linux-kernel - Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd

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Message-ID: <20150314203029.GA11656@redhat.com>
Date:	Sat, 14 Mar 2015 21:30:29 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	Thiago Macieira <thiago.macieira@...el.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	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>,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task
	exit notification via fd

On 03/14, Josh Triplett wrote:
>
> What I was proposing was that a task that isn't yet dead, but that is
> going to be autoreaped, is not eligible for waiting either.  All the
> various wait* familiy of system calls should pretend it doesn't exist at
> all, because returning an autoreaped task from a wait* call introduces a
> race condition if the parent tries to *do* anything with the returned
> PID.  If you launch a process with CLONE_FD, you need to manage it
> exclusively with that fd, not with the wait* family of system calls.
>
> That also implies that the child-stop and child-continued mechanisms
> (do_notify_parent_cldstop, WSTOPPED, WCONTINUED) should ignore the task
> too.  In the future there could be a flag to clone4 that lets you get
> stop and continue notifications through the file descriptor.

So far I strongly disagree, and I think that "autoreap" feature should
not depend on CLONE_FD.

However, as I already said, perhaps something like W_IGNORE_AUTOREAP
for wait* makes sense.

Plus we should also discuss the reparenting. Ok, let me leave this
discussion until I read 0/4 at least.

Oleg.

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