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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3C615C43334 for ; Mon, 20 Jun 2022 09:05:02 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BEBAC8E0003; Mon, 20 Jun 2022 05:05:01 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B73BB6B007B; Mon, 20 Jun 2022 05:05:01 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A13D38E0003; Mon, 20 Jun 2022 05:05:01 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 8F67A6B0078 for ; Mon, 20 Jun 2022 05:05:01 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay12.hostedemail.com (Postfix) with ESMTP id 5DAA8120B3D for ; Mon, 20 Jun 2022 09:05:01 +0000 (UTC) X-FDA: 79598029602.17.076262E Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by imf15.hostedemail.com (Postfix) with ESMTP id B5D98A008F for ; Mon, 20 Jun 2022 09:04:59 +0000 (UTC) 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 ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655715900; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=dJxrApwnV16QZaxemV8f1p8X1AJlyrTjcFle8/k0Pi4=; b=myw+F3INkyBK+UrCH3DNAc8tJhRmVmuXjWoJO89wJ0C9wEt0Dg7BPu+sCIDzKUOa3/c9K3 YkEuEsnO4Bwei2n30vFKrtOUUw5XxGQV67hfKzHrTlIhyd/BRFqqamlsC4buEKu/b3pWYG lUNb7h1R6QNYo/y7FXcHiwJ5aK3GIBE= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655715900; a=rsa-sha256; cv=none; b=re6U3A9JbQUaFC261Zg/VqcGkOxNfqji8pzllV1bmkv6OG+3TYcg/obgSZ67Bd6bpJwqdS vdHPZJ6PxP7NCopkUoSn0wa+jsB31GJN9KH75pXWBtv7Jq05VL7l8SO5Y+rtn2XnafaaJc sgHe3UsUJyeLr3A0GVYiZB37St0JspI= ARC-Authentication-Results: i=1; imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.189 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Stat-Signature: 8xt6ma36w4j3y5ndh15z3sms7p1bzra5 Authentication-Results: imf15.hostedemail.com; dkim=none; spf=pass (imf15.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.189 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspamd-Queue-Id: B5D98A008F X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1655715899-318224 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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! > . >