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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 E6867C55186 for ; Thu, 23 Apr 2020 23:20:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D15BE20784 for ; Thu, 23 Apr 2020 23:20:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729670AbgDWXUQ (ORCPT ); Thu, 23 Apr 2020 19:20:16 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:48652 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728226AbgDWXGe (ORCPT ); Thu, 23 Apr 2020 19:06:34 -0400 Received: from [192.168.4.242] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.89) (envelope-from ) id 1jRkvM-0004c4-1k; Fri, 24 Apr 2020 00:06:28 +0100 Received: from ben by deadeye with local (Exim 4.93) (envelope-from ) id 1jRkvK-00E6jG-EQ; Fri, 24 Apr 2020 00:06:26 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, Denis Kirjanov , "Joe Thornber" , "Mike Snitzer" , "Hou Tao" Date: Fri, 24 Apr 2020 00:04:51 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) X-Patchwork-Hint: ignore Subject: [PATCH 3.16 064/245] dm btree: increase rebalance threshold in __rebalance2() In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.242 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.83-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Hou Tao commit 474e559567fa631dea8fb8407ab1b6090c903755 upstream. We got the following warnings from thin_check during thin-pool setup: $ thin_check /dev/vdb examining superblock examining devices tree missing devices: [1, 84] too few entries in btree_node: 41, expected at least 42 (block 138, max_entries = 126) examining mapping tree The phenomenon is the number of entries in one node of details_info tree is less than (max_entries / 3). And it can be easily reproduced by the following procedures: $ new a thin pool $ presume the max entries of details_info tree is 126 $ new 127 thin devices (e.g. 1~127) to make the root node being full and then split $ remove the first 43 (e.g. 1~43) thin devices to make the children reblance repeatedly $ stop the thin pool $ thin_check The root cause is that the B-tree removal procedure in __rebalance2() doesn't guarantee the invariance: the minimal number of entries in non-root node should be >= (max_entries / 3). Simply fix the problem by increasing the rebalance threshold to make sure the number of entries in each child will be greater than or equal to (max_entries / 3 + 1), so no matter which child is used for removal, the number will still be valid. Signed-off-by: Hou Tao Acked-by: Joe Thornber Signed-off-by: Mike Snitzer Signed-off-by: Ben Hutchings --- drivers/md/persistent-data/dm-btree-remove.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- a/drivers/md/persistent-data/dm-btree-remove.c +++ b/drivers/md/persistent-data/dm-btree-remove.c @@ -203,7 +203,13 @@ static void __rebalance2(struct dm_btree struct btree_node *right = r->n; uint32_t nr_left = le32_to_cpu(left->header.nr_entries); uint32_t nr_right = le32_to_cpu(right->header.nr_entries); - unsigned threshold = 2 * merge_threshold(left) + 1; + /* + * Ensure the number of entries in each child will be greater + * than or equal to (max_entries / 3 + 1), so no matter which + * child is used for removal, the number will still be not + * less than (max_entries / 3). + */ + unsigned int threshold = 2 * (merge_threshold(left) + 1); if (nr_left + nr_right < threshold) { /*