On Tue, Aug 13, 2024 at 08:47:11PM GMT, Kinsey Ho <kinseyho@xxxxxxxxxx> wrote:
> --- a/include/linux/cgroup-defs.h
> +++ b/include/linux/cgroup-defs.h
> @@ -172,7 +172,11 @@ struct cgroup_subsys_state {
> /* reference count - access via css_[try]get() and css_put() */
> struct percpu_ref refcnt;
>
> - /* siblings list anchored at the parent's ->children */
> + /*
> + * siblings list anchored at the parent's ->children
> + *
> + * linkage is protected by cgroup_mutex or RCU
> + */
> struct list_head sibling;
> struct list_head children;
Thanks, this is good.
>
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 0a97cb2ef124..ece2316e2bca 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -4602,8 +4602,9 @@ struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
> *
> * While this function requires cgroup_mutex or RCU read locking, it
> * doesn't require the whole traversal to be contained in a single critical
> - * section. This function will return the correct next descendant as long
> - * as both @pos and @root are accessible and @pos is a descendant of @root.
> + * section. Additionally, it isn't necessary to hold onto a reference to @pos.
> + * This function will return the correct next descendant as long as both @pos
> + * and @root are accessible and @pos is a descendant of @root.
> *
> * If a subsystem synchronizes ->css_online() and the start of iteration, a
> * css which finished ->css_online() is guaranteed to be visible in the
> @@ -4651,8 +4652,9 @@ EXPORT_SYMBOL_GPL(css_next_descendant_pre);
> *
> * While this function requires cgroup_mutex or RCU read locking, it
> * doesn't require the whole traversal to be contained in a single critical
> - * section. This function will return the correct rightmost descendant as
> - * long as @pos is accessible.
> + * section. Additionally, it isn't necessary to hold onto a reference to @pos.
> + * This function will return the correct rightmost descendant as long as @pos
> + * is accessible.
> */
> struct cgroup_subsys_state *
> css_rightmost_descendant(struct cgroup_subsys_state *pos)
> @@ -4696,9 +4698,9 @@ css_leftmost_descendant(struct cgroup_subsys_state *pos)
> *
> * While this function requires cgroup_mutex or RCU read locking, it
> * doesn't require the whole traversal to be contained in a single critical
> - * section. This function will return the correct next descendant as long
> - * as both @pos and @cgroup are accessible and @pos is a descendant of
> - * @cgroup.
> + * section. Additionally, it isn't necessary to hold onto a reference to @pos.
> + * This function will return the correct next descendant as long as both @pos
> + * and @cgroup are accessible and @pos is a descendant of @cgroup.
> *
> * If a subsystem synchronizes ->css_online() and the start of iteration, a
> * css which finished ->css_online() is guaranteed to be visible in the
I'd say these comments are unnecessary given the functions have
cgroup_assert_mutex_or_rcu_locked() but if it helps overall
understanding in broader context, why not.
Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx>
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