linux-kernel - Re: [PATCH] sched: fix another race when reading /proc/sched

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Message-Id: <20081215105053.89263708.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Mon, 15 Dec 2008 10:50:53 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Paul Menage <menage@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] sched: fix another race when reading /proc/sched_debug

On Mon, 15 Dec 2008 09:39:18 +0800
Li Zefan <lizf@...fujitsu.com> wrote:

> Paul Menage wrote:
> > I sent out some patches last week (search for hierarchy_mutex) that would
> > mean that you'd only need to take a subsystem-local lock to keep a cgroup
> > alive. People seemed to like them so I'll tweak them based on feedback and
> > send them on to Andrew.
> > 
> 
> Unfortunately, AFAICS the proposed hierarchy_mutex can't solve this bug. :(
> 
Hmm ? how about this way if cgroup->dentry is problem ?

at creation:
  - cpu_cgroup_populate() should record "tg" that "this cgroup has valid dentry"
at deletion
  - css_tryget() will be useful to avoid the race.

thx,
-Kame

> > Paul
> > 
> > On Dec 14, 2008 4:48 AM, "Peter Zijlstra" <a.p.zijlstra@...llo.nl> wrote:
> > 
> > On Sun, 2008-12-14 at 10:54 +0800, Li Zefan wrote: > > i merged it up in
> > tip/master, could you pleas...
> > Can't we detect a dead task-group and skip those instead of adding this
> > global lock?
> > 
> >> Signed-off-by: Li Zefan <lizf@...fujitsu.com> > --- > kernel/sched_fair.c
> > | 6 ++++++ > kerne...
> > 
> 
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