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Date:   Fri, 13 Apr 2018 10:55:53 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Kirill Tkhai <ktkhai@virtuozzo.com>
Cc:     akpm@linux-foundation.org, hannes@cmpxchg.org,
        vdavydov.dev@gmail.com, cgroups@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on
 mem_cgroup_css_alloc() failure
Message-ID: <20180413085553.GF17484@dhcp22.suse.cz>
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On Thu 12-04-18 17:52:04, Kirill Tkhai wrote:
[...]
> @@ -4471,6 +4477,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
>  
>  	return &memcg->css;
>  fail:
> +	mem_cgroup_id_remove(memcg);
>  	mem_cgroup_free(memcg);
>  	return ERR_PTR(-ENOMEM);
>  }

The only path which jumps to fail: here (in the current mmotm tree) is 
	error = memcg_online_kmem(memcg);
	if (error)
		goto fail;

AFAICS and the only failure path in memcg_online_kmem
	memcg_id = memcg_alloc_cache_id();
	if (memcg_id < 0)
		return memcg_id;

I am not entirely clear on memcg_alloc_cache_id but it seems we do clean
up properly. Or am I missing something?
-- 
Michal Hocko
SUSE Labs