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 06592C77B73 for ; Thu, 27 Apr 2023 06:37:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242954AbjD0GhL (ORCPT ); Thu, 27 Apr 2023 02:37:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41534 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242907AbjD0GhK (ORCPT ); Thu, 27 Apr 2023 02:37:10 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 358204497; Wed, 26 Apr 2023 23:37:09 -0700 (PDT) Received: from dggpeml500021.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4Q6QwJ0kWnzsR8d; Thu, 27 Apr 2023 14:35:28 +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 14:37:06 +0800 Message-ID: Date: Thu, 27 Apr 2023 14:36:51 +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 To: Ming Lei , Matthew Wilcox CC: Theodore Ts'o , , Andreas Dilger , , Andrew Morton , , , Dave Chinner , Eric Sandeen , Christoph Hellwig , Zhang Yi , yangerkun , Baokun Li References: Content-Language: en-US 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: dggems706-chm.china.huawei.com (10.3.19.183) To dggpeml500021.china.huawei.com (7.185.36.21) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org 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. 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 ``` >> 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(). -- With Best Regards, Baokun Li .