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Date:   Thu, 6 Dec 2018 18:29:32 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Enke Chen <enkechen@cisco.com>, Dave Martin <Dave.Martin@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Arnd Bergmann <arnd@arndb.de>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Khalid Aziz <khalid.aziz@oracle.com>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Helge Deller <deller@gmx.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
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        Catalin Marinas <Catalin.Marinas@arm.com>,
        Will Deacon <Will.Deacon@arm.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
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        Marcos Paulo de Souza <marcos.souza.org@gmail.com>,
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        "Victor Kamensky (kamensky)" <kamensky@cisco.com>,
        "xe-linux-external@cisco.com" <xe-linux-external@cisco.com>,
        Stefan Strogin <sstrogin@cisco.com>
Subject: Re: [PATCH v5 1/2] kernel/signal: Signal-based pre-coredump
 notification
Message-ID: <20181206172931.GA12967@redhat.com>
References: <7741efa7-a3f8-62a1-ba52-613883164643@cisco.com>
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 <20181026082812.GA10581@redhat.com>
 <21f678a8-4001-df36-c26e-e96cf203b1b1@cisco.com>
 <20181029111804.GA24820@redhat.com>
 <0c197608-3b7e-ffd1-8943-801a60beb917@cisco.com>
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 <20181128151911.GN3505@e103592.cambridge.arm.com>
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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.