linux-kernel - Re: [PATCH v2 5/7] clone4: Add a CLONE_AUTOREAP flag to automatically reap the child process

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Date:	Sun, 15 Mar 2015 15:52:23 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Kees Cook <keescook@...omium.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@...or.com>, Rik van Riel <riel@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Thiago Macieira <thiago.macieira@...el.com>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH v2 5/7] clone4: Add a CLONE_AUTOREAP flag to
	automatically reap the child process

On 03/15, Josh Triplett wrote:
>
> Add a CLONE_AUTOREAP flag to request this behavior unconditionally,

Yes, CLONE_AUTOREAP is much better. And I agree (mostly) with that
we should rely on do_notify_parent().

Howver the patch still doesn't look right. First of all, ->autoreap
should be per-process, not per-thread. And there are ptrace/mt issues,
it seems. Just for example, we should avoid EXIT_TRACE if autoreap in
wait_task_zombie() even if we are going to re-notify parent.

Yes... and other problems with ptrace. So let me nack this patch for
the moment ;) But let me repeat that personally I agree with this
change "in general".

EXCEPT: do we really want SIGCHLD from the exiting child? I think we
do not. I won't really argue though, but this should be discussed and
documented. IIUC, with your patch it is still sent.

Josh, please give me some time to think and re-check, I'll write another
email next week. I am not sure this is really needed, but it seems to
me that we need the preparation patch to make this change clear/simple.

Oleg.

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