linux-kernel - Re: [PATCH 1/8] signal: Make SIGKILL during coredumps an explicit special case

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Date:   Tue, 11 Jan 2022 11:28:01 -0600
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Olivier Langlois <olivier@...llion01.com>
Cc:     Heiko Carstens <hca@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "<linux-arch@...r.kernel.org>" <linux-arch@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Alexey Gladkov <legion@...nel.org>,
        Kyle Huey <me@...ehuey.com>, Oleg Nesterov <oleg@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>
Subject: Re: [PATCH 1/8] signal: Make SIGKILL during coredumps an explicit
 special case

Olivier Langlois <olivier@...llion01.com> writes:

> On Mon, 2022-01-10 at 15:11 -0600, Eric W. Biederman wrote:
>> 
>> 
>> I have been able to confirm that changing wait_event_interruptible to
>> wait_event_killable was the culprit.  Something about the way
>> systemd-coredump handles coredumps is not compatible with
>> wait_event_killable.
>
> This is my experience too that systemd-coredump is doing something
> unexpected. When I tested the patch:
> https://lore.kernel.org/lkml/cover.1629655338.git.olivier@trillion01.com/
>
> to make sure that the patch worked, sending coredumps to systemd-
> coredump was making systemd-coredump, well, core dump... Not very
> useful...

Oh.  Wow....

> Sending the dumps through a pipe to anything else than systemd-coredump
> was working fine.

Interesting.

I need to read through the pipe code and see how all of that works.  For
writing directly to disk only ignoring killable interruptions are the
usual semantics.  Ordinary pipe code has different semantics, and I
suspect that is what is tripping things up.

As for systemd-coredump it does whatever it does and I suspect some
versions of systemd-coredump are simply not robust if a coredump stops
unexpectedly.

The good news is the pipe code is simple enough, it will be possible to
completely read through that code.

Eric