Re: [PATCH bpf-next 13/15] mm, memcg: Add new helper get_obj_cgroup_from_cgroup

[Yafang Shao <laoar.shao@gmail.com>]

On Sat, Aug 13, 2022 at 12:57 AM Shakeel Butt <shakeelb@google.com> 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.
>
> Can you please add couple of lines on why you need objcg?
>

Sure. will update in the next version.

> >
> > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > ---
> >  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;
> > +}
> > +
> > +struct obj_cgroup *get_obj_cgroup_from_cgroup(struct cgroup *cgrp)
> > +{
> > +     struct cgroup_subsys_state *css;
> > +     struct mem_cgroup *memcg;
> > +     struct obj_cgroup *objcg;
> > +
> > +     rcu_read_lock();
> > +     css = rcu_dereference(cgrp->subsys[memory_cgrp_id]);
> > +     if (!css || !css_tryget_online(css)) {
> > +             rcu_read_unlock();
> > +             cgroup_put(cgrp);
> > +             return ERR_PTR(-EINVAL);
> > +     }
> > +     rcu_read_unlock();
> > +     cgroup_put(cgrp);
>
> The above put seems out of place and buggy.
>

Thanks for pointing it out.
The cgroup_put should be used in bpf_map_save_memcg().
I will update it.

-- 
Regards
Yafang