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 B5BACCCA479 for ; Mon, 20 Jun 2022 12:24:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 385AC6B0071; Mon, 20 Jun 2022 08:24:04 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 30E778E0001; Mon, 20 Jun 2022 08:24:04 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1B0496B0074; Mon, 20 Jun 2022 08:24:04 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 0BEA96B0071 for ; Mon, 20 Jun 2022 08:24:04 -0400 (EDT) Received: from smtpin27.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id D9A3820F41 for ; Mon, 20 Jun 2022 12:24:03 +0000 (UTC) X-FDA: 79598531166.27.0201498 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf16.hostedemail.com (Postfix) with ESMTP id 95244180023 for ; Mon, 20 Jun 2022 12:23:51 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LRTHj6XgkzSgtk; Mon, 20 Jun 2022 20:20:17 +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 20:23:33 +0800 Subject: Re: [PATCH v2 2/3] mm/swapfile: fix possible data races of inuse_pages To: Muchun Song , "Huang, Ying" , CC: , , , References: <20220608144031.829-1-linmiaohe@huawei.com> <20220608144031.829-3-linmiaohe@huawei.com> <87edzjrcq8.fsf@yhuang6-desk2.ccr.corp.intel.com> <13414d6a-9e72-fb6c-f0a8-8b83ba0455de@huawei.com> From: Miaohe Lin Message-ID: <09ffac27-7fe9-0977-cb33-30433e78e662@huawei.com> Date: Mon, 20 Jun 2022 20:23:33 +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: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) 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=1655727841; 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=i/JhoZcKsg2tka9qaxFlsD8UiCBq/4K0MyCpaXi11K0=; b=OYKKtFhlKNiT9a+gR+Z9ch1OJD1Hw6KP5BplW702GUuBgExbg3mFwQGQz3emo1EJxL0NuR 5lsxr6WtFAZWmPGUylPGLsbR+d7gjO/h4wm7BRDuGWQ5aJobWIQGHNihEF1XHwZLwh1gEU zyhdHCkF35irGKJRm9SAiYYitYqgQeI= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655727841; a=rsa-sha256; cv=none; b=yOkuLEZfYABUEYZW06jAB0k+ImRktLzxg6OrZicwIhbh2/jWMiyFoYAKmiyeL8WyM0xySk LbJ/9ePRnu4Ppfp/njWdqHOqeBxzy6Ldb3kOP/2KnUvWAkrkCGzJNCGWyO+sceNbl/n2L2 5qz9+AQLfu4Ha+fsWpzLxoSF+jZwmSE= ARC-Authentication-Results: i=1; imf16.hostedemail.com; dkim=none; spf=pass (imf16.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Stat-Signature: 9jh1f336kkp3u1cymgtmhzhfuf9wdodz Authentication-Results: imf16.hostedemail.com; dkim=none; spf=pass (imf16.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspamd-Queue-Id: 95244180023 X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1655727831-171343 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 17:23, Muchun Song wrote: > On Mon, Jun 20, 2022 at 05:04:50PM +0800, Miaohe Lin wrote: >> 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 > > I think the fix 218209487c3d is incomplete. The write side in swap_range_free() should > also be fixed. Otherwise, IIUC, it cannot stop KCSAN complaining. I tend to agree with you. READ_ONCE() should be paired with WRITE_ONCE() theoretically. But WRITTE_ONCE() is ignored while the commit is introduced. Add Qian Cai for helping verify it. It's very kind of @Qian Cai if he could tell us whether WRITTE_ONCE() is ignored deliberately. Thanks all of you. :) > >> 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! >> >>> . >>> >> >> > . >