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=-9.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 64D33C43461 for ; Fri, 11 Sep 2020 14:15:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2BFE822276 for ; Fri, 11 Sep 2020 14:15:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599833703; bh=svXOEzPwRsOn0YI0r7BxwC0NFoM3u0CxMt9i8WkVgH4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=yQhpI+WwXjWL0fz/ok/VyMTO7kojC2mujSErcXKS+mucXTfiawUYyGOVb6GGq6wEe +Ha/AmsYi3CR3ibPL/oAOnCwrveIplS8j57LGRGIUg0BwKU0B3OsWl5q02Kch6oGN1 rTOqAzGgIvFnIgMYJEq8SKcHBeSltCvIANibJ4r8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726144AbgIKNO2 (ORCPT ); Fri, 11 Sep 2020 09:14:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:49906 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726102AbgIKM6D (ORCPT ); Fri, 11 Sep 2020 08:58:03 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 9F0CF22224; Fri, 11 Sep 2020 12:55:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1599828928; bh=svXOEzPwRsOn0YI0r7BxwC0NFoM3u0CxMt9i8WkVgH4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ca93ihv4rvVaCGLaDDq1gK9uswGZXub9ToYRU69uzPC8lYvhMB/T5ahG2Ek5RUsC4 xpGPaJiyczckn1j29KFfc0pFKMkBGPPZtmP/5RMyC88P0aZ+SsXQE6tKPV94luRnBW 3w/gbqD/JqnrEK+27h96RT5xgNtUwVc3q5LAjoVo= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Filipe Manana , Josef Bacik , David Sterba Subject: [PATCH 4.4 22/62] btrfs: drop path before adding new uuid tree entry Date: Fri, 11 Sep 2020 14:46:05 +0200 Message-Id: <20200911122503.503512875@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200911122502.395450276@linuxfoundation.org> References: <20200911122502.395450276@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Josef Bacik commit 9771a5cf937129307d9f58922d60484d58ababe7 upstream. With the conversion of the tree locks to rwsem I got the following lockdep splat: ====================================================== WARNING: possible circular locking dependency detected 5.8.0-rc7-00167-g0d7ba0c5b375-dirty #925 Not tainted ------------------------------------------------------ btrfs-uuid/7955 is trying to acquire lock: ffff88bfbafec0f8 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180 but task is already holding lock: ffff88bfbafef2a8 (btrfs-uuid-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (btrfs-uuid-00){++++}-{3:3}: down_read_nested+0x3e/0x140 __btrfs_tree_read_lock+0x39/0x180 __btrfs_read_lock_root_node+0x3a/0x50 btrfs_search_slot+0x4bd/0x990 btrfs_uuid_tree_add+0x89/0x2d0 btrfs_uuid_scan_kthread+0x330/0x390 kthread+0x133/0x150 ret_from_fork+0x1f/0x30 -> #0 (btrfs-root-00){++++}-{3:3}: __lock_acquire+0x1272/0x2310 lock_acquire+0x9e/0x360 down_read_nested+0x3e/0x140 __btrfs_tree_read_lock+0x39/0x180 __btrfs_read_lock_root_node+0x3a/0x50 btrfs_search_slot+0x4bd/0x990 btrfs_find_root+0x45/0x1b0 btrfs_read_tree_root+0x61/0x100 btrfs_get_root_ref.part.50+0x143/0x630 btrfs_uuid_tree_iterate+0x207/0x314 btrfs_uuid_rescan_kthread+0x12/0x50 kthread+0x133/0x150 ret_from_fork+0x1f/0x30 other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(btrfs-uuid-00); lock(btrfs-root-00); lock(btrfs-uuid-00); lock(btrfs-root-00); *** DEADLOCK *** 1 lock held by btrfs-uuid/7955: #0: ffff88bfbafef2a8 (btrfs-uuid-00){++++}-{3:3}, at: __btrfs_tree_read_lock+0x39/0x180 stack backtrace: CPU: 73 PID: 7955 Comm: btrfs-uuid Kdump: loaded Not tainted 5.8.0-rc7-00167-g0d7ba0c5b375-dirty #925 Hardware name: Quanta Tioga Pass Single Side 01-0030993006/Tioga Pass Single Side, BIOS F08_3A18 12/20/2018 Call Trace: dump_stack+0x78/0xa0 check_noncircular+0x165/0x180 __lock_acquire+0x1272/0x2310 lock_acquire+0x9e/0x360 ? __btrfs_tree_read_lock+0x39/0x180 ? btrfs_root_node+0x1c/0x1d0 down_read_nested+0x3e/0x140 ? __btrfs_tree_read_lock+0x39/0x180 __btrfs_tree_read_lock+0x39/0x180 __btrfs_read_lock_root_node+0x3a/0x50 btrfs_search_slot+0x4bd/0x990 btrfs_find_root+0x45/0x1b0 btrfs_read_tree_root+0x61/0x100 btrfs_get_root_ref.part.50+0x143/0x630 btrfs_uuid_tree_iterate+0x207/0x314 ? btree_readpage+0x20/0x20 btrfs_uuid_rescan_kthread+0x12/0x50 kthread+0x133/0x150 ? kthread_create_on_node+0x60/0x60 ret_from_fork+0x1f/0x30 This problem exists because we have two different rescan threads, btrfs_uuid_scan_kthread which creates the uuid tree, and btrfs_uuid_tree_iterate that goes through and updates or deletes any out of date roots. The problem is they both do things in different order. btrfs_uuid_scan_kthread() reads the tree_root, and then inserts entries into the uuid_root. btrfs_uuid_tree_iterate() scans the uuid_root, but then does a btrfs_get_fs_root() which can read from the tree_root. It's actually easy enough to not be holding the path in btrfs_uuid_scan_kthread() when we add a uuid entry, as we already drop it further down and re-start the search when we loop. So simply move the path release before we add our entry to the uuid tree. This also fixes a problem where we're holding a path open after we do btrfs_end_transaction(), which has it's own problems. CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Filipe Manana Signed-off-by: Josef Bacik Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Greg Kroah-Hartman --- fs/btrfs/volumes.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -4065,6 +4065,7 @@ static int btrfs_uuid_scan_kthread(void goto skip; } update_tree: + btrfs_release_path(path); if (!btrfs_is_empty_uuid(root_item.uuid)) { ret = btrfs_uuid_tree_add(trans, fs_info->uuid_root, root_item.uuid, @@ -4090,6 +4091,7 @@ update_tree: } skip: + btrfs_release_path(path); if (trans) { ret = btrfs_end_transaction(trans, fs_info->uuid_root); trans = NULL; @@ -4097,7 +4099,6 @@ skip: break; } - btrfs_release_path(path); if (key.offset < (u64)-1) { key.offset++; } else if (key.type < BTRFS_ROOT_ITEM_KEY) {