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

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Date:	Tue, 16 Dec 2008 10:35:09 -0800
From:	Paul Menage <menage@...gle.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH] sched: fix another race when reading /proc/sched_debug

On Tue, Dec 16, 2008 at 4:55 AM, Li Zefan <lizf@...fujitsu.com> wrote:
>
> This avoids accessing a destroyed cgroup, but still race with cgroup_create.
> You sugguested call cgroup_create_dir() before calling subsystems' create()
> method.
>

I think that if we need a fix for 2.6.28 I'll just make cgroup_path()
check for a NULL dentry in the passed cgroup, rather than shuffling
any code around. That combined with a simple RCU free in
cgroup_diput() should do the trick - I think I'll leave the existing
synchronize_rcu() at the beginning of cgroup_diput() in case we need
it for more reasons than I originally mentioned in the comment there.

Paul
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