linux-kernel - Re: [PATCH] cpuset: rcu_read_lock() to protect task_cs() even we don't dereference to task

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Message-ID: <6599ad830811211105p711aebc3v85ffffbc399bdd6e@mail.gmail.com>
Date:	Fri, 21 Nov 2008 11:05:18 -0800
From:	Paul Menage <menage@...gle.com>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH] cpuset: rcu_read_lock() to protect task_cs() even we 
	don't dereference to task_cs()'s return value

On Fri, Nov 21, 2008 at 12:49 AM, Lai Jiangshan <laijs@...fujitsu.com> wrote:
>
> task_cs() calls cgroup_subsys_state().

You man "calls task_subsys_state()"

>
> we must use rcu_read_lock() to protect cgroup_subsys_state().
>
> in current_cpuset_is_being_rebound(), we don't dereference to task_cs()'s
> return value, but task_cs() accesses css_set, this css_set maybe freed
> when task_cs() called.

Wouldn't this be fixed by your patch that adds an rcu_read_lock() to
task_subsys_state() ?

Paul

>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> ---
> diff --git a/kernel/cpuset.c b/kernel/cpuset.c
> index 3e00526..e0e087e 100644
> --- a/kernel/cpuset.c
> +++ b/kernel/cpuset.c
> @@ -1141,7 +1136,11 @@ done:
>
>  int current_cpuset_is_being_rebound(void)
>  {
> -       return task_cs(current) == cpuset_being_rebound;
> +       struct cpuset *cs;
> +       rcu_read_lock();
> +       cs = task_cs(current);
> +       rcu_read_unlock();
> +       return cs == cpuset_being_rebound;
>  }
>
>  static int update_relax_domain_level(struct cpuset *cs, s64 val)
>
>
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