Subject: Re: bug#29789: 25.1;
 Emacs blocks user input when using visual-fill-column in
 wide	terminals
Date: Thu, 21 Dec 2017 19:49:13 +0200

> Date: Thu, 21 Dec 2017 07:01:39 +0200
> From: Eli Zaretskii <eliz <at> gnu.org>
> Cc: 29789 <at> debbugs.gnu.org
> 
> Forget it, I've succeeded in reproducing this.  The reason I
> couldn't before is because most themes do nothing if the terminal
> supports less than 89 colors (looks like their authors are just
> copying that condition from one another for no good reason), so I
> needed to find a theme which does work with fewer colors.

Ouch, what an embarrassingly stupid bug...

Should be fixed now on the emacs-26 branch.

Thanks.

Message #26 received at 29789 <at> debbugs.gnu.org (full text, mbox):

From: Luis Gerhorst <privat <at> luisgerhorst.de>
To: Eli Zaretskii <eliz <at> gnu.org>
Cc: v.schneidermann <at> gmail.com, 29789 <at> debbugs.gnu.org
Subject: Re: bug#29789: 25.1; Emacs blocks user input when using
 visual-fill-column in wide	terminals
Date: Thu, 21 Dec 2017 18:52:50 +0100

Great, big thanks to all of you!

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