From mboxrd@z Thu Jan  1 00:00:00 1970
From: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task
	exit notification via fd
Date: Sat, 14 Mar 2015 20:18:36 +0100
Message-ID: <20150314191836.GA8416@redhat.com>
References: <cover.1426180120.git.josh@joshtriplett.org> <20150314141414.GA11062@redhat.com> <20150314143235.GA12086@redhat.com> <28025621.k7WkrfHd4d@tjmaciei-mobl4> <20150314190132.GB22130@thin>
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Cc: Thiago Macieira <thiago.macieira-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>,
	Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>,
	Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
	"Paul E. McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>,
	"H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>, Rik van Riel <riel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>,
	Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org
To: Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>
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On 03/14, Josh Triplett wrote:
>
> On Sat, Mar 14, 2015 at 11:38:29AM -0700, Thiago Macieira wrote:
> > On Saturday 14 March 2015 15:32:35 Oleg Nesterov wrote:
> > > It is not clear to me what do_wait() should do with ->autoreap child, even
> > > ignoring ptrace.
> > >
> > > Just suppose that real_parent has a single "autoreap" child. Should
> > > wait(NULL) hanf then?
> >
> > It should ignore the child that is set to autoreap. wait(NULL) should return -
> > ECHILD, indicating there are no children waiting to be reaped.
>
> Right.  And I don't think the current code does this.  I think we need
> to change wait_consider_task to early-return for ->autoreap just as it
> does for task_state == EXIT_DEAD.

No. This EXIT_DEAD is absolutely different. And this is another indication
that you might use it wrongly ;)

What we actually want is BUG_ON(task_state == EXIT_DEAD) here. We do not
want the EXIT_DEAD tasks in ->children/ptraced lists. These EXIT_DEAD tasks
complicate the exit/wait/reparent paths.

However, currently this is TODO. The main problem is the locking in
wait_task_zombie(), we can set EXIT_DEAD and remove the task from list
under read_lock().

And please see another email from me. So far  I disagree that wait(NULL)
should return ECHILD unconditionally. At least unless this is discussed
separately.

Oleg.