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=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 8CA22C4361B for ; Fri, 4 Dec 2020 17:31:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5F5CE22B40 for ; Fri, 4 Dec 2020 17:31:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729837AbgLDRbJ (ORCPT ); Fri, 4 Dec 2020 12:31:09 -0500 Received: from mx2.suse.de ([195.135.220.15]:33674 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726021AbgLDRbI (ORCPT ); Fri, 4 Dec 2020 12:31:08 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 9D5A1ADCA; Fri, 4 Dec 2020 17:30:27 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 04A73DA7E3; Fri, 4 Dec 2020 18:28:53 +0100 (CET) Date: Fri, 4 Dec 2020 18:28:53 +0100 From: David Sterba To: Qu Wenruo Cc: linux-btrfs@vger.kernel.org Subject: Re: [PATCH] btrfs: qgroup: don't try to wait flushing if we're already holding a transaction Message-ID: <20201204172853.GX6430@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org References: <20201204012448.26546-1-wqu@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201204012448.26546-1-wqu@suse.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Fri, Dec 04, 2020 at 09:24:47AM +0800, Qu Wenruo wrote: > There is a chance of racing for qgroup flushing which may lead to > deadlock: > > Thread A | Thread B > (no trans handler hold) | (already hold a trans handler) > --------------------------------+-------------------------------- > __btrfs_qgroup_reserve_meta() | __btrfs_qgroup_reserve_meta() > |- try_flush_qgroup() | |- try_flushing_qgroup() > |- QGROUP_FLUSHING bit set | | > | | |- test_and_set_bit() > | | |- wait_event() > |- btrfs_join_transaction() | > |- btrfs_commit_transaction()| > > !!! DEAD LOCK !!! > > Since thread A want to commit transaction, but thread B is hold a > transaction handler, blocking the commit. > At the same time, thread B is waiting thread A to finish it commit. > > This is just a hot fix, and would lead to more EDQUOT when we're near > the qgroup limit. > > The root fix would to make all metadata/data reservation to happen > without a transaction handler hold. > > Signed-off-by: Qu Wenruo Added to misc-next, thanks.