On Fri, Aug 12, 2022 at 12:16 AM Roman Gushchin
<roman.gushchin@xxxxxxxxx> wrote:
>
> 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?
To protect rcu_dereference(memcg->objcg);.
Doesn't it need the read rcu lock ?
--
Regards
Yafang
