From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 54323C433EF for ; Mon, 14 Mar 2022 09:12:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237838AbiCNJNS (ORCPT ); Mon, 14 Mar 2022 05:13:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40646 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237975AbiCNJNE (ORCPT ); Mon, 14 Mar 2022 05:13:04 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 22914433B5; Mon, 14 Mar 2022 02:11:54 -0700 (PDT) Received: from dggpeml500023.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KH9dq1k19zcb1j; Mon, 14 Mar 2022 17:06:55 +0800 (CST) Received: from dggpeml500018.china.huawei.com (7.185.36.186) by dggpeml500023.china.huawei.com (7.185.36.114) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Mon, 14 Mar 2022 17:11:50 +0800 Received: from [10.67.111.186] (10.67.111.186) by dggpeml500018.china.huawei.com (7.185.36.186) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Mon, 14 Mar 2022 17:11:50 +0800 Message-ID: Date: Mon, 14 Mar 2022 17:11:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.1.1 Subject: Re: [PATCH 4.19 01/34] cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug To: Greg Kroah-Hartman , =?UTF-8?Q?Michal_Koutn=c3=bd?= CC: , , Zhao Gongyi , Waiman Long , Tejun Heo , Juri Lelli References: <20220228172207.090703467@linuxfoundation.org> <20220228172208.566431934@linuxfoundation.org> <20220308151232.GA21752@blackbody.suse.cz> From: Zhang Qiao In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.111.186] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpeml500018.china.huawei.com (7.185.36.186) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2022/3/14 16:06, Greg Kroah-Hartman 写道: > On Tue, Mar 08, 2022 at 04:12:32PM +0100, Michal Koutný wrote: >> Hello. >> >> On Mon, Feb 28, 2022 at 06:24:07PM +0100, Greg Kroah-Hartman wrote: >>> [...] >>> cpuset_attach() cpu hotplug >>> --------------------------- ---------------------- >>> down_write(cpuset_rwsem) >>> guarantee_online_cpus() // (load cpus_attach) >>> sched_cpu_deactivate >>> set_cpu_active() >>> // will change cpu_active_mask >>> set_cpus_allowed_ptr(cpus_attach) >>> __set_cpus_allowed_ptr_locked() >>> // (if the intersection of cpus_attach and >>> cpu_active_mask is empty, will return -EINVAL) >>> up_write(cpuset_rwsem) >>> [...] >>> --- a/kernel/cgroup/cpuset.c >>> +++ b/kernel/cgroup/cpuset.c >>> @@ -1528,6 +1528,7 @@ static void cpuset_attach(struct cgroup_ >>> cgroup_taskset_first(tset, &css); >>> cs = css_cs(css); >>> >>> + cpus_read_lock(); >>> mutex_lock(&cpuset_mutex); >> >> This backport (and possible older kernels) looks suspicious since it comes >> before commit d74b27d63a8b ("cgroup/cpuset: Change cpuset_rwsem and >> hotplug lock order") v5.4-rc1~176^2~30 when the locking order was: >> cpuset lock, cpus lock. >> >> At the same time it also comes before commit 710da3c8ea7d ("sched/core: >> Prevent race condition between cpuset and __sched_setscheduler()") >> v5.4-rc1~176^2~27 when neither __sched_setscheduler() cared and this >> race is similar. (The swapped locking may still conflict with >> rebuild_sched_domains() before d74b27d63a8b.) > > Thanks for noticing this. What do you recommend to do to resolve this? > > thanks, > hi, Please review the following patch to fix it. thanks. patch: [PATCH] cpuset: Fix unsafe lock order between cpuset lock and cpus lock The backport commit 4eec5fe1c680a ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug") looks suspicious since it comes before commit d74b27d63a8b ("cgroup/cpuset: Change cpuset_rwsem and hotplug lock order") v5.4-rc1~176^2~30 when the locking order was: cpuset lock, cpus lock. Fix it with the correct locking order and reduce the cpus locking range because only set_cpus_allowed_ptr() needs the protection of cpus lock. Fixes: 4eec5fe1c680a ("cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug") Reported-by: Michal Koutný Signed-off-by: Zhang Qiao --- kernel/cgroup/cpuset.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index d43d25acc..4e1c4232e 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1528,9 +1528,13 @@ static void cpuset_attach(struct cgroup_taskset *tset) cgroup_taskset_first(tset, &css); cs = css_cs(css); - cpus_read_lock(); mutex_lock(&cpuset_mutex); + /* + * It should hold cpus lock because a cpu offline event can + * cause set_cpus_allowed_ptr() failed. + */ + cpus_read_lock(); /* prepare for attach */ if (cs == &top_cpuset) cpumask_copy(cpus_attach, cpu_possible_mask); @@ -1549,6 +1553,7 @@ static void cpuset_attach(struct cgroup_taskset *tset) cpuset_change_task_nodemask(task, &cpuset_attach_nodemask_to); cpuset_update_task_spread_flag(cs, task); } + cpus_read_unlock(); /* * Change mm for all threadgroup leaders. This is expensive and may @@ -1584,7 +1589,6 @@ static void cpuset_attach(struct cgroup_taskset *tset) wake_up(&cpuset_attach_wq); mutex_unlock(&cpuset_mutex); - cpus_read_unlock(); } /* The various types of files and directories in a cpuset file system */ -- 2.18.0 > greg k-h > . >