linux-kernel - Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for child processes

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Message-Id: <20100203172006.D3B2.A69D9226@jp.fujitsu.com>
Date:	Wed,  3 Feb 2010 17:24:23 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Lennart Poettering <lennart@...ttering.net>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] exit: PR_SET_ANCHOR for marking processes as reapers for child processes

> [ I already sent this patch half a year ago or so, as an RFC. I didn't
> really get any comments back then, however I am still interested in
> seeing this patch in the kernel tree. So here I go again: please
> comment! I have updated the patch to apply to the current upstream git
> master. ]
> 
> Right now, if a process dies all its children are reparented to init.
> This logic has good uses, i.e. for double forking when daemonizing.
> However it also allows child processes to "escape" their parents, which
> is a problem for software like session managers (such as gnome-session)
> or other process supervisors.

I think you need to explain why this patch improve gnome-session.

 - What's happen on current gnome-session. and When?
 - After the patch, Which behavior will be changed?
 - Why do you think gnome-session can ignore old kernel?
 - etc..

We don't have any input for judgement and advise.



> 
> This patch adds a simple flag for each process that marks it as an
> "anchor" process for all its children and grandchildren. If a child of
> such an anchor dies all its children will not be reparented to init, but
> instead to this anchor, escaping this anchor process is not possible. A
> task with this flag set hence acts is little "sub-init".
> 
> Anchors are fully recursive: if an anchor dies, all its children are
> reparented to next higher anchor in the process tree.
> 
> This is orthogonal to PID namespaces. PID namespaces virtualize the
> actual IDs in addition to introducing "sub-inits". This patch introduces
> "sub-inits" inside the same PID namespace.
> 
> This patch is compile tested only. It's relatively trivial, and is
> written in ignorance of the expected locking logic for accessing
> task_struct->parent. This mail is primarily intended as a request for
> comments. So please, I'd be happy about any comments!


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