On Wed, Aug 10, 2022 at 03:18:38PM +0000, Yafang Shao wrote:
> Introduce new helper get_obj_cgroup_from_cgroup() to get obj_cgroup from
> a specific cgroup.
>
> Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
> ---
> include/linux/memcontrol.h | 1 +
> mm/memcontrol.c | 41 +++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 42 insertions(+)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index 2f0a611..901a921 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1713,6 +1713,7 @@ static inline void set_shrinker_bit(struct mem_cgroup *memcg,
> int __memcg_kmem_charge_page(struct page *page, gfp_t gfp, int order);
> void __memcg_kmem_uncharge_page(struct page *page, int order);
>
> +struct obj_cgroup *get_obj_cgroup_from_cgroup(struct cgroup *cgrp);
> struct obj_cgroup *get_obj_cgroup_from_current(void);
> struct obj_cgroup *get_obj_cgroup_from_page(struct page *page);
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 618c366..762cffa 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2908,6 +2908,47 @@ static struct obj_cgroup *__get_obj_cgroup_from_memcg(struct mem_cgroup *memcg)
> return objcg;
> }
>
> +static struct obj_cgroup *get_obj_cgroup_from_memcg(struct mem_cgroup *memcg)
> +{
> + struct obj_cgroup *objcg;
> +
> + if (memcg_kmem_bypass())
> + return NULL;
> +
> + rcu_read_lock();
> + objcg = __get_obj_cgroup_from_memcg(memcg);
> + rcu_read_unlock();
> + return objcg;
This code doesn't make sense to me. What does rcu read lock protect here?
