Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753827AbcKYIf6 (ORCPT ); Fri, 25 Nov 2016 03:35:58 -0500 Received: from mx2.suse.de ([195.135.220.15]:45357 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752658AbcKYIdK (ORCPT ); Fri, 25 Nov 2016 03:33:10 -0500 X-Amavis-Alert: BAD HEADER SECTION, Duplicate header field: "References" From: Jiri Slaby To: stable@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Hugh Dickins , Tejun Heo , Jiri Slaby Subject: [PATCH 3.12 118/127] cgroup: use an ordered workqueue for cgroup destruction Date: Fri, 25 Nov 2016 09:30:31 +0100 Message-Id: <58563cf6ff3ad14d9f08cd7ccb0656e7fe3872ef.1480062521.git.jslaby@suse.cz> X-Mailer: git-send-email 2.10.2 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2178 Lines: 56 From: Hugh Dickins 3.12-stable review patch. If anyone has any objections, please let me know. =============== commit ab3f5faa6255a0eb4f832675507d9e295ca7e9ba upstream. Sometimes the cleanup after memcg hierarchy testing gets stuck in mem_cgroup_reparent_charges(), unable to bring non-kmem usage down to 0. There may turn out to be several causes, but a major cause is this: the workitem to offline parent can get run before workitem to offline child; parent's mem_cgroup_reparent_charges() circles around waiting for the child's pages to be reparented to its lrus, but it's holding cgroup_mutex which prevents the child from reaching its mem_cgroup_reparent_charges(). Just use an ordered workqueue for cgroup_destroy_wq. tj: Committing as the temporary fix until the reverse dependency can be removed from memcg. Comment updated accordingly. Fixes: e5fca243abae ("cgroup: use a dedicated workqueue for cgroup destruction") Suggested-by: Filipe Brandenburger Signed-off-by: Hugh Dickins Signed-off-by: Tejun Heo Signed-off-by: Jiri Slaby --- kernel/cgroup.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 5d9d542c0bb5..e89f6cec01c9 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -5168,12 +5168,16 @@ static int __init cgroup_wq_init(void) /* * There isn't much point in executing destruction path in * parallel. Good chunk is serialized with cgroup_mutex anyway. - * Use 1 for @max_active. + * + * XXX: Must be ordered to make sure parent is offlined after + * children. The ordering requirement is for memcg where a + * parent's offline may wait for a child's leading to deadlock. In + * the long term, this should be fixed from memcg side. * * We would prefer to do this in cgroup_init() above, but that * is called before init_workqueues(): so leave this until after. */ - cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1); + cgroup_destroy_wq = alloc_ordered_workqueue("cgroup_destroy", 0); BUG_ON(!cgroup_destroy_wq); return 0; } -- 2.10.2