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: <20150313223409.GE10954@cloud>
Date:	Fri, 13 Mar 2015 15:34:09 -0700
From:	josh@...htriplett.org
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Oleg Nesterov <oleg@...hat.com>, Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.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>,
	Thiago Macieira <thiago.macieira@...el.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	X86 ML <x86@...nel.org>
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task
 exit notification via fd

On Fri, Mar 13, 2015 at 03:28:26PM -0700, Andy Lutomirski wrote:
> On Fri, Mar 13, 2015 at 3:20 PM,  <josh@...htriplett.org> wrote:
> > On Fri, Mar 13, 2015 at 02:34:58PM -0700, Andy Lutomirski wrote:
> >> On Fri, Mar 13, 2015 at 12:57 PM,  <josh@...htriplett.org> wrote:
> >> > A process launching a new process with CLONE_FD is explicitly requesting
> >> > that the process be automatically reaped without any other process
> >> > having to wait on it.  The task needs to not become a zombie, because
> >> > otherwise, it'll show up in waitpid(-1, ...) calls in the parent
> >> > process, which would break the ability to use this to completely
> >> > encapsulate process management within a library and not interfere with
> >> > the parent's process handling via SIGCHLD and wait{pid,3,4}.
> >>
> >> Wouldn't the correct behavior be to keep it alive as a zombie but
> >> *not* show it in waitpid, etc?
> >
> > That's a significant change to the semantics of waitpid.  And then
> > someone would still need to wait on the process, which we'd like to
> > avoid.  (We don't want to have magic "reap on read(2)" semantics,
> > because among other things, what if we add a means in the future to get
> > an additional file descriptor corresponding to an existing process?)
> 
> Do we not already have a state "dead, successfully waited on by
> parent, but still around because ptraced"?  If not, shouldn't we?
> Isn't that what PTRACE_SEIZE does?  Or am I just confused?

I don't think that affects the task's exit_state though.

- Josh Triplett
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