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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 54394C4167E for ; Thu, 16 Sep 2021 17:29:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 41D546124D for ; Thu, 16 Sep 2021 17:29:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353132AbhIPRaD (ORCPT ); Thu, 16 Sep 2021 13:30:03 -0400 Received: from mail.kernel.org ([198.145.29.99]:54402 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243724AbhIPQzp (ORCPT ); Thu, 16 Sep 2021 12:55:45 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 16F5861AAD; Thu, 16 Sep 2021 16:30:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631809837; bh=DHfUC0I0hWzaGWI9DCiRXd0dHCLPf74OZNF7j7C50+s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=j4LuxOl61ff2LfEv8ezq1qzj8TvRt//v/lvatHhJcmbt4a0XgrAALbx/frc7QzSs8 8FWrbx7bYcriJYgh5Zr+M+Lk9mxMykrfGL0Za+EtAKEvul+PxOQRpMmLp/CwZ8CMtM Nv1M/7Y43hzV8sVaTnx0OoE8GPkz3UolADQPrsug= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josef Bacik , Filipe Manana , David Sterba , Sasha Levin Subject: [PATCH 5.13 301/380] btrfs: remove racy and unnecessary inode transaction update when using no-holes Date: Thu, 16 Sep 2021 18:00:58 +0200 Message-Id: <20210916155814.298271341@linuxfoundation.org> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210916155803.966362085@linuxfoundation.org> References: <20210916155803.966362085@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Filipe Manana [ Upstream commit cceaa89f02f15f232391ae4be214137b0a0285c0 ] When using the NO_HOLES feature and expanding the size of an inode, we update the inode's last_trans, last_sub_trans and last_log_commit fields at maybe_insert_hole() so that a fsync does know that the inode needs to be logged (by making sure that btrfs_inode_in_log() returns false). This happens for expanding truncate operations, buffered writes, direct IO writes and when cloning extents to an offset greater than the inode's i_size. However the way we do it is racy, because in between setting the inode's last_sub_trans and last_log_commit fields, the log transaction ID that was assigned to last_sub_trans might be committed before we read the root's last_log_commit and assign that value to last_log_commit. If that happens it would make a future call to btrfs_inode_in_log() return true. This is a race that should be extremely unlikely to be hit in practice, and it is the same that was described by commit bc0939fcfab0d7 ("btrfs: fix race between marking inode needs to be logged and log syncing"). The fix would simply be to set last_log_commit to the value we assigned to last_sub_trans minus 1, like it was done in that commit. However updating these two fields plus the last_trans field is pointless here because all the callers of btrfs_cont_expand() (which is the only caller of maybe_insert_hole()) always call btrfs_set_inode_last_trans() or btrfs_update_inode() after calling btrfs_cont_expand(). Calling either btrfs_set_inode_last_trans() or btrfs_update_inode() guarantees that the next fsync will log the inode, as it makes btrfs_inode_in_log() return false. So just remove the code that explicitly sets the inode's last_trans, last_sub_trans and last_log_commit fields. Reviewed-by: Josef Bacik Signed-off-by: Filipe Manana Signed-off-by: David Sterba Signed-off-by: Sasha Levin --- fs/btrfs/inode.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index c3810c6430d9..044300db5e22 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -5064,15 +5064,13 @@ static int maybe_insert_hole(struct btrfs_root *root, struct btrfs_inode *inode, int ret; /* - * Still need to make sure the inode looks like it's been updated so - * that any holes get logged if we fsync. + * If NO_HOLES is enabled, we don't need to do anything. + * Later, up in the call chain, either btrfs_set_inode_last_sub_trans() + * or btrfs_update_inode() will be called, which guarantee that the next + * fsync will know this inode was changed and needs to be logged. */ - if (btrfs_fs_incompat(fs_info, NO_HOLES)) { - inode->last_trans = fs_info->generation; - inode->last_sub_trans = root->log_transid; - inode->last_log_commit = root->last_log_commit; + if (btrfs_fs_incompat(fs_info, NO_HOLES)) return 0; - } /* * 1 - for the one we're dropping -- 2.30.2