From patchwork Wed Mar 26 18:11:26 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Mahoney X-Patchwork-Id: 3894781 Return-Path: X-Original-To: patchwork-linux-btrfs@patchwork.kernel.org Delivered-To: patchwork-parsemail@patchwork2.web.kernel.org Received: from mail.kernel.org (mail.kernel.org [198.145.19.201]) by patchwork2.web.kernel.org (Postfix) with ESMTP id 003AEBF540 for ; Wed, 26 Mar 2014 18:11:36 +0000 (UTC) Received: from mail.kernel.org (localhost [127.0.0.1]) by mail.kernel.org (Postfix) with ESMTP id 27092201C0 for ; Wed, 26 Mar 2014 18:11:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3301B201BC for ; Wed, 26 Mar 2014 18:11:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754732AbaCZSLa (ORCPT ); Wed, 26 Mar 2014 14:11:30 -0400 Received: from cantor2.suse.de ([195.135.220.15]:50731 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750911AbaCZSL3 (ORCPT ); Wed, 26 Mar 2014 14:11:29 -0400 Received: from relay1.suse.de (charybdis-ext.suse.de [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id E9182ABE5 for ; Wed, 26 Mar 2014 18:11:28 +0000 (UTC) Message-ID: <5333184E.3090609@suse.com> Date: Wed, 26 Mar 2014 14:11:26 -0400 From: Jeff Mahoney User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: linux-btrfs Subject: [PATCH] btrfs: fix lockdep warning with reclaim lock inversion X-Enigmail-Version: 1.6 Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org X-Spam-Status: No, score=-7.3 required=5.0 tests=BAYES_00, RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD, UNPARSEABLE_RELAY autolearn=unavailable version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on mail.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP When encountering memory pressure, testers have run into the following lockdep warning. It was caused by __link_block_group calling kobject_add with the groups_sem held. kobject_add calls kvasprintf with GFP_KERNEL, which gets us into reclaim context. The kobject doesn't actually need to be added under the lock -- it just needs to ensure that it's only added for the first block group to be linked. ========================================================= [ INFO: possible irq lock inversion dependency detected ] 3.14.0-rc8-default #1 Not tainted --------------------------------------------------------- kswapd0/169 just changed the state of lock: (&delayed_node->mutex){+.+.-.}, at: [] __btrfs_release_delayed_node+0x3a/0x200 [btrfs] but this lock took another, RECLAIM_FS-unsafe lock in the past: (&found->groups_sem){+++++.} and interrupts could create inverse lock ordering between them. other info that might help us debug this: Possible interrupt unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&found->groups_sem); local_irq_disable(); lock(&delayed_node->mutex); lock(&found->groups_sem); lock(&delayed_node->mutex); *** DEADLOCK *** 2 locks held by kswapd0/169: #0: (shrinker_rwsem){++++..}, at: [] shrink_slab+0x3a/0x160 #1: (&type->s_umount_key#27){++++..}, at: [] grab_super_passive+0x3f/0x90 Signed-off-by: Jeff Mahoney --- fs/btrfs/extent-tree.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -8343,9 +8343,15 @@ static void __link_block_group(struct bt struct btrfs_block_group_cache *cache) { int index = get_block_group_index(cache); + bool first = false; down_write(&space_info->groups_sem); - if (list_empty(&space_info->block_groups[index])) { + if (list_empty(&space_info->block_groups[index])) + first = true; + list_add_tail(&cache->list, &space_info->block_groups[index]); + up_write(&space_info->groups_sem); + + if (first) { struct kobject *kobj = &space_info->block_group_kobjs[index]; int ret; @@ -8357,8 +8363,6 @@ static void __link_block_group(struct bt kobject_put(&space_info->kobj); } } - list_add_tail(&cache->list, &space_info->block_groups[index]); - up_write(&space_info->groups_sem); } static struct btrfs_block_group_cache *