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 1C331C00140 for ; Wed, 24 Aug 2022 09:53:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236275AbiHXJxd (ORCPT ); Wed, 24 Aug 2022 05:53:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230492AbiHXJxO (ORCPT ); Wed, 24 Aug 2022 05:53:14 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12DF29751B for ; Wed, 24 Aug 2022 02:52:01 -0700 (PDT) Received: from dggpemm500023.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4MCLrh3Gv8zlWPp; Wed, 24 Aug 2022 17:48:36 +0800 (CST) Received: from dggpemm500001.china.huawei.com (7.185.36.107) by dggpemm500023.china.huawei.com (7.185.36.83) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Wed, 24 Aug 2022 17:51:50 +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; Wed, 24 Aug 2022 17:51:50 +0800 Message-ID: Date: Wed, 24 Aug 2022 17:51:49 +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> From: Kefeng Wang In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) 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 2022/8/24 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? So add a new lock into struct pglist_data to protect pgdat->kswapd，other option, thanks. >> Signed-off-by: Kefeng Wang >> --- >> mm/compaction.c | 4 +++- >> mm/vmscan.c | 8 ++++---- >> 2 files changed, 7 insertions(+), 5 deletions(-) >> >> diff --git a/mm/compaction.c b/mm/compaction.c >> index 640fa76228dd..aa1cfe47f046 100644 >> --- a/mm/compaction.c >> +++ b/mm/compaction.c >> @@ -1983,7 +1983,9 @@ 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); >> + struct task_struct *t = READ_ONCE(pgdat->kswapd); >> + >> + return t && task_is_running(t); >> } >> >> /* >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index 08c6497f76c3..65b19ca8c8ee 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -4644,7 +4644,7 @@ void kswapd_run(int nid) >> pg_data_t *pgdat = NODE_DATA(nid); >> struct task_struct *t; >> >> - if (pgdat->kswapd) >> + if (READ_ONCE(pgdat->kswapd)) >> return; >> >> t = kthread_run(kswapd, pgdat, "kswapd%d", nid); >> @@ -4653,7 +4653,7 @@ void kswapd_run(int nid) >> BUG_ON(system_state < SYSTEM_RUNNING); >> pr_err("Failed to start kswapd on node %d\n", nid); >> } else { >> - pgdat->kswapd = t; >> + WRITE_ONCE(pgdat->kswapd, t); >> } >> } >> >> @@ -4663,11 +4663,11 @@ void kswapd_run(int nid) >> */ >> void kswapd_stop(int nid) >> { >> - struct task_struct *kswapd = NODE_DATA(nid)->kswapd; >> + struct task_struct *kswapd = READ_ONCE(NODE_DATA(nid)->kswapd); >> >> if (kswapd) { >> kthread_stop(kswapd); >> - NODE_DATA(nid)->kswapd = NULL; >> + WRITE_ONCE(NODE_DATA(nid)->kswapd, NULL); >> } >> } >> >