linux-kernel - Re: [RFC][PATCH] ps command race fix take 4 [1/4] callback subroutine

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Message-Id: <20060905104156.3a91e941.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 5 Sep 2006 10:41:56 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	ebiederm@...ssion.com (Eric W. Biederman)
Cc:	linux-kernel@...r.kernel.org, akpm@...l.org, ak@...e.de
Subject: Re: [RFC][PATCH] ps command race fix take 4 [1/4] callback
 subroutine

On Mon, 04 Sep 2006 16:48:43 -0600
ebiederm@...ssion.com (Eric W. Biederman) wrote:

> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> writes:
> 
> > Updated some dirty codes. maybe easier to read than previous one.
> >
> > This ps command fix (proc_pid_readdir() fix) fixes the problem by
> >
> > - attach a callback for updating pointer from file descriptor to a task invoked
> >   at release_task()
> > - no additional global lock is required.
> > - walk through all and only task structs which is thread group leader.
> >
> > *Bad* point is adding additonal (small) lock and callback in exit path.
> With an unbounded callback chain length influenced by user space.
> 
yes. 1000 ps process will add 1000 chains. 1000 callbacks are called if a task is
removed while 1000 ps task points to it.


-Kame

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