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 X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0AA38C07E96 for ; Tue, 6 Jul 2021 14:40:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E1E2D6135C for ; Tue, 6 Jul 2021 14:40:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231545AbhGFOnb (ORCPT ); Tue, 6 Jul 2021 10:43:31 -0400 Received: from szxga01-in.huawei.com ([45.249.212.187]:6072 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232397AbhGFOna (ORCPT ); Tue, 6 Jul 2021 10:43:30 -0400 Received: from dggeme752-chm.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4GK4pb5WSFzXphc; Tue, 6 Jul 2021 22:35:19 +0800 (CST) Received: from [10.174.178.134] (10.174.178.134) by dggeme752-chm.china.huawei.com (10.3.19.98) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Tue, 6 Jul 2021 22:40:47 +0800 Subject: Re: [RFC PATCH 1/4] ext4: check and update i_disksize properly To: Jan Kara CC: , , , References: <20210706024210.746788-1-yi.zhang@huawei.com> <20210706024210.746788-2-yi.zhang@huawei.com> <20210706121123.GB7922@quack2.suse.cz> From: Zhang Yi Message-ID: <32946f62-631e-d752-9fcf-e89b568e2e7f@huawei.com> Date: Tue, 6 Jul 2021 22:40:46 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20210706121123.GB7922@quack2.suse.cz> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.134] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggeme752-chm.china.huawei.com (10.3.19.98) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On 2021/7/6 20:11, Jan Kara wrote: > On Tue 06-07-21 10:42:07, Zhang Yi wrote: >> After commit 3da40c7b0898 ("ext4: only call ext4_truncate when size <= >> isize"), i_disksize could always be updated to i_size in ext4_setattr(), >> and it seems that there is no other way that could appear >> i_disksize < i_size besides the delalloc write. In the case of delay > > Well, there are also direct IO writes which have temporarily i_disksize < > i_size but when you hold i_rwsem, you're right that delalloc is the only > reason why you can see i_disksize < i_size AFAIK. > >> alloc write, ext4_writepages() could update i_disksize for the new delay >> allocated blocks properly. So we could switch to check i_size instead >> of i_disksize in ext4_da_write_end() when write to the end of the file. > > I agree that since ext4_da_should_update_i_disksize() needs to return true > for us to touch i_disksize, writeback has to have already allocated block > underlying the end of write (new_i_size position) and thus we are > guaranteed that writeback will also soon update i_disksize after the > new_i_size position. So I agree that your switch to testing i_size instead > of i_disksize should not have any bad effect... Thinking about this some > more why do we need i_disksize update in ext4_da_write_end() at all? The > page will be dirtied and when writeback will happen we will update > i_disksize to i_size. Updating i_disksize earlier brings no benefit - the user > will see zeros instead of valid data if we crash before the writeback > happened. Am I missing something guys? > Hi, Jan. Do you remember the patch and question I asked 2 years ago[1][2]? The case of new_i_size > i_size && ext4_da_should_update_i_disksize() here means partial block append write, ext4_writepages() does not update i_disksize for this case now. And the journal data=ordered mode also cannot guarantee write data before metadata. So we cannot guarantee we cannot see zeros where data was written after crash. Thanks, Yi. [1]https://lore.kernel.org/linux-ext4/20190404101823.GA22313@quack2.suse.cz/ [2]https://lore.kernel.org/linux-ext4/20190405091258.GA1600@quack2.suse.cz/ > >> we also could remove ext4_mark_inode_dirty() together because >> generic_write_end() will dirty the inode. >> >> Signed-off-by: Zhang Yi >> --- >> fs/ext4/inode.c | 21 ++++++++------------- >> 1 file changed, 8 insertions(+), 13 deletions(-) >> >> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c >> index d8de607849df..6f6a61f3ae5f 100644 >> --- a/fs/ext4/inode.c >> +++ b/fs/ext4/inode.c >> @@ -3087,32 +3087,27 @@ static int ext4_da_write_end(struct file *file, >> * generic_write_end() will run mark_inode_dirty() if i_size >> * changes. So let's piggyback the i_disksize mark_inode_dirty >> * into that. >> + * >> + * Check i_size not i_disksize here because ext4_writepages() could >> + * update i_disksize from i_size for delay allocated blocks properly. >> */ >> new_i_size = pos + copied; >> - if (copied && new_i_size > EXT4_I(inode)->i_disksize) { >> + if (copied && new_i_size > inode->i_size) { >> if (ext4_has_inline_data(inode) || >> - ext4_da_should_update_i_disksize(page, end)) { >> + ext4_da_should_update_i_disksize(page, end)) >> ext4_update_i_disksize(inode, new_i_size); >> - /* We need to mark inode dirty even if >> - * new_i_size is less that inode->i_size >> - * bu greater than i_disksize.(hint delalloc) >> - */ >> - ret = ext4_mark_inode_dirty(handle, inode); >> - } >> } >> >> if (write_mode != CONVERT_INLINE_DATA && >> ext4_test_inode_state(inode, EXT4_STATE_MAY_INLINE_DATA) && >> ext4_has_inline_data(inode)) >> - ret2 = ext4_da_write_inline_data_end(inode, pos, len, copied, >> + ret = ext4_da_write_inline_data_end(inode, pos, len, copied, >> page); >> else >> - ret2 = generic_write_end(file, mapping, pos, len, copied, >> + ret = generic_write_end(file, mapping, pos, len, copied, >> page, fsdata); >> >> - copied = ret2; >> - if (ret2 < 0) >> - ret = ret2; >> + copied = ret; >> ret2 = ext4_journal_stop(handle); >> if (unlikely(ret2 && !ret)) >> ret = ret2; >> -- >> 2.31.1 >>