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 8803DC77B61 for ; Thu, 27 Apr 2023 11:28:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243741AbjD0L2I (ORCPT ); Thu, 27 Apr 2023 07:28:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39856 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243416AbjD0L2H (ORCPT ); Thu, 27 Apr 2023 07:28:07 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CAC0F59EC for ; Thu, 27 Apr 2023 04:27:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1682594843; 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=GvY4p7P7cJsg0/C+DT6cOBtihMGDlSNrlTaMona+HC4=; b=NRxpLZJFUadTKBbcn9lYHlbABDRQi9ZPef0oHMQybtCTewrHegyoFqKg8CBqtlWKGipcyg CO00sXEsMwKYoTEP44ntB/STRdh0+czncL1l7ctMwRiq7RZX/3yNeR62oiecChjwnT68HG fMd1diWatqlhiAWEhkJSeLqBMru04mw= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-471-i-P2r6DfNfq2gp1vlaW-_Q-1; Thu, 27 Apr 2023 07:27:17 -0400 X-MC-Unique: i-P2r6DfNfq2gp1vlaW-_Q-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 169CA1C04190; Thu, 27 Apr 2023 11:27:17 +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 6303F1121315; Thu, 27 Apr 2023 11:27:08 +0000 (UTC) Date: Thu, 27 Apr 2023 19:27:04 +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: <663b10eb-4b61-c445-c07c-90c99f629c74@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <663b10eb-4b61-c445-c07c-90c99f629c74@huawei.com> 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 07:19:35PM +0800, Baokun Li wrote: > 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. OK, I will test it tomorrow. But I am afraid if it can avoid the issue completely because the old write task hang in balance_dirty_pages() may still write/dirty pages if it is one very big size write IO. Thanks, Ming