Emacs 31: running commands that requires user input from message passing may break emacs

[blahgeek]

How to reproduce

1. Use newest master version of emacs
2. Create a large file (larger than large-file-warning-threshold)
3. Use vterm_cmd find-file to open the file

Expected behavior

The usual "really open large file?" prompt is shown and opens the file.

Actual behavior

Emacs becomes non-responsive forever. "C-g" or other keys does not work at all.

Backtrace

(gdb) bt
#0  pselect64_syscall
    (sigmask=<optimized out>, timeout=<optimized out>, exceptfds=0x0, writefds=0x7fffffff8d90, readfds=0x7fffffff8d10, nfds=23)
    at ../sysdeps/unix/sysv/linux/pselect.c:34
#1  __pselect
    (nfds=23, readfds=0x7fffffff8d10, writefds=0x7fffffff8d90, exceptfds=0x0, timeout=<optimized out>, sigmask=<optimized out>)
    at ../sysdeps/unix/sysv/linux/pselect.c:56
#2  0x00005555557d7a8c in really_call_select (arg=0x7fffffff8c00)
    at thread.c:624
#3  0x00005555557d870f in flush_stack_call_func
    (arg=0x7fffffff8c00, func=0x5555557d7a20 <really_call_select>)
    at lisp.h:4524
#4  thread_select
    (func=<optimized out>, max_fds=max_fds@entry=23, rfds=rfds@entry=0x7fffffff8d10, wfds=wfds@entry=0x7fffffff8d90, efds=efds@entry=0x0, timeout=timeout@entry=0x7fffffff9360, sigmask=0x0) at thread.c:656
#5  0x0000555555808968 in xg_select
    (fds_lim=23, rfds=rfds@entry=0x7fffffff94d0, wfds=wfds@entry=0x7fffffff9550, efds=efds@entry=0x0, timeout=timeout@entry=0x7fffffff9360, sigmask=sigmask@entry=0x0) at xgselect.c:205
#6  0x00005555557b2f8b in wait_reading_process_output
    (time_limit=time_limit@entry=0, nsecs=nsecs@entry=0, read_kbd=read_kbd@entry=-1, do_display=true, wait_for_cell=wait_for_cell@entry=0x0, wait_proc=wait_proc@entry=0x0, just_wait_proc=0) at process.c:5746
#7  0x00005555556d9ab4 in kbd_buffer_get_event
    (end_time=0x0, used_mouse_menu=0x0, kbp=<synthetic pointer>) at lisp.h:1178
#8  read_event_from_main_queue
    (used_mouse_menu=0x0, local_getcjmp=0x7fffffff9960, end_time=0x0)
    at keyboard.c:2325
#9  read_decoded_event_from_main_queue
    (used_mouse_menu=<optimized out>, prev_event=<optimized out>, local_getcjmp=<optimized out>, end_time=<optimized out>) at keyboard.c:2389
#10 read_char
    (commandflag=commandflag@entry=0, map=map@entry=0x0, prev_event=prev_event@entry=0x30, used_mouse_menu=used_mouse_menu@entry=0x0, end_time=0x0)
    at keyboard.c:3021
#11 0x0000555555781e3b in read_filtered_event
    (no_switch_frame=false, ascii_required=false, error_nonascii=false, input_method=<optimized out>, seconds=0x0) at lisp.h:1178
#12 0x00005555557550d0 in Ffuncall (nargs=1, args=0x7fffffff9dc0)
    at eval.c:3079
#13 0x00007fffedf7e94f in F726561642d6d756c7469706c652d63686f6963652d2d73686f72742d616e7377657273_read_multiple_choice__short_answers_0 ()
    at /tmp/squashfs-root/bin/../lib/emacs/31.0.50/native-lisp/31.0.50-0b45e146/preloaded/rmc-9c382b5d-8a589e38.eln
#14 0x00005555557550d0 in Ffuncall (nargs=5, args=0x7fffffff9e40)
    at eval.c:3079
#15 0x00007fffedf7e121 in F726561642d6d756c7469706c652d63686f696365_read_multiple_choice_0 ()
    at /tmp/squashfs-root/bin/../lib/emacs/31.0.50/native-lisp/31.0.50-0b45e146/preloaded/rmc-9c382b5d-8a589e38.eln
#16 0x00005555557550d0 in Ffuncall (nargs=4, args=0x7fffffff9f20)
    at eval.c:3079
#17 0x00007fffee4759c2 in F66696c65732d2d61736b2d757365722d61626f75742d6c617267652d66696c65_files__ask_user_about_large_file_0 ()
    at /tmp/squashfs-root/bin/../lib/emacs/31.0.50/native-lisp/31.0.50-0b45e146/preloaded/files-1e8937b2-a64d80f7.eln
#18 0x00005555557550d0 in Ffuncall (nargs=5, args=0x7fffffff9fd0)
    at eval.c:3079
#19 0x00007fffee475bab in F61626f72742d69662d66696c652d746f6f2d6c61726765_abort_if_file_too_large_0 ()
    at /tmp/squashfs-root/bin/../lib/emacs/31.0.50/native-lisp/31.0.50-0b45e146/preloaded/files-1e8937b2-a64d80f7.eln
#20 0x00005555557550d0 in Ffuncall (nargs=5, args=0x7fffffffa0c8)
    at eval.c:3079
#21 0x00007fffee476e75 in F66696e642d66696c652d6e6f73656c656374_find_file_noselect_0 ()
    at /tmp/squashfs-root/bin/../lib/emacs/31.0.50/native-lisp/31.0.50-0b45e146/preloaded/files-1e8937b2-a64d80f7.eln
#22 0x00005555557550d0 in Ffuncall (nargs=5, args=0x7fffffffa170)
    at eval.c:3079
#23 0x00007fffee47406f in F66696e642d66696c65_find_file_0 ()
    at /tmp/squashfs-root/bin/../lib/emacs/31.0.50/native-lisp/31.0.50-0b45e146/preloaded/files-1e8937b2-a64d80f7.eln
#24 0x000055555575874e in eval_sub (form=<optimized out>) at lisp.h:752
#25 0x000055555575a0e7 in internal_lisp_condition_case
    (var=0x2f19a20, bodyform=0x55555acf1de3, handlers=<optimized out>)
    at eval.c:1533
#26 0x0000555555758604 in eval_sub (form=<optimized out>) at lisp.h:752
#27 0x0000555555758c90 in Fprogn (body=<optimized out>) at eval.c:439
#28 funcall_lambda (fun=0x55555be3767d, nargs=1, arg_vector=0x7fffffffa4f8)
    at eval.c:3336
#29 0x00005555557550d0 in Ffuncall
    (nargs=nargs@entry=2, args=args@entry=0x7fffffffa4f0) at eval.c:3079
#30 0x0000555555755662 in Fapply (nargs=2, args=0x7fffffffa4f0) at eval.c:2708
#31 0x0000555555758491 in eval_sub (form=<optimized out>) at eval.c:2556
#32 0x0000555555758604 in eval_sub (form=<optimized out>) at lisp.h:752
#33 0x0000555555759c60 in Fprogn (body=<optimized out>) at eval.c:439
#34 FletX (args=0x555559e8a0e3) at eval.c:1042
#35 0x0000555555758604 in eval_sub (form=<optimized out>) at lisp.h:752
#36 0x0000555555759c60 in Fprogn (body=<optimized out>) at eval.c:439
#37 FletX (args=0x555559e8a043) at eval.c:1042
#38 0x0000555555758604 in eval_sub (form=<optimized out>) at lisp.h:752
#39 0x0000555555758c90 in Fprogn (body=<optimized out>) at eval.c:439
#40 funcall_lambda (fun=0x55555c20e525, nargs=1, arg_vector=0x7fffffffaa28)
    at eval.c:3336
#41 0x00005555557550d0 in Ffuncall
    (nargs=nargs@entry=2, args=args@entry=0x7fffffffaa20) at eval.c:3079
#42 0x0000555555755662 in Fapply (nargs=2, args=0x7fffffffaa20) at eval.c:2708
#43 0x00007fffce6f83bd in F767465726d2d2d6576616c_vterm__eval_0 ()
    at /home/yikai/.emacs.d/eln-cache/31.0.50-0b45e146/vterm-f27e86fd-309818c3.eln
#44 0x00005555557550d0 in Ffuncall
    (nargs=nargs@entry=2, args=args@entry=0x7fffffffaa90) at eval.c:3079
#45 0x000055555578e5b8 in module_funcall
    (env=0x7fffffffabd0, func=0x55555a9bae88, nargs=1, args=0x7fffffffab10)
    at emacs-module.c:679
#46 0x00007fffce6c285e in vterm_eval
    (env=env@entry=0x7fffffffabd0, string=<optimized out>)
    at /home/yikai/.emacs.d/lib/vterm/elisp.c:203
#47 0x00007fffce6bfbd9 in term_redraw
    (term=0x5555593667e0, env=env@entry=0x7fffffffabd0)
    at /home/yikai/.emacs.d/lib/vterm/vterm-module.c:637
#48 0x00007fffce6c003c in Fvterm_redraw
    (env=0x7fffffffabd0, nargs=<optimized out>, args=<optimized out>, data=<optimized out>) at /home/yikai/.emacs.d/lib/vterm/vterm-module.c:1340
#49 0x000055555578f30a in funcall_module
    (function=0x55555a9baf45, nargs=1, arglist=0x7fffffffbe48)
    at emacs-module.c:1296
#50 0x00005555557550d0 in Ffuncall
    (nargs=nargs@entry=2, args=args@entry=0x7fffffffbe40) at eval.c:3079
#51 0x0000555555755662 in Fapply (nargs=2, args=0x7fffffffbe40) at eval.c:2708
#52 0x0000555555758491 in eval_sub (form=<optimized out>) at eval.c:2556
#53 0x0000555555758604 in eval_sub (form=<optimized out>) at lisp.h:752
#54 0x0000555555758c90 in Fprogn (body=<optimized out>) at eval.c:439
#55 funcall_lambda (fun=0x55555ac5bd75, nargs=2, arg_vector=0x7fffffffc050)
    at eval.c:3336
#56 0x0000555555759649 in apply_lambda
    (fun=0x55555ac5bd75, args=<optimized out>, count=count@entry=...)
    at eval.c:3201
#57 0x0000555555758017 in eval_sub (form=<optimized out>) at eval.c:2673
#58 0x0000555555758c90 in Fprogn (body=<optimized out>) at eval.c:439
#59 funcall_lambda (fun=0x55555ac5bda5, nargs=2, arg_vector=0x7fffed1ff048)
    at eval.c:3336
#60 0x00005555557550d0 in Ffuncall
    (nargs=nargs@entry=3, args=args@entry=0x7fffed1ff040) at eval.c:3079
#61 0x0000555555755662 in Fapply (nargs=3, args=0x7fffed1ff040) at eval.c:2708
#62 0x000055555579cdd2 in exec_byte_code
    (fun=<optimized out>, args_template=<optimized out>, nargs=<optimized out>, args=<optimized out>) at lisp.h:752
#63 0x00005555557550d0 in Ffuncall (nargs=2, args=0x7fffffffc3d0)
    at eval.c:3079
#64 0x00007fffce6f6561 in F767465726d2d2d64656c617965642d726564726177_vterm__delayed_redraw_0 ()
    at /home/yikai/.emacs.d/eln-cache/31.0.50-0b45e146/vterm-f27e86fd-309818c3.eln
#65 0x00005555557550d0 in Ffuncall
    (nargs=nargs@entry=2, args=args@entry=0x7fffffffc520) at eval.c:3079
#66 0x0000555555755662 in Fapply (nargs=2, args=0x7fffffffc520) at eval.c:2708
#67 0x00005555557550d0 in Ffuncall (nargs=3, args=0x7fffffffc518)
    at eval.c:3079
#68 0x00007fffee19bfc8 in F74696d65722d6576656e742d68616e646c6572_timer_event_handler_0 ()
    at /tmp/squashfs-root/bin/../lib/emacs/31.0.50/native-lisp/31.0.50-0b45e146/preloaded/timer-3ee7cfd9-4017b895.eln
#69 0x00005555557550d0 in Ffuncall
    (nargs=nargs@entry=2, args=args@entry=0x7fffffffc600) at eval.c:3079
#70 0x00005555556d45d9 in timer_check_2
    (idle_timers=<optimized out>, timers=0x55555ba52bc3) at lisp.h:1178
#71 timer_check () at keyboard.c:4870
#72 0x00005555556d48f5 in readable_events (flags=flags@entry=1)
    at keyboard.c:3602
#73 0x00005555556d4b28 in get_input_pending (flags=flags@entry=1)
    at keyboard.c:7873
#74 0x00005555556d7e38 in detect_input_pending_run_timers
    (do_display=do_display@entry=true) at keyboard.c:11577
#75 0x00005555557b2a1c in wait_reading_process_output
    (time_limit=time_limit@entry=0, nsecs=nsecs@entry=0, read_kbd=read_kbd@entry=-1, do_display=true, wait_for_cell=wait_for_cell@entry=0x0, wait_proc=wait_proc@entry=0x0, just_wait_proc=0) at process.c:5842
#76 0x00005555556d9ab4 in kbd_buffer_get_event
    (end_time=0x0, used_mouse_menu=0x7fffffffd1cb, kbp=<synthetic pointer>)
    at lisp.h:1178
#77 read_event_from_main_queue
    (used_mouse_menu=0x7fffffffd1cb, local_getcjmp=0x7fffffffcde0, end_time=0x0)
 at keyboard.c:2325
#78 read_decoded_event_from_main_queue
    (used_mouse_menu=<optimized out>, prev_event=<optimized out>, local_getcjmp=
<optimized out>, end_time=<optimized out>) at keyboard.c:2389
#79 read_char
    (commandflag=1, map=0x55555ba53963, prev_event=0x0, used_mouse_menu=0x7fffff
ffd1cb, end_time=0x0) at keyboard.c:3021
#80 0x00005555556dbbb4 in read_key_sequence
    (keybuf=0x7fffffffd340, prompt=0x0, dont_downcase_last=<optimized out>, can_
return_switch_frame=true, fix_current_buffer=true, prevent_redisplay=<optimized 
out>, disable_text_conversion_p=false) at keyboard.c:10747
#81 0x00005555556dd48f in command_loop_1 () at lisp.h:1178
#82 0x0000555555753a52 in internal_condition_case
    (bfun=bfun@entry=0x5555556dd2c0 <command_loop_1>, handlers=handlers@entry=0x
90, hfun=hfun@entry=0x5555556d1e70 <cmd_error>) at eval.c:1607
#83 0x00005555556ca852 in command_loop_2 (handlers=handlers@entry=0x90)
    at keyboard.c:1163
#84 0x0000555555753981 in internal_catch
    (tag=tag@entry=0x12390, func=func@entry=0x5555556ca830 <command_loop_2>, arg
=arg@entry=0x90) at eval.c:1286
#85 0x00005555556ca7ee in command_loop () at lisp.h:1178
#86 0x00005555556d19e6 in recursive_edit_1 () at keyboard.c:749
#87 0x00005555556d1d94 in Frecursive_edit () at keyboard.c:832
#88 0x00005555555aa88d in main (argc=<optimized out>, argv=<optimized out>)
    at emacs.c:2625

Possible fix

Running commands directly during redraw (which is during reading process outputs) seems flaky. I think we should use (run-with-timer 0 ...) to defer the command execution. I can confirm that using run-with-timer can fix the issue.