From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751893AbYKLHdq (ORCPT ); Wed, 12 Nov 2008 02:33:46 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751077AbYKLHdh (ORCPT ); Wed, 12 Nov 2008 02:33:37 -0500 Received: from fgwmail7.fujitsu.co.jp ([192.51.44.37]:49487 "EHLO fgwmail7.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751022AbYKLHdg (ORCPT ); Wed, 12 Nov 2008 02:33:36 -0500 Date: Wed, 12 Nov 2008 16:32:56 +0900 From: KAMEZAWA Hiroyuki To: KAMEZAWA Hiroyuki Cc: "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , "balbir@linux.vnet.ibm.com" , "menage@google.com" , "nishimura@mxp.nes.nec.co.jp" , "lizf@cn.fujitsu.com" , "akpm@linux-foundation.org" Subject: [PATCH] [BUGFIX]cgroup: fix potential deadlock in pre_destroy (v2) Message-Id: <20081112163256.b36d6952.kamezawa.hiroyu@jp.fujitsu.com> In-Reply-To: <20081112133002.15c929c3.kamezawa.hiroyu@jp.fujitsu.com> References: <20081112133002.15c929c3.kamezawa.hiroyu@jp.fujitsu.com> Organization: FUJITSU Co. LTD. X-Mailer: Sylpheed 2.5.0 (GTK+ 2.10.14; i686-pc-mingw32) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is fixed one. Thank you for all help. Regards, -Kame == As Balbir pointed out, memcg's pre_destroy handler has potential deadlock. It has following lock sequence. cgroup_mutex (cgroup_rmdir) -> pre_destroy -> mem_cgroup_pre_destroy-> force_empty -> cpu_hotplug.lock. (lru_add_drain_all-> schedule_work-> get_online_cpus) But, cpuset has following. cpu_hotplug.lock (call notifier) -> cgroup_mutex. (within notifier) Then, this lock sequence should be fixed. Considering how pre_destroy works, it's not necessary to holding cgroup_mutex() while calling it. As side effect, we don't have to wait at this mutex while memcg's force_empty works.(it can be long when there are tons of pages.) Signed-off-by: KAMEZAWA Hiroyuki --- kernel/cgroup.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) Index: mmotm-2.6.28-Nov10/kernel/cgroup.c =================================================================== --- mmotm-2.6.28-Nov10.orig/kernel/cgroup.c +++ mmotm-2.6.28-Nov10/kernel/cgroup.c @@ -2475,10 +2475,7 @@ static int cgroup_rmdir(struct inode *un mutex_unlock(&cgroup_mutex); return -EBUSY; } - - parent = cgrp->parent; - root = cgrp->root; - sb = root->sb; + mutex_unlock(&cgroup_mutex); /* * Call pre_destroy handlers of subsys. Notify subsystems @@ -2486,7 +2483,14 @@ static int cgroup_rmdir(struct inode *un */ cgroup_call_pre_destroy(cgrp); - if (cgroup_has_css_refs(cgrp)) { + mutex_lock(&cgroup_mutex); + parent = cgrp->parent; + root = cgrp->root; + sb = root->sb; + + if (atomic_read(&cgrp->count) + || !list_empty(&cgrp->children) + || cgroup_has_css_refs(cgrp)) { mutex_unlock(&cgroup_mutex); return -EBUSY; }