[Devel] Re: [PATCH v3 16/28] memcg: kmem controller charge/uncharge infrastructure

[Frederic Weisbecker]

On Wed, May 30, 2012 at 05:37:57PM +0400, Glauber Costa wrote:
> On 05/30/2012 05:37 PM, Frederic Weisbecker wrote:
> >Right. __mem_cgroup_get_kmem_cache() fetches the memcg of the owner
> >and calls memcg_create_cache_enqueue() which does css_tryget(&memcg->css).
> >After this tryget I think you're fine. And in-between you're safe against
> >css_set removal due to rcu_read_lock().
> >
> >I'm less clear with __mem_cgroup_new_kmem_page() though...
> 
> That one does not get memcg->css but it does call mem_cgroup_get(),
> that does prevent against the memcg structure being freed, which I
> believe to be good enough.

What if the owner calls cgroup_exit() between mem_cgroup_from_task()
and mem_cgroup_get()? The css_set which contains the memcg gets freed.
Also the reference on the memcg doesn't even prevent the css_set to
be removed, does it?