linux-kernel - Re: [PATCH v2 5/7] clone4: Add a CLONE_AUTOREAP flag to automatically reap the child process

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Message-ID: <20150320211055.GA13125@cloud>
Date:	Fri, 20 Mar 2015 14:10:55 -0700
From:	josh@...htriplett.org
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Thiago Macieira <thiago.macieira@...el.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.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>,
	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 v2 5/7] clone4: Add a CLONE_AUTOREAP flag to
 automatically reap the child process

On Fri, Mar 20, 2015 at 08:09:14PM +0100, Oleg Nesterov wrote:
> On 03/20, Thiago Macieira wrote:
> >
> > On Friday 20 March 2015 19:14:04 Oleg Nesterov wrote:
> > > Also. I forgot that the kernel always resets ->exit_signal to SIGCHLD on
> > > exec or reparenting. Reparenting is probably fine. But what about exec?
> > > Should it keep ->exit_signal == 0 if "autoreap" ? I think it should not, to
> > > avoid the strange special case.
> >
> > Not delivering any signal was the objective of this patch series, so yes
> > exit_signal == 0 should survive an exec and even re-exec.
> 
> OK, but then perhaps we should never send SIGCHLD (on exit) if "autoreap",
> to make the logic simple.
> 
> And copy_process() should probably do
> 
> 	if ((clone_flags & CSIGNAL) && (clone_flags && CLONE_AUTOREAP))
> 		return -EINVAL;
> 
> so that we still can change this behaviour later.

I'm fine with that, as it would handle the particular use case we care
about.

However, the reset-signal-on-reparent thing might still make sense,
particularly for the ptrace-reparent case (less so for the
reparent-to-child-reaper case).

- Josh Triplett
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