Re: dash behaviour, was Re: core dump analysis

[Geert Uytterhoeven <geert@linux-m68k.org>]

Hi Finn,

On Sat, Apr 8, 2023 at 7:26 AM Finn Thain <fthain@linux-m68k.org> wrote:
> On Fri, 7 Apr 2023, Geert Uytterhoeven wrote:
> > > The only way I have found to alter dash's inclination to crash is to
> > > reboot. (I said previously I was unable to reproduce this in a single
> > > user mode shell but it turned out to be more subtle.)
> >
> > That sounds like memory corruption somewhere else, e.g. in the buffer
> > cache...
> >
>
> If so, once the corruption showed up, you would expect the same crash next
> time...
>
> root@debian:~# sh /etc/init.d/mountdevsubfs.sh start
> *** stack smashing detected ***: terminated
> Aborted (core dumped)
> root@debian:~# sh /etc/init.d/mountdevsubfs.sh start
> *** stack smashing detected ***: terminated
> Aborted (core dumped)
> *** stack smashing detected ***: terminated
> Aborted (core dumped)
> root@debian:~# sh /etc/init.d/mountdevsubfs.sh start
> *** stack smashing detected ***: terminated
> Aborted (core dumped)
> root@debian:~# echo 3 > /proc/sys/vm/drop_caches
> [  937.250000] bash (717): drop_caches: 3
> root@debian:~# sh /etc/init.d/mountdevsubfs.sh start
> root@debian:~# sh /etc/init.d/mountdevsubfs.sh start
> *** stack smashing detected ***: terminated
> Aborted (core dumped)
> root@debian:~# sh /etc/init.d/mountdevsubfs.sh start
> *** stack smashing detected ***: terminated
> Aborted (core dumped)
> *** stack smashing detected ***: terminated
> Aborted (core dumped)
>
> I'd say it's probably not buffer cache corruption causing this because we
> can see two subshells fail, then just one.

OK.

> For that build I enabled SLUB_DEBUG but forgot to enable SLUB_DEBUG_ON --

FWIW, unfortunately not all SL*B_DEBUG are equal. I've seen
memory corruptions that were identified by SLAB_DEBUG, but not by
the other allocators.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds