bug#61940: 29.0.60; Occasional crash when moving point continously with visual line numbers

[Simon Pugnet]

Eli Zaretskii <eliz@gnu.org> writes:

> > From: Simon Pugnet <simon@polaris64.net>
> > Cc: 61940@debbugs.gnu.org
> > Date: Fri, 03 Mar 2023 16:38:00 +0000
> >
> > > I'm not sure I understand what you mean by "attaching to a 
> > > running
> > > instance of Emacs which crashed".  If Emacs crashed, then it no 
> > > longer
> > > is running, so what exactly happens when Emacs "crashes", and how 
> > > do
> > > you attach GDB to such a "crashed" session?
> >
> > I used `gdb --pid=PID' to attach to the process which had crashed 
> > (or 
> > was at least not redrawing or accepting any user input).
>
> This seems to indicate that Emacs didn't crash, but stop responding
> for some reason.  In which case the backtrace you show doesn't tell
> anything interesting, it just tells us that Emacs is waiting for
> input.

Sorry, yes I realise now that I said "crash" in the subject but I 
meant that it hung or stopped responding to input. What I see when 
this happens is a plain white frame (background colour of the theme) 
and no keyboard or mouse input seems to be accepted.


> > From there I obtained the backtrace and was able to step, which is
> > how I noticed that it seemed to be in a loop. I might have 
> > diagnosed
> > this incorrectly however.
>
> The file etc/DEBUG in the Emacs repository has instructions for how 
> to
> identify the code in which Emacs is looping, if it's looping.  Look
> for "If the symptom of the bug is that Emacs fails to respond".

I managed to trigger this situation again this morning while working. 
Unfortunately I was unable to trigger it while it was being debugged 
in gdb; the problem occurs rarely so it's not easy to reproduce on 
demand.

I tried sending a SIGUSR2 signal to the running process multiple times 
but this did not appear to have any effect.

I again attached to the running process with gdb and ran "thread apply 
all bt" as instructed, here's the output: -

Thread 5 (Thread 0x7f11d37fe6c0 (LWP 35081) "threaded-ml"):
#0  0x00007f11e8d139df in poll () at /usr/lib/libc.so.6
#1  0x00007f11e051f8c7 in  () at /usr/lib/libpulse.so.0
#2  0x00007f11e050946c in pa_mainloop_poll () at 
/usr/lib/libpulse.so.0
#3  0x00007f11e051342c in pa_mainloop_iterate () at 
/usr/lib/libpulse.so.0
#4  0x00007f11e05134e1 in pa_mainloop_run () at /usr/lib/libpulse.so.0
#5  0x00007f11e0523c02 in  () at /usr/lib/libpulse.so.0
#6  0x00007f11e04c0c57 in  () at 
/usr/lib/pulseaudio/libpulsecommon-16.1.so
#7  0x00007f11e8c9ebb5 in  () at /usr/lib/libc.so.6
#8  0x00007f11e8d20d90 in  () at /usr/lib/libc.so.6

Thread 4 (Thread 0x7f11e23756c0 (LWP 35076) "dconf worker"):
#0  0x00007f11e8d139df in poll () at /usr/lib/libc.so.6
#1  0x00007f11ec662c2f in  () at /usr/lib/libglib-2.0.so.0
#2  0x00007f11ec60a0e2 in g_main_context_iteration () at 
/usr/lib/libglib-2.0.so.0
#3  0x00007f11e23cefde in  () at 
/usr/lib/gio/modules/libdconfsettings.so
#4  0x00007f11ec638db5 in  () at /usr/lib/libglib-2.0.so.0
#5  0x00007f11e8c9ebb5 in  () at /usr/lib/libc.so.6
#6  0x00007f11e8d20d90 in  () at /usr/lib/libc.so.6

Thread 3 (Thread 0x7f11e2bf96c0 (LWP 35075) "gdbus"):
#0  0x00007f11e8d139df in poll () at /usr/lib/libc.so.6
#1  0x00007f11ec662c2f in  () at /usr/lib/libglib-2.0.so.0
#2  0x00007f11ec60ad8f in g_main_loop_run () at 
/usr/lib/libglib-2.0.so.0
#3  0x00007f11ec860aec in  () at /usr/lib/libgio-2.0.so.0
#4  0x00007f11ec638db5 in  () at /usr/lib/libglib-2.0.so.0
#5  0x00007f11e8c9ebb5 in  () at /usr/lib/libc.so.6
#6  0x00007f11e8d20d90 in  () at /usr/lib/libc.so.6

Thread 2 (Thread 0x7f11e33fa6c0 (LWP 35074) "gmain"):
#0  0x00007f11e8d139df in poll () at /usr/lib/libc.so.6
#1  0x00007f11ec662c2f in  () at /usr/lib/libglib-2.0.so.0
#2  0x00007f11ec60a0e2 in g_main_context_iteration () at 
/usr/lib/libglib-2.0.so.0
#3  0x00007f11ec60a132 in  () at /usr/lib/libglib-2.0.so.0
#4  0x00007f11ec638db5 in  () at /usr/lib/libglib-2.0.so.0
#5  0x00007f11e8c9ebb5 in  () at /usr/lib/libc.so.6
#6  0x00007f11e8d20d90 in  () at /usr/lib/libc.so.6

Thread 1 (Thread 0x7f11e55fa2c0 (LWP 35073) "emacs"):
#0  0x00007f11e8d139df in poll () at /usr/lib/libc.so.6
#1  0x00007f11ec43726b in  () at /usr/lib/libxcb.so.1
#2  0x00007f11ec438d1d in xcb_wait_for_event () at 
/usr/lib/libxcb.so.1
#3  0x00007f11ec49ab09 in _XReadEvents () at /usr/lib/libX11.so.6
#4  0x00007f11ec48143a in XIfEvent () at /usr/lib/libX11.so.6
#5  0x00007f11ec4c7f10 in  () at /usr/lib/libX11.so.6
#6  0x00007f11ec4bf523 in  () at /usr/lib/libX11.so.6
#7  0x00007f11ec4c847c in _XimRead () at /usr/lib/libX11.so.6
#8  0x00007f11ec4b8d6c in  () at /usr/lib/libX11.so.6
#9  0x00007f11ec4a3c5f in XSetICValues () at /usr/lib/libX11.so.6
#10 0x0000563eb62f9d0b in xic_set_preeditarea (w=0x563ec43bdc60, 
x=287, y=493) at xfns.c:3176
#11 0x0000563eb62e5194 in handle_one_xevent 
(dpyinfo=dpyinfo@entry=0x563eb8c67800, 
event=event@entry=0x7ffce40dc7e0, finish=finish@entry=0x563eb6994270 
<current_finish>, hold_quit=0x7ffce40dcac0) at xterm.c:20116
#12 0x0000563eb62ecec1 in event_handler_gdk (gxev=0x7ffce40dc7e0, 
ev=<optimized out>, data=<optimized out>) at xterm.c:17447
#13 0x00007f11ed4d1b0f in  () at /usr/lib/libgdk-3.so.0
#14 0x00007f11ed4d96d5 in  () at /usr/lib/libgdk-3.so.0
#15 0x00007f11ed47f029 in gdk_display_get_event () at 
/usr/lib/libgdk-3.so.0
#16 0x00007f11ed4d9a68 in  () at /usr/lib/libgdk-3.so.0
#17 0x00007f11ec60b82b in g_main_context_dispatch () at 
/usr/lib/libglib-2.0.so.0
#18 0x00007f11ec662cc9 in  () at /usr/lib/libglib-2.0.so.0
#19 0x00007f11ec60a0e2 in g_main_context_iteration () at 
/usr/lib/libglib-2.0.so.0
#20 0x00007f11ecdd8eeb in gtk_main_iteration () at 
/usr/lib/libgtk-3.so.0
#21 0x0000563eb62d783a in XTread_socket (terminal=<optimized out>, 
hold_quit=0x7ffce40dcac0) at xterm.c:24819
#22 0x0000563eb6322f61 in gobble_input () at keyboard.c:7417
#23 0x0000563eb6323335 in handle_async_input () at keyboard.c:7648
#24 process_pending_signals () at keyboard.c:7662
#25 0x0000563eb63ac12d in probably_quit () at eval.c:1661
#26 0x0000563eb63c0a50 in maybe_quit () at 
/storage/Work/personal/emacs/src/lisp.h:3689
#27 Fassoc (key=0x7f11e4b9eb0c, alist=0x7f11e501828b, testfn=0x0) at 
fns.c:1969
#28 0x0000563eb6338ab4 in silly_event_symbol_error (c=0xb6d0) at 
keymap.c:1476
#29 Fdefine_key (keymap=0x563ebcc2ab53, key=0x563eb91ea1f5, 
def=0x563ebc515d0d, remove=0x0) at keymap.c:1165
#30 0x00007f11d11835c8 in 
F666c796d616b652d2d6d6f64652d6c696e652d636f756e746572_flymake__mode_line_counter_0 
() at 
/home/simon/.emacs.d/eln-cache/29.0.60-eff26154/flymake-a41dd277-ddccfc08.eln
#31 0x0000563eb63b0247 in eval_sub (form=form@entry=0x563ebb1208c3) at 
eval.c:2501
#32 0x0000563eb63b2876 in Feval (form=0x563ebb1208c3, 
lexical=<optimized out>) at eval.c:2361
#33 0x0000563eb63ac3b6 in Ffuncall (nargs=nargs@entry=2, 
args=args@entry=0x7ffce40dcfc0) at eval.c:2995
#34 0x0000563eb63aace1 in internal_condition_case_n 
(bfun=0x563eb63ac2c0 <Ffuncall>, nargs=nargs@entry=2, 
args=args@entry=0x7ffce40dcfc0, handlers=handlers@entry=0x30, 
hfun=hfun@entry=0x563eb621cb60 <safe_eval_handler>) at eval.c:1558
#35 0x0000563eb6207ecb in safe__call 
(inhibit_quit=inhibit_quit@entry=true, nargs=nargs@entry=2, 
func=func@entry=0x6930, ap=ap@entry=0x7ffce40dd040) at xdisp.c:3024
#36 0x0000563eb6207ff0 in safe__call1 
(inhibit_quit=inhibit_quit@entry=true, fn=fn@entry=0x6930) at 
xdisp.c:3060
#37 0x0000563eb62389a5 in safe__eval (sexpr=<optimized out>, 
inhibit_quit=true) at xdisp.c:3074
#38 display_mode_element (it=it@entry=0x7ffce40ddb50, depth=15, 
depth@entry=13, field_width=0, precision=precision@entry=-101, 
elt=0x563ebb1208b3, props=props@entry=0x7f11e4a9ac13, risky=false) at 
xdisp.c:27205
#39 0x0000563eb6238b21 in display_mode_element 
(it=it@entry=0x7ffce40ddb50, depth=13, depth@entry=12, 
field_width=field_width@entry=-8, precision=precision@entry=-100, 
elt=0x563ebb120ed3, props=0x7f11e4a9ac13, risky=<optimized out>) at 
/storage/Work/personal/emacs/src/lisp.h:754
#40 0x0000563eb62371ff in display_mode_element 
(it=it@entry=0x7ffce40ddb50, depth=12, depth@entry=10, 
field_width=-8, precision=precision@entry=-100, elt=0x563ebb120813, 
props=props@entry=0x7f11e4a9ac13, risky=false) at xdisp.c:27228
#41 0x0000563eb6238b21 in display_mode_element 
(it=it@entry=0x7ffce40ddb50, depth=10, depth@entry=7, field_width=0, 
precision=precision@entry=-92, elt=0x563ebb120e13, 
props=props@entry=0x7f11e4a9ac13, risky=<optimized out>) at 
/storage/Work/personal/emacs/src/lisp.h:754
#42 0x0000563eb6238b21 in display_mode_element 
(it=it@entry=0x7ffce40ddb50, depth=7, depth@entry=5, field_width=0, 
precision=precision@entry=-80, elt=0x563ebb405ed3, 
props=props@entry=0x7f11e4a9ac13, risky=<optimized out>) at 
/storage/Work/personal/emacs/src/lisp.h:754
#43 0x0000563eb6238b21 in display_mode_element 
(it=it@entry=0x7ffce40ddb50, depth=5, depth@entry=4, 
field_width=field_width@entry=0, precision=precision@entry=-80, 
elt=0x7f11e4a9aca3, props=0x7f11e4a9ac13, risky=<optimized out>) at 
/storage/Work/personal/emacs/src/lisp.h:754
#44 0x0000563eb62371ff in display_mode_element 
(it=it@entry=0x7ffce40ddb50, depth=4, depth@entry=3, field_width=0, 
precision=precision@entry=-80, elt=0x7f11e4a9abf3, 
props=props@entry=0x0, risky=false) at xdisp.c:27228
#45 0x0000563eb6238b21 in display_mode_element 
(it=it@entry=0x7ffce40ddb50, depth=3, depth@entry=1, field_width=0, 
precision=precision@entry=-76, elt=0x7f11e4a9a8ab, 
props=props@entry=0x0, risky=<optimized out>) at 
/storage/Work/personal/emacs/src/lisp.h:754
#46 0x0000563eb6238b21 in display_mode_element 
(it=it@entry=0x7ffce40ddb50, depth=1, depth@entry=0, 
field_width=field_width@entry=0, precision=precision@entry=0, 
elt=0x7f11e470fadb, elt@entry=0x7f11e470fa4b, props=props@entry=0x0, 
risky=<optimized out>) at /storage/Work/personal/emacs/src/lisp.h:754
#47 0x0000563eb623a620 in display_mode_line (w=w@entry=0x563ec43bdc60, 
face_id=MODE_LINE_ACTIVE_FACE_ID, format=0x7f11e470fa4b) at 
xdisp.c:26717
#48 0x0000563eb623c8ad in display_mode_lines 
(w=w@entry=0x563ec43bdc60) at xdisp.c:26630
#49 0x0000563eb6251d39 in redisplay_window (window=0x563ec43bdc65, 
just_this_one_p=just_this_one_p@entry=false) at xdisp.c:20364
#50 0x0000563eb6255a1b in redisplay_window_0 
(window=window@entry=0x563ec43bdc65) at xdisp.c:17446
#51 0x0000563eb63aaad4 in internal_condition_case_1 
(bfun=bfun@entry=0x563eb62559f0 <redisplay_window_0>, 
arg=arg@entry=0x563ec43bdc65, handlers=<optimized out>, 
hfun=hfun@entry=0x563eb620b960 <redisplay_window_error>) at 
eval.c:1498
#52 0x0000563eb62090a8 in redisplay_windows (window=0x563ec43bdc65) at 
xdisp.c:17416
#53 0x0000563eb623dce2 in redisplay_internal () at xdisp.c:16866
#54 0x0000563eb623f095 in redisplay () at xdisp.c:16049
#55 0x0000563eb632a483 in read_char (commandflag=1, 
map=map@entry=0x563ec421b423, prev_event=0x0, 
used_mouse_menu=used_mouse_menu@entry=0x7ffce40e30db, 
end_time=end_time@entry=0x0) at keyboard.c:2627
#56 0x0000563eb632cdb3 in read_key_sequence 
(keybuf=keybuf@entry=0x7ffce40e3210, prompt=prompt@entry=0x0, 
dont_downcase_last=dont_downcase_last@entry=false, 
can_return_switch_frame=can_return_switch_frame@entry=true, 
fix_current_buffer=fix_current_buffer@entry=true, 
prevent_redisplay=prevent_redisplay@entry=false) at keyboard.c:10074
#57 0x0000563eb632ec75 in command_loop_1 () at keyboard.c:1375
#58 0x0000563eb63aaa47 in internal_condition_case 
(bfun=bfun@entry=0x563eb632eab0 <command_loop_1>, 
handlers=handlers@entry=0x90, hfun=hfun@entry=0x563eb6321ac0 
<cmd_error>) at eval.c:1474
#59 0x0000563eb631a4d6 in command_loop_2 
(handlers=handlers@entry=0x90) at keyboard.c:1124
#60 0x0000563eb63aa9a1 in internal_catch (tag=tag@entry=0x10050, 
func=func@entry=0x563eb631a4b0 <command_loop_2>, arg=arg@entry=0x90) 
at eval.c:1197
#61 0x0000563eb631a471 in command_loop () at keyboard.c:1102
#62 0x0000563eb6321642 in recursive_edit_1 () at keyboard.c:711
#63 0x0000563eb63219d0 in Frecursive_edit () at keyboard.c:794
#64 0x0000563eb61eca5f in main (argc=1, argv=0x7ffce40e36d8) at 
emacs.c:2529

I tried using the "finish" gdb command from this point and here is 
what happened: -

(gdb) finish
Run till exit from #0  0x00007f11e8d139df in poll () from 
/usr/lib/libc.so.6
0x00007f11ec43726b in ?? () from /usr/lib/libxcb.so.1
(gdb) finish
Run till exit from #0  0x00007f11ec43726b in ?? () from 
/usr/lib/libxcb.so.1
0x00007f11ec438d1d in xcb_wait_for_event () from /usr/lib/libxcb.so.1
(gdb) finish
Run till exit from #0  0x00007f11ec438d1d in xcb_wait_for_event () 
from /usr/lib/libxcb.so.1
0x00007f11ec49ab09 in _XReadEvents () from /usr/lib/libX11.so.6
(gdb) finish
Run till exit from #0  0x00007f11ec49ab09 in _XReadEvents () from 
/usr/lib/libX11.so.6
0x00007f11ec48143a in XIfEvent () from /usr/lib/libX11.so.6
(gdb) finish
Run till exit from #0  0x00007f11ec48143a in XIfEvent () from 
/usr/lib/libX11.so.6

(at this point the "finish" command does not return).

I hope that helps. I will try to reproduce the problem while running 
in gdb and I will send an update if I'm successful.

Kind regards,

--
Simon Pugnet
https://www.polaris64.net/

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