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

From: Josh Triplett <josh@joshtriplett.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Thiago Macieira <thiago.macieira@intel.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@amacapital.net>,
	Ingo Molnar <mingo@redhat.com>, Kees Cook <keescook@chromium.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	"H. Peter Anvin" <hpa@zytor.com>, Rik van Riel <riel@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Michael Kerrisk <mtk.manpages@gmail.com>,
	linux-kernel@vger.kernel.org, linux-api@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task exit notification via fd
Date: Sat, 14 Mar 2015 15:14:18 -0700	[thread overview]
Message-ID: <20150314221417.GK22130@thin> (raw)
In-Reply-To: <20150314203029.GA11656@redhat.com>

On Sat, Mar 14, 2015 at 09:30:29PM +0100, Oleg Nesterov wrote:
> 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.

After reading your other mail and thinking about this, I agree that the
two can be separated; see my othermail for the details.

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

I think you can safely wait for v2 of the last patch, though the first
four patches should be almost completely identical in v2.

- Josh Triplett