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

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Message-Id: <20090701074654.A6C6321D57@magilla.sf.frob.com>
Date:	Wed,  1 Jul 2009 00:46:54 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc:	Oleg Nesterov <oleg@...hat.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

> 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.

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.


Thanks,
Roland
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