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 C27B5C6FD1D for ; Tue, 21 Mar 2023 01:29:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230228AbjCUB3t (ORCPT ); Mon, 20 Mar 2023 21:29:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36686 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230257AbjCUB3q (ORCPT ); Mon, 20 Mar 2023 21:29:46 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AC1D52068D; Mon, 20 Mar 2023 18:29:42 -0700 (PDT) Received: from kwepemm600013.china.huawei.com (unknown [172.30.72.55]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4PgYpz13V6znYSS; Tue, 21 Mar 2023 09:26:35 +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; Tue, 21 Mar 2023 09:29:39 +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> <48deeadf-05cd-3535-a589-907cfa252799@huawei.com> <20230320162446.vkqsxxcsmv4cacwa@quack3> From: Zhihao Cheng Message-ID: <60c01340-d7f5-ad20-4d5f-2c473de459cc@huawei.com> Date: Tue, 21 Mar 2023 09:29:39 +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: <20230320162446.vkqsxxcsmv4cacwa@quack3> Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.46] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To kwepemm600013.china.huawei.com (7.193.23.68) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org > On Mon 20-03-23 20:49:07, Zhihao Cheng wrote: >> [...] >> >>>> 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. > > Well, yeah, probably not trivial but still desirable ;). Will you look into > that? > > Honza > I'am happy to investigate it, maybe it will take some time, and I'm also glad to help review code if somebody come up a solution firstly.