Re: [PATCH 3/3] mm: memcontrol: add sanity checks for memcg->id.ref on get/put

[Michal Hocko]

On Tue 02-08-16 14:45:03, Michal Hocko wrote:
> On Mon 01-08-16 16:26:26, Vladimir Davydov wrote:
> [...]
> >  static struct mem_cgroup *mem_cgroup_id_get_active(struct mem_cgroup *memcg)
> >  {
> > -	while (!atomic_inc_not_zero(&memcg->id.ref))
> > +	while (!atomic_inc_not_zero(&memcg->id.ref)) {
> > +		VM_BUG_ON(mem_cgroup_is_root(memcg));
> >  		memcg = parent_mem_cgroup(memcg);
> > +	}
> 
> why is this BUG_ON ok? What if the root.use_hierarchy=true?

Scratch that. I got it. root will never get its count down to 0. Sorry
about the noise.
-- 
Michal Hocko
SUSE Labs