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 7F38CC433F5 for ; Tue, 10 May 2022 12:46:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D58986B0072; Tue, 10 May 2022 08:46:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CE2E66B0073; Tue, 10 May 2022 08:46:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B5CB96B0074; Tue, 10 May 2022 08:46:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id A530A6B0072 for ; Tue, 10 May 2022 08:46:43 -0400 (EDT) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 775EC61851 for ; Tue, 10 May 2022 12:46:43 +0000 (UTC) X-FDA: 79449807486.02.417B6DF Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by imf20.hostedemail.com (Postfix) with ESMTP id 8E3B51C00A8 for ; Tue, 10 May 2022 12:46:33 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4KyHng1yzZz1JByM; Tue, 10 May 2022 20:45:27 +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; Tue, 10 May 2022 20:46:37 +0800 Subject: Re: [PATCH v3 1/3] mm/swapfile: unuse_pte can map random data if swap read fails To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= , "akpm@linux-foundation.org" , "willy@infradead.org" , "david@redhat.com" CC: "vbabka@suse.cz" , "dhowells@redhat.com" , "neilb@suse.de" , "apopple@nvidia.com" , "surenb@google.com" , "minchan@kernel.org" , "peterx@redhat.com" , "sfr@canb.auug.org.au" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" References: <20220424091105.48374-1-linmiaohe@huawei.com> <20220424091105.48374-2-linmiaohe@huawei.com> <20220510061712.GA162496@hori.linux.bs1.fc.nec.co.jp> From: Miaohe Lin Message-ID: <7b1ee28e-5ed2-6829-4573-035a39791cd7@huawei.com> Date: Tue, 10 May 2022 20:46:37 +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: <20220510061712.GA162496@hori.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected X-Rspamd-Queue-Id: 8E3B51C00A8 X-Stat-Signature: 8gui1py78mycm9w613y8mpiu6rkiooti X-Rspam-User: Authentication-Results: imf20.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf20.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.255 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Rspamd-Server: rspam09 X-HE-Tag: 1652186793-63540 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 2022/5/10 14:17, HORIGUCHI NAOYA(堀口 直也) wrote: > On Sun, Apr 24, 2022 at 05:11:03PM +0800, Miaohe Lin wrote: >> There is a bug in unuse_pte(): when swap page happens to be unreadable, >> page filled with random data is mapped into user address space. In case >> of error, a special swap entry indicating swap read fails is set to the >> page table. So the swapcache page can be freed and the user won't end up >> with a permanently mounted swap because a sector is bad. And if the page >> is accessed later, the user process will be killed so that corrupted data >> is never consumed. On the other hand, if the page is never accessed, the >> user won't even notice it. >> >> Signed-off-by: Miaohe Lin >> Acked-by: David Hildenbrand > > When I reproduced the issue (generated read error with dm-dust), I saw > infinite loop in the while loop in shmem_unuse_inode() (and this happens > even with this patch). I confirmed that shmem_swapin_page() returns -EIO, > but shmem_unuse_swap_entries() does not return the error to the callers, > so the while loop in shmem_unuse_inode() seems not break. In the current implementation, try_to_unuse will keep trying to do shmem_unuse unless -ENOMEM is returned from shmem_swapin_folio. This could be easily fixed by return -EIO when swapin error occurs. But the user will end up with a permanently mounted swap just because a sector was bad. One alternative is inventing a way to proceed the swapoff while preventing user from accessing the wrong data. But this might complicate the code a lot and I need to learn more about shmem. Any suggestion will be really grateful! Thanks! :) > > So maybe you need more code around shmem_unuse_inode() to handle the error? > > Thanks, > Naoya Horiguchi >