linux-kernel - Re: [PATCH] cgroup: Convert synchronize_rcu to call_rcu in cgroup_attach

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Message-ID: <AANLkTikhE-z7HuLimuj_pJLKd7FHq+w6PQCd85XuT0a8@mail.gmail.com>
Date:	Wed, 24 Nov 2010 10:58:23 -0800
From:	Paul Menage <menage@...gle.com>
To:	Li Zefan <lizf@...fujitsu.com>
Cc:	Colin Cross <ccross@...roid.com>, linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org
Subject: Re: [PATCH] cgroup: Convert synchronize_rcu to call_rcu in cgroup_attach_task

On Tue, Nov 23, 2010 at 6:06 PM, Li Zefan <lizf@...fujitsu.com> wrote:
>
> If we do this, it's not anymore safe to use get_css_set(), which just
> increments the refcount without checking if it's zero.

I don't believe that it's currently safe to use get_css_set() on a
zero-refcount css_set anyway - a css_set starts with refcount 1 and
can be freed the moment that its refcount reaches 0. You can only use
get_css_set() on a stable reference to an existing css_set, which by
definition has a refcount of at least 1. Were you thinking of any
particular existing uses?

Paul
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