linux-kernel - Re: [PATCH v5 1/2] kernel/signal: Signal-based pre-coredump notification

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Date:   Thu, 6 Dec 2018 18:29:32 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Enke Chen <enkechen@...co.com>, Dave Martin <Dave.Martin@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Khalid Aziz <khalid.aziz@...cle.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Helge Deller <deller@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian@...uner.io>,
        Catalin Marinas <Catalin.Marinas@....com>,
        Will Deacon <Will.Deacon@....com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Rik van Riel <riel@...riel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Roman Gushchin <guro@...com>,
        Marcos Paulo de Souza <marcos.souza.org@...il.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "Victor Kamensky (kamensky)" <kamensky@...co.com>,
        "xe-linux-external@...co.com" <xe-linux-external@...co.com>,
        Stefan Strogin <sstrogin@...co.com>
Subject: Re: [PATCH v5 1/2] kernel/signal: Signal-based pre-coredump
 notification

On 12/04, Andrew Morton wrote:
>
> I'm not sure what to make of this patchset, really.  Oleg sounds
> unhappy and that's always a bad sign.  And signals are rather ugly
> things.  Oleg, can you please expand on your concerns?

I don't really know what can I say...

Yes the signals are ugly things, this is one reason. Worse, you need to
use real-time predump_signal if parent has 2 or more children.

And when it comes to child-parent notifications we already have do_wait().
So probably it would be better to implement WCOREDUMP so that the parent
could rely on SIGCHLD + waitpid(WCOREDUMP). Not that I think this is a
good idea and this is much more complex especially if we want to report
this event to ptracer too, while this patch is very simple.

In fact I think that we need something more generic, but I can't suggest
any good idea :/

May be we could simply add a tracepoint or perf_event_coredump, I dunno.
Sure, the usage of perf events is not that simple...

Oleg.