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 A07A8C43334 for ; Mon, 20 Jun 2022 09:05:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240474AbiFTJFK (ORCPT ); Mon, 20 Jun 2022 05:05:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47470 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240455AbiFTJE4 (ORCPT ); Mon, 20 Jun 2022 05:04:56 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2F86BDEB for ; Mon, 20 Jun 2022 02:04:55 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4LRNxd3088zDsK6; Mon, 20 Jun 2022 17:04:21 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Mon, 20 Jun 2022 17:04:50 +0800 Subject: Re: [PATCH v2 2/3] mm/swapfile: fix possible data races of inuse_pages To: "Huang, Ying" CC: , , , References: <20220608144031.829-1-linmiaohe@huawei.com> <20220608144031.829-3-linmiaohe@huawei.com> <87edzjrcq8.fsf@yhuang6-desk2.ccr.corp.intel.com> From: Miaohe Lin Message-ID: <13414d6a-9e72-fb6c-f0a8-8b83ba0455de@huawei.com> Date: Mon, 20 Jun 2022 17:04:50 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <87edzjrcq8.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Type: text/plain; charset="windows-1252" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/6/20 15:54, Huang, Ying wrote: > Miaohe Lin writes: > >> si->inuse_pages could still be accessed concurrently now. The plain reads >> outside si->lock critical section, i.e. swap_show and si_swapinfo, which >> results in data races. But these should be ok because they're just used >> for showing swap info. >> >> Signed-off-by: Miaohe Lin >> Reviewed-by: David Hildenbrand >> --- >> mm/swapfile.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/mm/swapfile.c b/mm/swapfile.c >> index d2bead7b8b70..3fa26f6971e9 100644 >> --- a/mm/swapfile.c >> +++ b/mm/swapfile.c >> @@ -2646,7 +2646,7 @@ static int swap_show(struct seq_file *swap, void *v) >> } >> >> bytes = si->pages << (PAGE_SHIFT - 10); >> - inuse = si->inuse_pages << (PAGE_SHIFT - 10); >> + inuse = READ_ONCE(si->inuse_pages) << (PAGE_SHIFT - 10); >> >> file = si->swap_file; >> len = seq_file_path(swap, file, " \t\n\\"); >> @@ -3265,7 +3265,7 @@ void si_swapinfo(struct sysinfo *val) >> struct swap_info_struct *si = swap_info[type]; >> >> if ((si->flags & SWP_USED) && !(si->flags & SWP_WRITEOK)) >> - nr_to_be_unused += si->inuse_pages; >> + nr_to_be_unused += READ_ONCE(si->inuse_pages); >> } >> val->freeswap = atomic_long_read(&nr_swap_pages) + nr_to_be_unused; >> val->totalswap = total_swap_pages + nr_to_be_unused; > > READ_ONCE() should be paired with WRITE_ONCE(). So, change the writer > side too? READ_ONCE() is used to fix the complaint of concurrent accessing to si->inuse_pages from KCSAN here. The similar commit is 218209487c3d ("mm/swapfile: fix data races in try_to_unuse()"). IMHO, it's fine to see a not-uptodate value of si->inuse_pages because it's just used for showing swap info. So WRITE_ONCE() is not obligatory. Or am I miss something? > > Best Regards, > Huang, Ying Thanks! > . >