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 5D3BBC61DA4 for ; Sat, 18 Mar 2023 08:51:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229892AbjCRIvM (ORCPT ); Sat, 18 Mar 2023 04:51:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54984 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229813AbjCRIvK (ORCPT ); Sat, 18 Mar 2023 04:51:10 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D255C38E9B; Sat, 18 Mar 2023 01:51:04 -0700 (PDT) Received: from kwepemm600013.china.huawei.com (unknown [172.30.72.53]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4Pdvlh3mSYznWtk; Sat, 18 Mar 2023 16:48:00 +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; Sat, 18 Mar 2023 16:51:01 +0800 Subject: Re: [PATCH] ext4: Fix i_disksize exceeding i_size problem in paritally written case From: Zhihao Cheng To: Jan Kara CC: , , , , , , References: <20230317013553.1009553-1-chengzhihao1@huawei.com> <20230317124513.drx3wywcjnap5jme@quack3> <884950ac-e60a-d331-9f68-310ab81ee595@huawei.com> Message-ID: <71990726-c677-34df-d29b-a0fec1a6f68c@huawei.com> Date: Sat, 18 Mar 2023 16:51:00 +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: <884950ac-e60a-d331-9f68-310ab81ee595@huawei.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.178.46] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) 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 > Hi, Jan >> On Fri 17-03-23 09:35:53, Zhihao Cheng wrote: >>> Following process makes i_disksize exceed i_size: >>> >>> generic_perform_write >>>   copied = iov_iter_copy_from_user_atomic(len) // copied < len >>>   ext4_da_write_end >>>   | ext4_update_i_disksize >>>   |  new_i_size = pos + copied; >>>   |  WRITE_ONCE(EXT4_I(inode)->i_disksize, newsize) // update i_disksize >>>   | generic_write_end >>>   |  copied = block_write_end(copied, len) // copied = 0 >>>   |   if (unlikely(copied < len)) >>>   |    if (!PageUptodate(page)) >>>   |     copied = 0; >>>   |  if (pos + copied > inode->i_size) // return false >>>   if (unlikely(copied == 0)) >>>    goto again; >>>   if (unlikely(iov_iter_fault_in_readable(i, bytes))) { >>>    status = -EFAULT; >>>    break; >>>   } >>> >>> We get i_disksize greater than i_size here, which could trigger WARNING >>> check 'i_size_read(inode) < EXT4_I(inode)->i_disksize' while doing dio: >>> >>> ext4_dio_write_iter >>>   iomap_dio_rw >>>    __iomap_dio_rw // return err, length is not aligned to 512 >>>   ext4_handle_inode_extension >>>    WARN_ON_ONCE(i_size_read(inode) < EXT4_I(inode)->i_disksize) // Oops >>> >>>   WARNING: CPU: 2 PID: 2609 at fs/ext4/file.c:319 >>>   CPU: 2 PID: 2609 Comm: aa Not tainted 6.3.0-rc2 >>>   RIP: 0010:ext4_file_write_iter+0xbc7 >>>   Call Trace: >>>    vfs_write+0x3b1 >>>    ksys_write+0x77 >>>    do_syscall_64+0x39 >>> >>> Fix it by putting block_write_end() before i_disksize updating just >>> like ext4_write_end() does. >>> >>> Fetch a reproducer in [Link]. >>> >>> Link: https://bugzilla.kernel.org/show_bug.cgi?id=217209 >>> Fixes: 64769240bd07f ("ext4: Add delayed allocation support in >>> data=writeback mode") >>> Signed-off-by: Zhihao Cheng >> >> Good catch (although practically this will hardly have any negative >> effect). But rather than opencoding generic_write_end() I'd do: >> >>          if (unlikely(copied < len) && !PageUptodate(page)) >>                  copied = 0; >> >> at the beginning of ext4_da_write_end() and that should solve these >> problems as well? >> > > Yes, your suggestion looks good, and I think we can put the checking > just after ext4_write_inline_data_end(Line 3150)? On the one hand, we > can pass original 'copied' value in trace_ext4_da_write_end(), one the > other hand, ext4_write_inline_data_end() already has this checking. > . 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.