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 917F2C28D13 for ; Thu, 25 Aug 2022 09:52:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235036AbiHYJwm (ORCPT ); Thu, 25 Aug 2022 05:52:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55970 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241048AbiHYJug (ORCPT ); Thu, 25 Aug 2022 05:50:36 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 35EA9ACA10 for ; Thu, 25 Aug 2022 02:48:49 -0700 (PDT) Received: from dggpemm500021.china.huawei.com (unknown [172.30.72.54]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4MCykN4JL2z1N7Zs; Thu, 25 Aug 2022 17:45:16 +0800 (CST) Received: from dggpemm500001.china.huawei.com (7.185.36.107) by dggpemm500021.china.huawei.com (7.185.36.109) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 25 Aug 2022 17:48:47 +0800 Received: from [10.174.177.243] (10.174.177.243) by dggpemm500001.china.huawei.com (7.185.36.107) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 25 Aug 2022 17:48:47 +0800 Message-ID: Date: Thu, 25 Aug 2022 17:48:46 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Subject: Re: [PATCH 2/2] mm: slince possible data races about pgdat->kswapd Content-Language: en-US To: David Hildenbrand , Andrew Morton , CC: , References: <20220824071909.192535-1-wangkefeng.wang@huawei.com> <20220824071909.192535-2-wangkefeng.wang@huawei.com> <76d906e8-4c2b-0832-dc43-5fb49b5c6cc5@redhat.com> From: Kefeng Wang In-Reply-To: <76d906e8-4c2b-0832-dc43-5fb49b5c6cc5@redhat.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm500001.china.huawei.com (7.185.36.107) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/8/25 16:22, David Hildenbrand wrote: > On 25.08.22 04:34, Kefeng Wang wrote: >> On 2022/8/24 16:24, David Hildenbrand wrote: >>> On 24.08.22 09:19, Kefeng Wang wrote: >>>> The pgdat->kswapd could be accessed concurrently by kswapd_run() and >>>> kcompactd(), it don't be protected by any lock, which could leads to >>>> data races, adding READ/WRITE_ONCE() to slince it. >>> Okay, I think this patch here makes it clearer that we really just want >>> proper synchronization instead of hacking around it. >>> >>> What speaks against protecting pgdat->kswapd this using some proper >>> locking primitive? >> as comments about kswapd in struct pglist_data,  pgdat->kswapd should be >> >> protected by mem_hotplug_begin/done(), how about this way? >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 640fa76228dd..62018f35242a 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1983,7 +1983,13 @@ static inline bool is_via_compact_memory(int order) >> >>  static bool kswapd_is_running(pg_data_t *pgdat) >>  { >> -       return pgdat->kswapd && task_is_running(pgdat->kswapd); >> +       bool running; >> + >> +       mem_hotplug_begin(); >> +       running = pgdat->kswapd && task_is_running(pgdat->kswapd); >> +       mem_hotplug_end(); >> + >> +       return running; >>  } > I'd much rather just use a dedicated lock that does not involve memory > hotplug. The issue only occurred due memory hotplug, without mem-hotplug, the kswapd won't stop or re-run, there is no above issue too, add a new lock would be duplicated, but the scope of protection is smaller, I could repost with new lock if no more comment. > >