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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 84432C38A2A for ; Thu, 7 May 2020 20:52:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6698D20735 for ; Thu, 7 May 2020 20:52:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726579AbgEGUv7 (ORCPT ); Thu, 7 May 2020 16:51:59 -0400 Received: from mx2.suse.de ([195.135.220.15]:38380 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726218AbgEGUv6 (ORCPT ); Thu, 7 May 2020 16:51:58 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id C5B5DB13D; Thu, 7 May 2020 20:52:01 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 5DE41DA732; Thu, 7 May 2020 22:51:10 +0200 (CEST) Date: Thu, 7 May 2020 22:51:10 +0200 From: David Sterba To: Qu Wenruo Cc: dsterba@suse.cz, Qu Wenruo , linux-btrfs@vger.kernel.org Subject: Re: [PATCH] btrfs: qgroup: Mark qgroup inconsistent if we're inherting snapshot to a new qgroup Message-ID: <20200507205110.GM18421@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Qu Wenruo , Qu Wenruo , linux-btrfs@vger.kernel.org References: <20200402063735.32808-1-wqu@suse.com> <288d0020-380f-717e-ab05-3fe6dbc64cd5@suse.com> <20200506150448.GH18421@twin.jikos.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Thu, May 07, 2020 at 06:48:24AM +0800, Qu Wenruo wrote: > >>> @@ -2809,6 +2821,8 @@ int btrfs_qgroup_inherit(struct btrfs_trans_handle *trans, u64 srcid, > >>> out: > >>> if (!committing) > >>> mutex_unlock(&fs_info->qgroup_ioctl_lock); > >>> + if (need_rescan) > >>> + fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT; > > > > This got me curious, a non-atomic change to qgroup_flags and without > > any protection. The function is not running in a safe context (like > > quota enable or disable) so lack of synchronization seems suspicious. I > > grepped for other changes to the qgroup_flags and it's very > > inconsistent. Sometimes it's the fs_info::qgroup_lock, no lokcing at all > > or no obvious lock but likely fs_info::qgroup_ioctl_lock or > > qgroup_rescan_lock. > > > > I was considering using atomic bit updates but that would be another > > patch. > > > Isn't the context safe because we're at the commit transaction critical > section? I don't see why, the qgroup_flags could be changed from ioctls, eg. adding a group relation and other places. Without protection the update can race and some of the changes lost.