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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76AF8C77B61 for ; Thu, 27 Apr 2023 11:19:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243695AbjD0LTw (ORCPT ); Thu, 27 Apr 2023 07:19:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59804 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243459AbjD0LTr (ORCPT ); Thu, 27 Apr 2023 07:19:47 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8A31C4C0B; Thu, 27 Apr 2023 04:19:41 -0700 (PDT) Received: from dggpeml500021.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Q6Y8z5xJ0zLnnY; Thu, 27 Apr 2023 19:16:51 +0800 (CST) Received: from [10.174.177.174] (10.174.177.174) by dggpeml500021.china.huawei.com (7.185.36.21) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Thu, 27 Apr 2023 19:19:35 +0800 Message-ID: <663b10eb-4b61-c445-c07c-90c99f629c74@huawei.com> Date: Thu, 27 Apr 2023 19:19:35 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.1.2 Subject: Re: [ext4 io hang] buffered write io hang in balance_dirty_pages Content-Language: en-US To: Ming Lei CC: Matthew Wilcox , Theodore Ts'o , , Andreas Dilger , , Andrew Morton , , , Dave Chinner , Eric Sandeen , Christoph Hellwig , Zhang Yi , yangerkun , Baokun Li References: From: Baokun Li In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.174] X-ClientProxiedBy: dggems704-chm.china.huawei.com (10.3.19.181) To dggpeml500021.china.huawei.com (7.185.36.21) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2023/4/27 18:01, Ming Lei wrote: > On Thu, Apr 27, 2023 at 02:36:51PM +0800, Baokun Li wrote: >> On 2023/4/27 12:50, Ming Lei wrote: >>> Hello Matthew, >>> >>> On Thu, Apr 27, 2023 at 04:58:36AM +0100, Matthew Wilcox wrote: >>>> On Thu, Apr 27, 2023 at 10:20:28AM +0800, Ming Lei wrote: >>>>> Hello Guys, >>>>> >>>>> I got one report in which buffered write IO hangs in balance_dirty_pages, >>>>> after one nvme block device is unplugged physically, then umount can't >>>>> succeed. >>>> That's a feature, not a bug ... the dd should continue indefinitely? >>> Can you explain what the feature is? And not see such 'issue' or 'feature' >>> on xfs. >>> >>> The device has been gone, so IMO it is reasonable to see FS buffered write IO >>> failed. Actually dmesg has shown that 'EXT4-fs (nvme0n1): Remounting >>> filesystem read-only'. Seems these things may confuse user. >> >> The reason for this difference is that ext4 and xfs handle errors >> differently. >> >> ext4 remounts the filesystem as read-only or even just continues, vfs_write >> does not check for these. > vfs_write may not find anything wrong, but ext4 remount could see that > disk is gone, which might happen during or after remount, however. > >> xfs shuts down the filesystem, so it returns a failure at >> xfs_file_write_iter when it finds an error. >> >> >> ``` ext4 >> ksys_write >>  vfs_write >>   ext4_file_write_iter >>    ext4_buffered_write_iter >>     ext4_write_checks >>      file_modified >>       file_modified_flags >>        __file_update_time >>         inode_update_time >>          generic_update_time >>           __mark_inode_dirty >>            ext4_dirty_inode ---> 2. void func, No propagating errors out >>             __ext4_journal_start_sb >>              ext4_journal_check_start ---> 1. Error found, remount-ro >>     generic_perform_write ---> 3. No error sensed, continue >>      balance_dirty_pages_ratelimited >>       balance_dirty_pages_ratelimited_flags >>        balance_dirty_pages >>         // 4. Sleeping waiting for dirty pages to be freed >>         __set_current_state(TASK_KILLABLE) >>         io_schedule_timeout(pause); >> ``` >> >> ``` xfs >> ksys_write >>  vfs_write >>   xfs_file_write_iter >>    if (xfs_is_shutdown(ip->i_mount)) >>      return -EIO;    ---> dd fail >> ``` > Thanks for the info which is really helpful for me to understand the > problem. > >>>> balance_dirty_pages() is sleeping in KILLABLE state, so kill -9 of >>>> the dd process should succeed. >>> Yeah, dd can be killed, however it may be any application(s), :-) >>> >>> Fortunately it won't cause trouble during reboot/power off, given >>> userspace will be killed at that time. >>> >>> >>> >>> Thanks, >>> Ming >>> >> Don't worry about that, we always set the current thread to TASK_KILLABLE >> >> while waiting in balance_dirty_pages(). > I have another concern, if 'dd' isn't killed, dirty pages won't be cleaned, and > these (big amount)memory becomes not usable, and typical scenario could be USB HDD > unplugged. > > > thanks, > Ming Yes, it is unreasonable to continue writing data with the previously opened fd after the file system becomes read-only, resulting in dirty page accumulation. I provided a patch in another reply. Could you help test if it can solve your problem? If it can indeed solve your problem, I will officially send it to the email list. -- With Best Regards, Baokun Li .