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 DECFBC77B73 for ; Thu, 27 Apr 2023 07:33:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243008AbjD0Hdv (ORCPT ); Thu, 27 Apr 2023 03:33:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48670 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242667AbjD0Hdu (ORCPT ); Thu, 27 Apr 2023 03:33:50 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6F15419AC; Thu, 27 Apr 2023 00:33:47 -0700 (PDT) Received: from dggpeml500021.china.huawei.com (unknown [172.30.72.57]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Q6S6X2QkmzStFk; Thu, 27 Apr 2023 15:29:24 +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 15:33:42 +0800 Message-ID: <321a58db-da64-fea4-64b2-1dd6ae5e4976@huawei.com> Date: Thu, 27 Apr 2023 15:33:41 +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 , Matthew Wilcox CC: 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: dggems702-chm.china.huawei.com (10.3.19.179) 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 14:36, 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. > > 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(). > > On second thought, we can determine if the file system has become read-only when the ext4_file_write_iter() is called on a write file, even though the fs was not read-only when the file was opened. This would end the write process early and free up resources like xfs does. The patch is below, does anyone have any other thoughts? diff --git a/fs/ext4/file.c b/fs/ext4/file.c index d101b3b0c7da..d2966268ee41 100644 --- a/fs/ext4/file.c +++ b/fs/ext4/file.c @@ -699,6 +699,8 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)         if (unlikely(ext4_forced_shutdown(EXT4_SB(inode->i_sb))))                 return -EIO; +       if (unlikely(sb_rdonly(inode->i_sb))) +               return -EROFS;  #ifdef CONFIG_FS_DAX         if (IS_DAX(inode)) -- With Best Regards, Baokun Li .