Re: [PATCH 2/5] cgroup: Fix an RCU warning in alloc_css_id()

Paul E. McKenney
2010-04-22T19:56:08Z

On Thu, Apr 22, 2010 at 05:30:00PM +0800, Li Zefan wrote:
> With CONFIG_PROVE_RCU=y, a warning can be triggered:
>
> # mount -t cgroup -o memory xxx /mnt
> # mkdir /mnt/0
>
> ...
> kernel/cgroup.c:4442 invoked rcu_dereference_check() without protection!
> ...
>
> This is a false-positive. It's safe to directly access parent_css->id.

Also queued for 2.6.34, thank you!

Thanx, Paul

> Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
> ---
> kernel/cgroup.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 4ca928d..3a53c77 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -4561,13 +4561,13 @@ static int alloc_css_id(struct cgroup_subsys *ss, struct cgroup *parent,
> {
> int subsys_id, i, depth = 0;
> struct cgroup_subsys_state *parent_css, *child_css;
> - struct css_id *child_id, *parent_id = NULL;
> + struct css_id *child_id, *parent_id;
>
> subsys_id = ss->subsys_id;
> parent_css = parent->subsys[subsys_id];
> child_css = child->subsys[subsys_id];
> - depth = css_depth(parent_css) + 1;
> parent_id = parent_css->id;
> + depth = parent_id->depth;
>
> child_id = get_new_cssid(ss, depth);
> if (IS_ERR(child_id))
> --
> 1.6.3
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.tux.org/lkml/