From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754580AbbAVOfA (ORCPT ); Thu, 22 Jan 2015 09:35:00 -0500 Received: from mail-qa0-f51.google.com ([209.85.216.51]:60009 "EHLO mail-qa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751602AbbAVOe6 (ORCPT ); Thu, 22 Jan 2015 09:34:58 -0500 Date: Thu, 22 Jan 2015 09:34:54 -0500 From: Tejun Heo To: Johannes Weiner Cc: Will Deacon , "Suzuki K. Poulose" , Vladimir Davydov , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , "mhocko@suse.cz" , "akpm@linux-foundation.org" Subject: Re: [Regression] 3.19-rc3 : memcg: Hang in mount memcg Message-ID: <20150122143454.GA4507@htj.dyndns.org> References: <54B01335.4060901@arm.com> <20150110085525.GD2110@esperanza> <54BCFDCF.9090603@arm.com> <20150121163955.GM4549@arm.com> <20150122134550.GA13876@phnom.home.cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150122134550.GA13876@phnom.home.cmpxchg.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, Jan 22, 2015 at 08:45:50AM -0500, Johannes Weiner wrote: > diff --git a/kernel/cgroup.c b/kernel/cgroup.c > index bb263d0caab3..9a09308c8066 100644 > --- a/kernel/cgroup.c > +++ b/kernel/cgroup.c > @@ -1819,8 +1819,11 @@ static struct dentry *cgroup_mount(struct file_system_type *fs_type, > goto out_unlock; > } > > - if (root->flags ^ opts.flags) > - pr_warn("new mount options do not match the existing superblock, will be ignored\n"); > + if (root->flags ^ opts.flags) { > + pr_warn("new mount options do not match the existing superblock\n"); > + ret = -EBUSY; > + goto out_unlock; > + } Do we really need the above chunk? > @@ -1909,7 +1912,7 @@ static void cgroup_kill_sb(struct super_block *sb) > * > * And don't kill the default root. > */ > - if (css_has_online_children(&root->cgrp.self) || > + if (!list_empty(&root->cgrp.self.children) || > root == &cgrp_dfl_root) > cgroup_put(&root->cgrp); I tried to do something a bit more advanced so that eventual async release of dying children, if they happen, can also release the hierarchy but I don't think it really matters unless we can forcefully drain. So, shouldn't just the above part be enough? Thanks. -- tejun