linux-kernel - Re: [PATCH v2 0/7] CLONE_FD: Task exit notification via file descriptor

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Message-ID: <2381173.VxaIO6vGG3@tjmaciei-mobl4>
Date:	Mon, 16 Mar 2015 15:14:14 -0700
From:	Thiago Macieira <thiago.macieira@...el.com>
To:	Kees Cook <keescook@...omium.org>
Cc:	Josh Triplett <josh@...htriplett.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"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>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v2 0/7] CLONE_FD: Task exit notification via file descriptor

On Monday 16 March 2015 14:44:20 Kees Cook wrote:
> >               O_CLOEXEC
> >                      Set  the  close-on-exec  flag on the new file
> >descriptor. See the description of the O_CLOEXEC flag in open(2)  for
> >reasons why this may be useful.
> 
> This begs the question: what happens when all CLONE_FD fds for a
> process are closed? Will the parent get SIGCHLD instead, will it
> auto-reap, or will it be un-wait-able (I assume not this...)

Depends on CLONE_AUTOREAP. If it's on, then no one gets SIGCHLD, no one can 
wait() on it and the process autoreaps itself.

If it's no active, then the old rules apply: parent gets SIGCHILD and can 
wait(). If the parent exited first, then the child gets reparented to init, 
which can do the wait().

A child without CLONE_AUTOREAP should be wait()able. If it gets wait()ed 
before the clonefd is read, the clonefd() will return a 0 read. If it gets 
read before wait, then wait() reaps another child or returns -ECHILD. That's 
no different than two threads doing simultaneous wait() on the same child.
-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center

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