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 X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 85457C07E95 for ; Wed, 7 Jul 2021 23:52:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6210461CCF for ; Wed, 7 Jul 2021 23:52:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230015AbhGGXz0 (ORCPT ); Wed, 7 Jul 2021 19:55:26 -0400 Received: from outgoing-auth-1.mit.edu ([18.9.28.11]:55056 "EHLO outgoing.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S229519AbhGGXz0 (ORCPT ); Wed, 7 Jul 2021 19:55:26 -0400 Received: from cwcc.thunk.org (pool-72-74-133-215.bstnma.fios.verizon.net [72.74.133.215]) (authenticated bits=0) (User authenticated as tytso@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id 167NqfuW015376 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 7 Jul 2021 19:52:41 -0400 Received: by cwcc.thunk.org (Postfix, from userid 15806) id 2ED0115C3CC6; Wed, 7 Jul 2021 19:52:41 -0400 (EDT) Date: Wed, 7 Jul 2021 19:52:41 -0400 From: "Theodore Ts'o" To: Ivan Zahariev Cc: linux-ext4@vger.kernel.org Subject: Re: jbd2: fix deadlock while checkpoint thread waits commit thread to finish (backport to 4.14) Message-ID: References: <3221ced0-e8f3-53da-3474-28367272f35d@famzah.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3221ced0-e8f3-53da-3474-28367272f35d@famzah.net> Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Wed, Jul 07, 2021 at 09:42:25PM +0300, Ivan Zahariev wrote: > Hello, > > We're running Linux kernel 4.14.x and our systems occasionally suffer a bug > which is already fixed: https://github.com/torvalds/linux/commit/53cf978457325d8fb2cdecd7981b31a8229e446e > > This bugfix hasn't been ported to Linux kernels 4.14 or 4.19. The patch > applies cleanly. The two files "fs/jbd2/checkpoint.c" and > "fs/jbd2/journal.c" seem pretty identical in the affected sections compared > to kernel 5.4 where we have this bugfix already applied. > > Is it on purpose that this bugfix hasn't been ported to 4.14? Is it safe > that we backport it manually in our kernel 4.14 builds? Or is the "ext4" > system in 4.14 and 5.4 fundamentally different and this would lead to data > loss or other problems? The commit was over two years ago, so my memory is not going to be perfect. However, Jan had made a comment suggesting the approach in this commit because it should be easier to backport into older stble kernels[1]. "Since proper locking change is going to be a bit more involved, can you perhaps fix this deadlock by just dropping j_checkpoint_mutex in log_do_checkpoint() when we are going to wait for transaction commit. I've checked and that should be fine and that is going to be much easier change to backport into stable kernels..." [1] https://marc.info/?l=linux-ext4&m=154212553014669&w=2 So I suspect it was just that I failed to remember to add a "Cc: stable@kernel.org" and so it was never automatically backported into 4.14 or 4.19. Do you have a reliable reproduction which is triggering the deadlock on your kernels? If so, have you tried applying the patch and does it make the problem go away for you? Cheers, - Ted