bug#48476: Bug#988581: emacs-gtk: Emacs hangs with 100% cpu if started within a current directory that has a name ending with ".tar"

[Robert Pluim]

>>>>> On Mon, 17 May 2021 16:42:33 +0200, Lars Ingebrigtsen <larsi@gnus.org> 
>>>>> said:

    Lars> Rob Browning <rlb@defaultvalue.org> writes:
    >>> My emacs get stuck with 100% cpu when started from a directory ending 
with
    >>> ".tar".
    >>> 
    >>> For example, the following commands trigger the error:
    >>> - mkdir test.tar
    >>> - cd test.tar
    >>> - emacs

    Lars> I can reproduce this on Debian/bullseye on the trunk, too -- Emacs 
uses
    Lars> 100% CPU and can't be interrupted with `C-g'.

    Lars> strace seems to say that it's inflooping like this:

    Lars> pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.so.gz", O_RDONLY|O_CLOEXEC) 
= -1 ENOENT (No such file or directory)
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.elc", O_RDONLY|O_CLOEXEC) = 
15
    Lars> [pid 70536] fstat(15, {st_mode=S_IFREG|0644, st_size=24503, ...}) = 0
    Lars> [pid 70536] read(15, ";ELC\33\0\0\0\n;;; Compiled\n;;; in Ema"..., 
512) = 512
    Lars> [pid 70536] lseek(15, 0, SEEK_SET)      = 0
    Lars> [pid 70536] newfstatat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.elc", 
{st_mode=S_IFREG|0644, st_size=24503, ...}, 0) = 0
    Lars> [pid 70536] newfstatat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.el", {st_mode=S_IFREG|0644, 
st_size=28504, ...}, 0) = 0
    Lars> [pid 70536] fcntl(15, F_GETFL)          = 0x8000 (flags 
O_RDONLY|O_LARGEFILE)
    Lars> [pid 70536] fstat(15, {st_mode=S_IFREG|0644, st_size=24503, ...}) = 0
    Lars> [pid 70536] read(15, ";ELC\33\0\0\0\n;;; Compiled\n;;; in Ema"..., 
4096) = 4096
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.so", O_RDONLY|O_CLOEXEC) = 
-1 ENOENT (No such file or directory)
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.so.gz", O_RDONLY|O_CLOEXEC) 
= -1 ENOENT (No such file or directory)
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.elc", O_RDONLY|O_CLOEXEC) = 
16
    Lars> [pid 70536] fstat(16, {st_mode=S_IFREG|0644, st_size=24503, ...}) = 0
    Lars> [pid 70536] read(16, ";ELC\33\0\0\0\n;;; Compiled\n;;; in Ema"..., 
512) = 512
    Lars> [pid 70536] lseek(16, 0, SEEK_SET)      = 0
    Lars> [pid 70536] newfstatat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.el", {st_mode=S_IFREG|0644, 
st_size=28504, ...}, 0) = 0
    Lars> [pid 70536] fcntl(16, F_GETFL)          = 0x8000 (flags 
O_RDONLY|O_LARGEFILE)
    Lars> [pid 70536] fstat(16, {st_mode=S_IFREG|0644, st_size=24503, ...}) = 0
    Lars> [pid 70536] read(16, ";ELC\33\0\0\0\n;;; Compiled\n;;; in Ema"..., 
4096) = 4096
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.so", O_RDONLY|O_CLOEXEC) = 
-1 ENOENT (No such file or directory)
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.so.gz", O_RDONLY|O_CLOEXEC) 
= -1 ENOENT (No such file or directory)
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.elc", O_RDONLY|O_CLOEXEC) = 
17
    Lars> [pid 70536] fstat(17, {st_mode=S_IFREG|0644, st_size=24503, ...}) = 0
    Lars> [pid 70536] close(17)                   = 0
    Lars> [pid 70536] close(16)                   = 0
    Lars> [pid 70536] close(15)                   = 0
    Lars> [pid 70536] close(14)                   = 0
    Lars> [pid 70536] close(13)                   = 0
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.so", O_RDONLY|O_CLOEXEC) = 
-1 ENOENT (No such file or directory)
    Lars> [pid 70536] openat(AT_FDCWD, 
"/home/larsi/src/emacs/trunk/lisp/net/tramp-archive.so.gz", O_RDONLY|O_CLOEXEC) 
= -1 ENOENT (No such file or directory)

I have a backtrace from gdb that might shed some light.

Michael, this is emacs signalling an error for a recursive load,
apparently forever. master has the same issue. I set a breakpoint at
lread.c:1366

  {
    int load_count = 0;
    Lisp_Object tem = Vloads_in_progress;
    FOR_EACH_TAIL_SAFE (tem)
      if (!NILP (Fequal (found, XCAR (tem))) && (++load_count > 3))
->      signal_error ("Recursive load", Fcons (found, Vloads_in_progress));
    record_unwind_protect (record_load_unwind, Vloads_in_progress);
    Vloads_in_progress = Fcons (found, Vloads_in_progress);
  }

and got this backtrace, which implicates
'tramp-archive-autoload-file-name-handler'

Thread 1 "emacs" hit Breakpoint 5, Fload (file=XIL(0x555556847f74), 
noerror=XIL(0), nomessage=XIL(0x30), nosuffix=<optimized out>, 
    must_suffix=<optimized out>) at lread.c:1366
1366            signal_error ("Recursive load", Fcons (found, 
Vloads_in_progress));
(gdb) bt
#0  Fload (file=XIL(0x555556847f74), noerror=XIL(0), nomessage=XIL(0x30), 
nosuffix=<optimized out>, must_suffix=<optimized out>)
    at lread.c:1366
#1  0x000055555572be5a in save_match_data_load
    (file=XIL(0x555556847f74), noerror=noerror@entry=XIL(0), 
nomessage=nomessage@entry=XIL(0x30), nosuffix=nosuffix@entry=XIL(0), 
must_suffix=must_suffix@entry=XIL(0x30)) at lread.c:1616
#2  0x0000555555702881 in Fautoload_do_load (fundef=XIL(0x55555677e753), 
funname=XIL(0xbc9bd0), macro_only=XIL(0)) at eval.c:2308
#3  0x0000555555702af2 in Ffuncall (nargs=4, args=0x7fffffff92c0) at lisp.h:1002
#4  0x0000555555702d04 in call3 (fn=<optimized out>, arg1=<optimized out>, 
arg2=<optimized out>, arg3=<optimized out>) at eval.c:2910
#5  0x00005555556b8d76 in Fexpand_file_name (name=XIL(0x55555649d1c4), 
default_directory=<optimized out>) at fileio.c:905
#6  0x000055555572ab71 in readevalloop
    (readcharfun=XIL(0x7770), infile0=0x7fffffff9500, 
sourcename=XIL(0x55555649d1c4), printflag=false, unibyte=XIL(0), 
readfun=XIL(0), start=<optimized out>, end=XIL(0)) at lisp.h:1002
#7  0x000055555572bbb1 in Fload
    (file=<optimized out>, noerror=XIL(0), nomessage=XIL(0x30), 
nosuffix=<optimized out>, must_suffix=<optimized out>) at lisp.h:1002
#8  0x000055555572be5a in save_match_data_load
    (file=XIL(0x555556847f74), noerror=noerror@entry=XIL(0), 
nomessage=nomessage@entry=XIL(0x30), nosuffix=nosuffix@entry=XIL(0), 
must_suffix=must_suffix@entry=XIL(0x30)) at lread.c:1616
#9  0x0000555555702881 in Fautoload_do_load (fundef=XIL(0x55555677e753), 
funname=XIL(0xbc9bd0), macro_only=XIL(0)) at eval.c:2308
#10 0x0000555555702af2 in Ffuncall (nargs=4, args=0x7fffffff96b0) at lisp.h:1002
#11 0x0000555555702d04 in call3 (fn=<optimized out>, arg1=<optimized out>, 
arg2=<optimized out>, arg3=<optimized out>) at eval.c:2910
#12 0x00005555556b8d76 in Fexpand_file_name (name=XIL(0x55555649cff4), 
default_directory=<optimized out>) at fileio.c:905
#13 0x000055555572ab71 in readevalloop
    (readcharfun=XIL(0x7770), infile0=0x7fffffff98f0, 
sourcename=XIL(0x55555649cff4), printflag=false, unibyte=XIL(0), 
readfun=XIL(0), start=<optimized out>, end=XIL(0)) at lisp.h:1002
#14 0x000055555572bbb1 in Fload
    (file=<optimized out>, noerror=XIL(0), nomessage=XIL(0x30), 
nosuffix=<optimized out>, must_suffix=<optimized out>) at lisp.h:1002
#15 0x000055555572be5a in save_match_data_load
    (file=XIL(0x555556847f74), noerror=noerror@entry=XIL(0), 
nomessage=nomessage@entry=XIL(0x30), nosuffix=nosuffix@entry=XIL(0), 
must_suffix=must_suffix@entry=XIL(0x30)) at lread.c:1616
#16 0x0000555555702881 in Fautoload_do_load (fundef=XIL(0x55555677e753), 
funname=XIL(0xbc9bd0), macro_only=XIL(0)) at eval.c:2308
#17 0x0000555555702af2 in Ffuncall (nargs=4, args=0x7fffffff9aa0) at lisp.h:1002
#18 0x0000555555702d04 in call3 (fn=<optimized out>, arg1=<optimized out>, 
arg2=<optimized out>, arg3=<optimized out>) at eval.c:2910
#19 0x00005555556b8d76 in Fexpand_file_name (name=XIL(0x55555649ce74), 
default_directory=<optimized out>) at fileio.c:905
#20 0x000055555572ab71 in readevalloop
    (readcharfun=XIL(0x7770), infile0=0x7fffffff9ce0, 
sourcename=XIL(0x55555649ce74), printflag=false, unibyte=XIL(0), 
readfun=XIL(0), start=<optimized out>, end=XIL(0)) at lisp.h:1002
#21 0x000055555572bbb1 in Fload
    (file=<optimized out>, noerror=XIL(0), nomessage=XIL(0x30), 
nosuffix=<optimized out>, must_suffix=<optimized out>) at lisp.h:1002
#22 0x000055555572be5a in save_match_data_load
    (file=XIL(0x555556847f74), noerror=noerror@entry=XIL(0), 
nomessage=nomessage@entry=XIL(0x30), nosuffix=nosuffix@entry=XIL(0), 
must_suffix=must_suffix@entry=XIL(0x30)) at lread.c:1616
#23 0x0000555555702881 in Fautoload_do_load (fundef=XIL(0x55555677e753), 
funname=XIL(0xbc9bd0), macro_only=XIL(0)) at eval.c:2308
#24 0x0000555555702af2 in Ffuncall (nargs=4, args=0x7fffffff9e90) at lisp.h:1002
#25 0x0000555555702d04 in call3 (fn=<optimized out>, arg1=<optimized out>, 
arg2=<optimized out>, arg3=<optimized out>) at eval.c:2910
#26 0x00005555556b8d76 in Fexpand_file_name (name=XIL(0x5555568573e4), 
default_directory=<optimized out>) at fileio.c:905
#27 0x000055555572ab71 in readevalloop
    (readcharfun=XIL(0x7770), infile0=0x7fffffffa0d0, 
sourcename=XIL(0x5555568573e4), printflag=false, unibyte=XIL(0), 
readfun=XIL(0), start=<optimized out>, end=XIL(0)) at lisp.h:1002
#28 0x000055555572bbb1 in Fload
    (file=<optimized out>, noerror=XIL(0), nomessage=XIL(0x30), 
nosuffix=<optimized out>, must_suffix=<optimized out>) at lisp.h:1002
#29 0x000055555572be5a in save_match_data_load
    (file=XIL(0x555556847f74), noerror=noerror@entry=XIL(0), 
nomessage=nomessage@entry=XIL(0x30), nosuffix=nosuffix@entry=XIL(0), 
must_suffix=must_suffix@entry=XIL(0x30)) at lread.c:1616
#30 0x0000555555702881 in Fautoload_do_load (fundef=XIL(0x55555677e753), 
funname=XIL(0xbc9bd0), macro_only=XIL(0)) at eval.c:2308
#31 0x0000555555702af2 in Ffuncall (nargs=5, args=0x7fffffffa2a8) at lisp.h:1002
#32 0x000055555573df98 in exec_byte_code
    (bytestr=<optimized out>, vector=<optimized out>, maxdepth=<optimized out>, 
args_template=<optimized out>, nargs=<optimized out>, args=<optimized out>) at 
bytecode.c:632
#33 0x0000555555702b37 in Ffuncall (nargs=4, args=0x7fffffffa580) at eval.c:3052
#34 0x00005555557049f8 in Fapply (nargs=2, args=0x7fffffffa610) at eval.c:2666
#35 0x00005555557052fc in eval_sub (form=<optimized out>) at lisp.h:731
#36 0x0000555555705ca5 in Fprogn (body=XIL(0)) at eval.c:471
#37 funcall_lambda (fun=<optimized out>, nargs=4, arg_vector=0x7fffffffa7d0) at 
eval.c:3313
#38 0x0000555555702b37 in Ffuncall (nargs=5, args=0x7fffffffa7c8) at eval.c:3052
#39 0x000055555573df98 in exec_byte_code
    (bytestr=<optimized out>, vector=<optimized out>, maxdepth=<optimized out>, 
args_template=<optimized out>, nargs=<optimized out>, args=<optimized out>) at 
bytecode.c:632
#40 0x0000555555702b37 in Ffuncall (nargs=2, args=0x7fffffffaaa0) at eval.c:3052
#41 0x0000555555702caa in call1 (fn=<optimized out>, 
arg1=arg1@entry=XIL(0x555555caf184)) at eval.c:2896
#42 0x00005555555d9b17 in decode_mode_spec (string=<synthetic pointer>, 
field_width=1, c=<optimized out>, w=<optimized out>)
    at xdisp.c:26947
#43 display_mode_element
    (it=<optimized out>, depth=<optimized out>, field_width=<optimized out>, 
precision=<optimized out>, elt=<optimized out>, props=XIL(0), risky=<optimized 
out>) at xdisp.c:25855
#44 0x00005555555d98b2 in display_mode_element
    (it=0x7fffffffadd0, depth=3, field_width=0, precision=-5, elt=<optimized 
out>, props=XIL(0), risky=<optimized out>) at lisp.h:719
#45 0x00005555555d98b2 in display_mode_element
    (it=0x7fffffffadd0, depth=1, field_width=0, precision=0, elt=<optimized 
out>, props=XIL(0), risky=<optimized out>) at lisp.h:719
#46 0x00005555555db1a4 in display_mode_line (w=w@entry=0x55555602f120, 
face_id=<optimized out>, format=XIL(0x7ffff1c35e2b))
    at lisp.h:1002
#47 0x00005555555db3ce in display_mode_lines (w=w@entry=0x55555602f120) at 
xdisp.c:25415
#48 0x00005555555db613 in redisplay_mode_lines (window=XIL(0x55555602f125), 
force=force@entry=false) at xdisp.c:25351
#49 0x00005555555e68fb in echo_area_display (update_frame_p=<optimized out>) at 
xdisp.c:12289
#50 0x00005555555e6a59 in message3_nolog (m=<optimized out>) at xdisp.c:11232
#51 0x00005555555e6cc8 in message3 (m=m@entry=XIL(0x555556034f54)) at 
xdisp.c:11162
#52 0x00005555556f9df0 in Fmessage (args=0x7fffffffc350, nargs=<optimized out>) 
at editfns.c:2875
#53 Fmessage (nargs=<optimized out>, args=0x7fffffffc350) at editfns.c:2843
#54 0x0000555555702bfb in Ffuncall (nargs=3, args=0x7fffffffc348) at eval.c:3036
#55 0x000055555573df98 in exec_byte_code
    (bytestr=<optimized out>, vector=<optimized out>, maxdepth=<optimized out>, 
args_template=<optimized out>, nargs=<optimized out>, args=<optimized out>) at 
bytecode.c:632
#56 0x0000555555702b37 in Ffuncall (nargs=1, args=0x7fffffffc690) at eval.c:3052
#57 0x000055555573df98 in exec_byte_code
    (bytestr=<optimized out>, vector=<optimized out>, maxdepth=<optimized out>, 
args_template=<optimized out>, nargs=<optimized out>, args=<optimized out>) at 
bytecode.c:632
#58 0x0000555555702b37 in Ffuncall (nargs=2, args=0x7fffffffce68) at eval.c:3052
#59 0x000055555573df98 in exec_byte_code
    (bytestr=<optimized out>, vector=<optimized out>, maxdepth=<optimized out>, 
args_template=<optimized out>, nargs=<optimized out>, args=<optimized out>) at 
bytecode.c:632
#60 0x0000555555702b37 in Ffuncall (nargs=1, args=0x7fffffffd730) at eval.c:3052
#61 0x000055555573df98 in exec_byte_code
    (bytestr=<optimized out>, vector=<optimized out>, maxdepth=<optimized out>, 
args_template=<optimized out>, nargs=<optimized out>, args=<optimized out>) at 
bytecode.c:632
#62 0x0000555555705e5f in apply_lambda (fun=XIL(0x7ffff1bc6d85), 
args=<optimized out>, count=4) at eval.c:3185
#63 0x0000555555704ee3 in eval_sub (form=<optimized out>) at eval.c:2588
#64 0x0000555555706b09 in Feval (form=XIL(0x7ffff20f0e2b), lexical=<optimized 
out>) at eval.c:2340
#65 0x0000555555701bd7 in internal_condition_case
    (bfun=bfun@entry=0x555555687050 <top_level_2>, 
handlers=handlers@entry=XIL(0x90), hfun=hfun@entry=0x55555568c860 <cmd_error>)
    at eval.c:1475
#66 0x0000555555687cc6 in top_level_1 (ignore=ignore@entry=XIL(0)) at 
keyboard.c:1111
#67 0x00005555557040d3 in internal_catch (tag=tag@entry=XIL(0xe4c0), 
func=func@entry=0x555555687ca0 <top_level_1>, arg=arg@entry=XIL(0))
    at eval.c:1198
#68 0x0000555555686fd8 in command_loop () at lisp.h:1002
#69 0x000055555568c476 in recursive_edit_1 () at keyboard.c:720
#70 0x000055555568c7a2 in Frecursive_edit () at keyboard.c:789
#71 0x00005555555a2cda in main (argc=2, argv=<optimized out>) at emacs.c:2297

Lisp Backtrace:
"tramp-archive-file-name-handler" (0xffff92c8)
"tramp-archive-file-name-handler" (0xffff96b8)
"tramp-archive-file-name-handler" (0xffff9aa8)
"tramp-archive-file-name-handler" (0xffff9e98)
"tramp-archive-file-name-handler" (0xffffa2b0)
"file-remote-p" (0xffffa588)
"apply" (0xffffa610)
"tramp-archive-autoload-file-name-handler" (0xffffa7d0)
"file-remote-p" (0xffffaaa8)
"message" (0xffffc350)
"display-startup-echo-area-message" (0xffffc698)
"command-line-1" (0xffffce70)
"command-line" (0xffffd738)
"normal-top-level" (0xffffdc00)
(gdb) 

Robert
--