Re: [PATCH 04/14] device_cgroup: remove direct access to cgroup->children

Serge E. Hallyn
2014-05-14T12:52:58Z

Quoting Tejun Heo (tj@kernel.org):
> Currently, devcg::has_children() directly tests cgroup->children for
> list emptiness. The field is not a published field and scheduled to
> go away. In addition, the test isn't strictly correct as devcg should
> only care about children which are visible to userland.
>
> This patch converts has_children() to use css_next_child() instead.
> The subtle incorrectness is noted and will be dealt with later.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Aristeu Rozanski <aris@redhat.com>
> Cc: Serge Hallyn <serge.hallyn@ubuntu.com>

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>

> ---
> security/device_cgroup.c | 12 ++++++++++--
> 1 file changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/security/device_cgroup.c b/security/device_cgroup.c
> index 3116015..75b4b18 100644
> --- a/security/device_cgroup.c
> +++ b/security/device_cgroup.c
> @@ -477,9 +477,17 @@ static int propagate_exception(struct dev_cgroup *devcg_root,
>
> static inline bool has_children(struct dev_cgroup *devcgroup)
> {
> - struct cgroup *cgrp = devcgroup->css.cgroup;
> + bool ret;
>
> - return !list_empty(&cgrp->children);
> + /*
> + * FIXME: There may be lingering offline csses and this function
> + * may return %true when there isn't any userland-visible child
> + * which is incorrect for our purposes.
> + */
> + rcu_read_lock();
> + ret = css_next_child(NULL, &devcgroup->css);
> + rcu_read_unlock();
> + return ret;
> }
>
> /*
> --
> 1.9.0
>
> --
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