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 DC5D7C77B73 for ; Thu, 27 Apr 2023 10:02:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243406AbjD0KCl (ORCPT ); Thu, 27 Apr 2023 06:02:41 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45430 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243405AbjD0KCi (ORCPT ); Thu, 27 Apr 2023 06:02:38 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E021244A9 for ; Thu, 27 Apr 2023 03:01:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1682589709; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cWUBtLVRFF9DJeWOTiQZdIEEXbV5A04d5aYZUT6wczQ=; b=Dfqaz1P1wMzZ1Ud2N6tMCLSvsJuLOkTIXOeCFPWva8rmzceZqs9mJJecfi2eeSuiqfYm9y +DykdApA083TDThnusnBPcLmbIwPwc8+Na3zuMatSdL+PZFN8eOHWWmRZMgEVpYAGgBBpn GOePHWhabokTocrrstjYlXHNSxix6dY= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-258-yvdQFQxbPu2rUTEKvJHsPw-1; Thu, 27 Apr 2023 06:01:44 -0400 X-MC-Unique: yvdQFQxbPu2rUTEKvJHsPw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 36CAC886462; Thu, 27 Apr 2023 10:01:43 +0000 (UTC) Received: from ovpn-8-26.pek2.redhat.com (ovpn-8-26.pek2.redhat.com [10.72.8.26]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5A62B1121314; Thu, 27 Apr 2023 10:01:33 +0000 (UTC) Date: Thu, 27 Apr 2023 18:01:28 +0800 From: Ming Lei To: Baokun Li Cc: Matthew Wilcox , Theodore Ts'o , linux-ext4@vger.kernel.org, Andreas Dilger , linux-block@vger.kernel.org, Andrew Morton , linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, Dave Chinner , Eric Sandeen , Christoph Hellwig , Zhang Yi , yangerkun , ming.lei@redhat.com Subject: Re: [ext4 io hang] buffered write io hang in balance_dirty_pages Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org 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