Re: dialog --pause not timing out on serial console (dialog 1.2)

[Stefan Puiu]

Hi Thomas,

On Wed, Jul 14, 2021 at 11:37 PM Thomas Dickey <dickey@his.com> wrote:
[...]
> > Somebody managed to reproduce this again, and this time I debugged
> > dialog a bit with gdb, and it seems to be stuck inside a tcsetattr
> > call:
> >
> > (gdb) bt
> > #0  0x0000003b96aeb5cc in __GI_tcsetattr (fd=1,
> > optional_actions=optional_actions@entry=1,
> >     termios_p=termios_p@entry=0x7fff17feba40) at
> > ../sysdeps/unix/sysv/linux/tcsetattr.c:83
> > #1  0x0000003b98e1677a in _nc_set_tty_mode
> > (buf=buf@entry=0x7fff17feba40) at
> > ../../ncurses/tinfo/lib_ttyflags.c:108
> > #2  0x0000003b98e10d8c in cbreak () at ../../ncurses/tinfo/lib_raw.c:155
> > #3  0x0000003b97214f33 in _nc_initscr () at 
> > ../../ncurses/base/lib_newterm.c:79
>
> hmm - ncurses kind of expects the system to return an error :-)
>
> perhaps the serial I/O driver isn't that cooperative.
>
> If that happened often enough, I'd have some code to do a sanity check
> on "tty" to make sure the initialization wouldn't hang.

This hang doesn't seem to reproduce consistently, unfortunately. As
far as I can tell, most times dialog runs fine. Also, even when it
hangs, hooking up the serial console through software unblocks it. Is
there a way to find what is the serial driver used here? It would've
been good to have tried to print hung tasks using the magic sysrq key,
but it didn't occur to me to do that while the problem was reproduced.

>
> > #4  newterm (name=<optimized out>, ofp=<optimized out>, ifp=<optimized
> > out>) at ../../ncurses/base/lib_newterm.c:332
> > #5  0x0000003b97211343 in initscr () at ../../ncurses/base/lib_initscr.c:87
> > #6  0x0000003e24225f5d in init_dialog (input=<optimized out>,
> > output=0x3b96db81c0 <_IO_2_1_stderr_>) at util.c:385
> > #7  0x0000000000402351 in main (argc=12, argv=0x7fff17fec638) at 
> > dialog.c:1844
> >
> > (gdb) info locals
> > resultvar = 18446744073709551104
> > k_termios = {c_iflag = 21504, c_oflag = 5, c_cflag = 7346, c_lflag =
> > 2105, c_line = 0 '\000',
> >   c_cc = 
> > "\003\034\177\025\004\000\001\000\021\023\032\000\022\017\027\026\000\000"}
> > cmd = <optimized out>
> > retval = <optimized out>
> >
> >
> > As far as I can tell, it's trying to call ioctl 0x5043 (TCSETSW) on fd
> > 1 (stdout), and that call blocks. Maybe the serial driver in the
> > kernel is getting blocked on something? Any ideas?
>
> ncurses asked isatty if stdout is a tty (and was told that it is),
> so it tries using termios stuff to initialize it -- and apparently
> gets nowhere

Sigh. Thanks for helping me make sense of this.

Stefan.