From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752453Ab3AXGoF (ORCPT ); Thu, 24 Jan 2013 01:44:05 -0500 Received: from szxga01-in.huawei.com ([119.145.14.64]:60805 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751278Ab3AXGnz (ORCPT ); Thu, 24 Jan 2013 01:43:55 -0500 Message-ID: <5100D810.5020406@huawei.com> Date: Thu, 24 Jan 2013 14:43:28 +0800 From: Li Zefan User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130107 Thunderbird/17.0.2 MIME-Version: 1.0 To: Tejun Heo CC: cgroups , LKML Subject: [PATCH 1/2] cgroup: fix exit() vsrmdir() race Content-Type: text/plain; charset="GB2312" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.135.68.215] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In cgroup_exit() put_css_set_taskexit() is called without any lock, which might lead to accessing a freed cgroup: thread1 thread2 --------------------------------------------- exit() cgroup_exit() put_css_set_taskexit() atomic_dec(cgrp->count); rmdir(); /* not safe !! */ check_for_release(cgrp); rcu_read_lock() can be used to make sure the cgroup is alive. Signed-off-by: Li Zefan --- kernel/cgroup.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 368cff1..09c5869 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -422,12 +422,20 @@ static void __put_css_set(struct css_set *cg, int taskexit) struct cgroup *cgrp = link->cgrp; list_del(&link->cg_link_list); list_del(&link->cgrp_link_list); + + /* + * We may not be holding cgroup_mutex, and if cgrp->count is + * dropped to 0 the cgroup can be destroyed at any time, hence + * rcu_read_lock is used to keep it alive. + */ + rcu_read_lock(); if (atomic_dec_and_test(&cgrp->count) && notify_on_release(cgrp)) { if (taskexit) set_bit(CGRP_RELEASABLE, &cgrp->flags); check_for_release(cgrp); } + rcu_read_unlock(); kfree(link); } -- 1.8.0.2