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

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH 3/3] mm: memcontrol: add sanity checks for memcg->id.ref on get/put
Date	2016-08-03 00:00 +0200
Message-ID	<s1PTb-1PI-1@gated-at.bofh.it> (permalink)
References	<s1HiX-4uK-63@gated-at.bofh.it> <s1HiX-4uK-65@gated-at.bofh.it> <s1HiX-4uK-61@gated-at.bofh.it>
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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

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Re: [PATCH 3/3] mm: memcontrol: add sanity checks for memcg->id.ref  on get/put Michal Hocko <mhocko@kernel.org> - 2016-08-02 14:50 +0200
  Re: [PATCH 3/3] mm: memcontrol: add sanity checks for memcg->id.ref  on get/put Michal Hocko <mhocko@kernel.org> - 2016-08-03 00:00 +0200

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