linux-kernel - Re: [2.6.27.24] Kernel coredump to a pipe is failing

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Message-ID: <20090527190513.GA32452@redhat.com>
Date:	Wed, 27 May 2009 21:05:13 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	paul@...-scientist.net, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [2.6.27.24] Kernel coredump to a pipe is failing

On 05/27, Andi Kleen wrote:
>
> > Actually, I think there is a strong reason to handle signals during
> > core dumping. The coredump can take a lot of time/resources, not good
> > it looks like unkillable procees to users.
>
> One problem with that is if you send a process a string of signals that cause
> a core dump and then kill. In the old case you would just get a full core dump
> on the first signal and be done. With your change it would process
> the second signal too and stop the dumping and you get none or a partial
> core dump. That might well break existing setups.

I don't think we should worry about this particular case. Suppose a user
does

	kill(pid, SIGQUIT);
	kill(pid, SIGKILL);

In this case, most likely the core dump will not start. Because SIGKILL
will set SIGNAL_GROUP_EXIT before the process dequeues SIGQUIT and start
do_coredump() which checks signal_group_exit() in zap_threads().

But yes, I agree, this change is user-visible and should be discussed.

Oleg.

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