From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f200.google.com (mail-wr0-f200.google.com [209.85.128.200]) by kanga.kvack.org (Postfix) with ESMTP id BF1A06B0005 for ; Fri, 13 Apr 2018 07:02:06 -0400 (EDT) Received: by mail-wr0-f200.google.com with SMTP id h1so4192533wre.0 for ; Fri, 13 Apr 2018 04:02:06 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id d28si2026019eda.68.2018.04.13.04.02.05 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 13 Apr 2018 04:02:05 -0700 (PDT) Date: Fri, 13 Apr 2018 13:02:00 +0200 From: Michal Hocko Subject: Re: [PATCH] memcg: Remove memcg_cgroup::id from IDR on mem_cgroup_css_alloc() failure Message-ID: <20180413110200.GG17484@dhcp22.suse.cz> References: <152354470916.22460.14397070748001974638.stgit@localhost.localdomain> <20180413085553.GF17484@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Kirill Tkhai 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 On Fri 13-04-18 12:35:22, Kirill Tkhai wrote: > On 13.04.2018 11:55, Michal Hocko wrote: > > 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? > > memcg_alloc_cache_id() may allocate a lot of memory, in case of the system reached > memcg_nr_cache_ids cgroups. In this case it iterates over all LRU lists, and double > size of every of them. In case of memory pressure it can fail. If this occurs, > mem_cgroup::id is not unhashed from IDR and we leak this id. OK, my bad I was looking at the bad code path. So you want to clean up after mem_cgroup_alloc not memcg_online_kmem. Now it makes much more sense. Sorry for the confusion on my end. Anyway, shouldn't we do the thing in mem_cgroup_free() to be symmetric to mem_cgroup_alloc? -- Michal Hocko SUSE Labs