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 C3428C7618A for ; Mon, 20 Mar 2023 12:51:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231548AbjCTMvV (ORCPT ); Mon, 20 Mar 2023 08:51:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55040 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231520AbjCTMu5 (ORCPT ); Mon, 20 Mar 2023 08:50:57 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 196E116ACA; Mon, 20 Mar 2023 05:49:34 -0700 (PDT) Received: from kwepemm600013.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4PgF0c5jkgz9vFC; Mon, 20 Mar 2023 20:48:48 +0800 (CST) Received: from [10.174.178.46] (10.174.178.46) by kwepemm600013.china.huawei.com (7.193.23.68) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.21; Mon, 20 Mar 2023 20:49:08 +0800 Subject: Re: [PATCH] ext4: Fix i_disksize exceeding i_size problem in paritally written case To: Jan Kara CC: , , , , , , References: <20230317013553.1009553-1-chengzhihao1@huawei.com> <20230317124513.drx3wywcjnap5jme@quack3> <884950ac-e60a-d331-9f68-310ab81ee595@huawei.com> <71990726-c677-34df-d29b-a0fec1a6f68c@huawei.com> <20230320112038.3q2eqpv6xsmj22br@quack3> From: Zhihao Cheng Message-ID: <48deeadf-05cd-3535-a589-907cfa252799@huawei.com> Date: Mon, 20 Mar 2023 20:49:07 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: <20230320112038.3q2eqpv6xsmj22br@quack3> Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.46] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To kwepemm600013.china.huawei.com (7.193.23.68) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [...] >> BTW, I want send another patch as follows: >> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c >> index bf0b7dea4900..570a687ae847 100644 >> --- a/fs/ext4/inode.c >> +++ b/fs/ext4/inode.c >> @@ -3149,7 +3149,7 @@ static int ext4_da_write_end(struct file *file, >> return ext4_write_inline_data_end(inode, pos, len, copied, >> page); >> >> start = pos & (PAGE_SIZE - 1); >> - end = start + copied - 1; >> + end = start + (copied ? copied - 1 : copied); >> >> /* >> * Since we are holding inode lock, we are sure i_disksize <= >> @@ -3167,7 +3167,7 @@ static int ext4_da_write_end(struct file *file, >> * ext4_da_write_inline_data_end(). >> */ >> new_i_size = pos + copied; >> - if (copied && new_i_size > inode->i_size && >> + if (new_i_size > inode->i_size && >> ext4_da_should_update_i_disksize(page, end)) >> ext4_update_i_disksize(inode, new_i_size); >> >> This modification handle unconsistent i_size and i_disksize imported by >> ea51d132dbf9 ("ext4: avoid hangs in ext4_da_should_update_i_disksize()"). >> >> Paritially written may display a fake inode size for user, for example: >> >> >> >> i_disksize=1 >> >> generic_perform_write >> >> copied = iov_iter_copy_from_user_atomic(len) // copied = 0 >> >> ext4_da_write_end // skip updating i_disksize >> >> generic_write_end >> >> if (pos + copied > inode->i_size) { // 10 + 0 > 1, true >> >> i_size_write(inode, pos + copied); // i_size = 10 >> >> } >> >> >> >> 0 1 10 4096 >> >> |_|_______|_________..._____| >> >> | | >> >> i_size pos >> >> >> >> Now, user see the i_size is 10 (i_disksize is still 1). After inode >> >> destroyed, user will get the i_size is 1 read from disk. > > OK, but shouldn't we rather change generic_write_end() to not increase > i_size if no write happened? Because that is what seems somewhat > problematic... > > Honza > After looking through some code, I find some other places have similar problem: 1. In ext4_write_end(), i_size is updated by ext4 not generic_write_end(). 2. The iommap framework, i_size is updated even copied is zero. 3. ubifs_write_end, i_size is updated even copied is zero. It seems that fixing all places is not an easy work.