From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit
 notification via fd
Date: Fri, 13 Mar 2015 15:28:26 -0700
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To: Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>
Cc: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Al Viro <viro-RmSDqhL/yNMiFSDQTTA3OLVCufUGDwFn@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@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>, Thiago Macieira <thiago.macieira-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>, Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Linux FS Devel <linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, X86 ML <x86-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
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On Fri, Mar 13, 2015 at 3:20 PM,  <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org> wrote:
> On Fri, Mar 13, 2015 at 02:34:58PM -0700, Andy Lutomirski wrote:
>> On Fri, Mar 13, 2015 at 12:57 PM,  <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org> wrote:
>> > A process launching a new process with CLONE_FD is explicitly requesting
>> > that the process be automatically reaped without any other process
>> > having to wait on it.  The task needs to not become a zombie, because
>> > otherwise, it'll show up in waitpid(-1, ...) calls in the parent
>> > process, which would break the ability to use this to completely
>> > encapsulate process management within a library and not interfere with
>> > the parent's process handling via SIGCHLD and wait{pid,3,4}.
>>
>> Wouldn't the correct behavior be to keep it alive as a zombie but
>> *not* show it in waitpid, etc?
>
> That's a significant change to the semantics of waitpid.  And then
> someone would still need to wait on the process, which we'd like to
> avoid.  (We don't want to have magic "reap on read(2)" semantics,
> because among other things, what if we add a means in the future to get
> an additional file descriptor corresponding to an existing process?)
>

Do we not already have a state "dead, successfully waited on by
parent, but still around because ptraced"?  If not, shouldn't we?
Isn't that what PTRACE_SEIZE does?  Or am I just confused?

--Andy