linux-kernel - Re: [PATCH] cgroups: remove rcu_read_lock() in cgroupstats

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Message-ID: <6599ad830811241241p2a01c7e1h163766c088141468@mail.gmail.com>
Date:	Mon, 24 Nov 2008 12:41:09 -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>
Subject: Re: [PATCH] cgroups: remove rcu_read_lock() in cgroupstats_build()

On Fri, Nov 21, 2008 at 8:09 PM, Lai Jiangshan <laijs@...fujitsu.com> wrote:
>
> cgroup_iter_* do not need rcu_read_lock().
>
> In cgroup_enable_task_cg_lists(), do_each_thread() and
> while_each_thread() are protected by RCU,
> it's OK, for write_lock(&css_set_lock) implies rcu_read_lock() in non-RT kernel.
>
> If we need explicit rcu_read_lock(), we should add rcu_read_lock()
> in cgroup_enable_task_cg_lists(), not cgroup_iter_*.
>
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>

Acked-by: Paul Menage <menage@...gle.com>

Seems reasonable. Thanks,

Paul

> ---
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 358e775..e6d92a5 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -2047,7 +2047,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
>
>        ret = 0;
>        cgrp = dentry->d_fsdata;
> -       rcu_read_lock();
>
>        cgroup_iter_start(cgrp, &it);
>        while ((tsk = cgroup_iter_next(cgrp, &it))) {
> @@ -2072,7 +2071,6 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
>        }
>        cgroup_iter_end(cgrp, &it);
>
> -       rcu_read_unlock();
>  err:
>        return ret;
>  }
>
>
>
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