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From: Roland McGrath <roland@redhat.com>
To: Oleg Nesterov <oleg@tv-sign.ru>
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Cc: linux-kernel@vger.kernel.org, "Eric W. Biederman" <ebiederm@xmission.com>,
       Ingo Molnar <mingo@elte.hu>, "Paul E. McKenney" <paulmck@us.ibm.com>,
       Andrew Morton <akpm@osdl.org>, Lee Revell <rlrevell@joe-job.com>
Subject: Re: [PATCH rc1-mm 2/3] coredump: shutdown current process first
In-Reply-To: Oleg Nesterov's message of  Sunday, 9 April 2006 04:11:27 +0400 <20060409001127.GA101@oleg>
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Date: Mon, 10 Apr 2006 00:08:40 -0700 (PDT)
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> This patch optimize zap_threads() for the case when there are
> no ->mm users except the current's thread group. In that case
> we can avoid 'for_each_process()' loop.

This is a very good optimization.  Please don't use a goto here when a
simple if block and some reindenting works just fine.

I would be inclined to restructure the inner loop something like this:

		p = g;
		while (unlikely(p->mm == NULL)) {
			p = next_thread(p);
			if (p == g)
				break;
		}
		if (p->mm == mm) {
			/*
			 * p->sighand can't disappear, but
			 * may be changed by de_thread()
			 */
			lock_task_sighand(p, &flags);
			zap_process(p);
			unlock_task_sighand(p, &flags);
		}

But that is just taste.

> It also adds a useful invariant: SIGNAL_GROUP_EXIT (if checked
> under ->siglock) always implies that all threads (except may be
> current) have pending SIGKILL.

I agree that's a sensible thing to be able to rely on (though I don't know
of a practical difference it makes atm).  If this is merged with by
SIGNAL_GROUP_EXEC change, then the invariant is that SIGNAL_GROUP_EXIT
always means that all threads (including current) either have pending
SIGKILL or are already calling do_group_exit/do_exit.


Thanks,
Roland