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 B6285C433EF for ; Fri, 21 Jan 2022 08:33:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1379601AbiAUIdE (ORCPT ); Fri, 21 Jan 2022 03:33:04 -0500 Received: from szxga02-in.huawei.com ([45.249.212.188]:30291 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231392AbiAUIdC (ORCPT ); Fri, 21 Jan 2022 03:33:02 -0500 Received: from dggpeml500023.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4JgCKp0TVXzbjyx; Fri, 21 Jan 2022 16:32:14 +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 15.1.2308.20; Fri, 21 Jan 2022 16:33:00 +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 15.1.2308.20; Fri, 21 Jan 2022 16:33:00 +0800 Message-ID: Date: Fri, 21 Jan 2022 16:33:00 +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: [Question] set_cpus_allowed_ptr() call failed at cpuset_attach() To: =?UTF-8?Q?Michal_Koutn=c3=bd?= CC: Tejun Heo , , , , References: <09ce5796-798e-83d0-f1a6-ba38a787bfc5@huawei.com> <4415cd09-6de3-bb2d-386d-8beb4927fb46@huawei.com> <20220119130221.GA31037@blackbody.suse.cz> <20220120140222.GA27269@blackbody.suse.cz> From: Zhang Qiao In-Reply-To: <20220120140222.GA27269@blackbody.suse.cz> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.111.186] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) 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 2022/1/20 22:02, Michal Koutný 写道: > On Thu, Jan 20, 2022 at 03:14:22PM +0800, Zhang Qiao wrote: >> i think the troublesome scenario as follows: >> cpuset_can_attach >> down_read(cpuset_rwsem) >> // check all migratees >> up_read(cpuset_rwsem) >> [ _cpu_down / cpuhp_setup_state ] >> cpuset_attach >> down_write(cpuset_rwsem) >> guarantee_online_cpus() // (load cpus_attach) >> sched_cpu_deactivate >> set_cpu_active(cpu, false) // 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) >> schedule_work >> ... >> cpuset_hotplug_update_tasks >> down_write(cpuset_rwsem) >> up_write(cpuset_rwsem) >> ... flush_work >> [ _cpu_down / cpu_up_down_serialize_trainwrecks ] > > Thanks, a locking loophole indeed. > > FTR, meanwhile I noticed: a) cpuset_fork() looks buggy when > CLONE_INTO_CGROUP (and dst.cpus != src.cpus), b) it'd be affected with > similar hotplug race. Yes, it shouldn't set the current task's cpumak to the child process at cpuset_fork(). Regards, Qiao . > > Michal > . >