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

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Message-ID: <20150323150329.GA31561@cloud>
Date:	Mon, 23 Mar 2015 08:03:29 -0700
From:	josh@...htriplett.org
To:	David Drysdale <drysdale@...gle.com>
Cc:	Thiago Macieira <thiago.macieira@...el.com>,
	Kees Cook <keescook@...omium.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 Mon, Mar 23, 2015 at 02:12:34PM +0000, David Drysdale wrote:
> On Mon, Mar 16, 2015 at 11:29 PM,  <josh@...htriplett.org> wrote:
> > On Mon, Mar 16, 2015 at 03:14:14PM -0700, Thiago Macieira wrote:
> >> 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.
> >
> > Minor nit: CLONE_AUTOREAP makes the process autoreap and nobody can wait
> > on it, but if you pass SIGCHLD or some other exit signal to clone then
> > you'll still get that signal.
> 
> Quick query: does CLONE_AUTOREAP also affect waiting for non-exit
> events (i.e. WUNTRACED / WCONTINUED), by original parent and/or ptracer?

It shouldn't, no.  You can't wait on the process to exit (you'll get
-ECHLD after it wakes up), but you can wait on it to continue or
similar; none of the autoreap changes should affect that.

- Josh Triplett
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