From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760957Ab3DBOQt (ORCPT ); Tue, 2 Apr 2013 10:16:49 -0400 Received: from cantor2.suse.de ([195.135.220.15]:46279 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756127Ab3DBOQs (ORCPT ); Tue, 2 Apr 2013 10:16:48 -0400 Date: Tue, 2 Apr 2013 16:16:46 +0200 From: Michal Hocko To: Li Zefan Cc: Glauber Costa , Johannes Weiner , KAMEZAWA Hiroyuki , LKML , Cgroups , linux-mm@kvack.org Subject: Re: [PATCH] memcg: don't do cleanup manually if mem_cgroup_css_online() fails Message-ID: <20130402141646.GQ24345@dhcp22.suse.cz> References: <515A8A40.6020406@huawei.com> <20130402121600.GK24345@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130402121600.GK24345@dhcp22.suse.cz> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 02-04-13 14:16:00, Michal Hocko wrote: > On Tue 02-04-13 15:35:28, Li Zefan wrote: > [...] > > @@ -6247,16 +6247,7 @@ mem_cgroup_css_online(struct cgroup *cont) > > > > error = memcg_init_kmem(memcg, &mem_cgroup_subsys); > > mutex_unlock(&memcg_create_mutex); > > - if (error) { > > - /* > > - * We call put now because our (and parent's) refcnts > > - * are already in place. mem_cgroup_put() will internally > > - * call __mem_cgroup_free, so return directly > > - */ > > - mem_cgroup_put(memcg); > > - if (parent->use_hierarchy) > > - mem_cgroup_put(parent); > > - } > > + > > return error; > > } > > The mem_cgroup_put(parent) part is incorrect because mem_cgroup_put goes > up the hierarchy already but I do not think mem_cgroup_put(memcg) should > go away as well. Who is going to free the last reference then? > > Maybe I am missing something but we have: OK, I was missing something but "there is one reference without put" still holds... cgroup_create css = ss->css_alloc(cgrp) mem_cgroup_css_alloc atomic_set(&memcg->refcnt, 1) online_css(ss, cgrp) mem_cgroup_css_online memcg_init_kmem mem_cgroup_get # refcnt = 2 memcg_update_all_caches memcg_update_cache_size # fails with ENOMEM goto err_destroy err_destroy: cgroup_destroy_locked(cgrp) offline_css mem_cgroup_css_offline There is one mem_cgroup_put from mem_cgroup_css_free from cgroup_diput but besides that I do not see any put after the patch is applied. So I think you really need to drop only the mem_cgroup_put on parent part. -- Michal Hocko SUSE Labs