linux-kernel - Re: [RFC][PATCH] Disable CLONE

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Date:	Wed, 1 Jul 2009 10:24:52 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oren Laadan <orenl@...columbia.edu>, serue@...ibm.com,
	Alexey Dobriyan <adobriyan@...il.com>,
	Containers <containers@...ts.linux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] Disable CLONE_PARENT for init

On 07/01, Roland McGrath wrote:
>
> > When global or container-init processes use CLONE_PARENT, they create a
> > multi-rooted process tree. 
>
> I take this to be the real motivation for your change.
> But you don't mention it in the code comment.
>
> > +	 * Swapper process sets the handler for SIGCHLD to SIG_DFL. If init
> > +	 * creates a sibling and the sibling exits, the SIGCHLD is sent to
> > +	 * the swapper (since the swapper's handler for SIGCHLD is SIG_DFL).
> > +	 * But since the swapper does not reap its children, the zombie will
> > +	 * remain forever. So prevent init from using CLONE_PARENT.
>
> This would be fixed by having swapper set its SIGCHLD to SIG_IGN instead,
> so such children self-reap.  That seems like the better fix for that.

This won't fix the problem. The child won't autoreap itself if ->exit_signal
!= SIGCHLD.

> If you want to make this change because of container-init issues, I think
> you should just say so independent of this global-init case.

Yes, agreed, the comment looks confusing.

Oleg

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