From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752333AbcBJPzH (ORCPT ); Wed, 10 Feb 2016 10:55:07 -0500 Received: from mail-yk0-f193.google.com ([209.85.160.193]:34310 "EHLO mail-yk0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751333AbcBJPzE (ORCPT ); Wed, 10 Feb 2016 10:55:04 -0500 Date: Wed, 10 Feb 2016 10:55:03 -0500 From: Tejun Heo To: Mike Galbraith Cc: LKML Subject: [PATCH wq/for-4.5-fixes] workqueue: handle NUMA_NO_NODE for unbound pool_workqueue lookup Message-ID: <20160210155503.GE3741@mtj.duckdns.org> References: <1454424264.11183.46.camel@gmail.com> <20160203185425.GK14091@mtj.duckdns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160203185425.GK14091@mtj.duckdns.org> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, With 874bbfe600a6 reverted, this doesn't matter as much but I'm still committing it to wq/for-4.5-fixes. The commit message has been updated accordingly. Thanks. ------ 8< ------ >>From 9354baa208f47bf088c28c1da5f38abe172db5d6 Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Wed, 3 Feb 2016 13:54:25 -0500 When looking up the pool_workqueue to use for an unbound workqueue, workqueue assumes that the target CPU is always bound to a valid NUMA node. However, currently, when a CPU goes offline, the mapping is destroyed and cpu_to_node() returns NUMA_NO_NODE. This has always been broken but hasn't triggered often enough before 874bbfe600a6 ("workqueue: make sure delayed work run in local cpu"). After the commit, workqueue forcifully assigns the local CPU for delayed work items without explicit target CPU to fix a different issue. This widens the window where CPU can go offline while a delayed work item is pending causing delayed work items dispatched with target CPU set to an already offlined CPU. The resulting NUMA_NO_NODE mapping makes workqueue try to queue the work item on a NULL pool_workqueue and thus crash. While 874bbfe600a6 has been reverted for a different reason making the bug less visible again, it can still happen. Fix it by mapping NUMA_NO_NODE to the default pool_workqueue from unbound_pwq_by_node(). This is a temporary workaround. The long term solution is keeping CPU -> NODE mapping stable across CPU off/online cycles which is being worked on. Signed-off-by: Tejun Heo Reported-by: Mike Galbraith Cc: Tang Chen Cc: Rafael J. Wysocki Cc: Len Brown Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/g/1454424264.11183.46.camel@gmail.com Link: http://lkml.kernel.org/g/1453702100-2597-1-git-send-email-tangchen@cn.fujitsu.com --- kernel/workqueue.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index dc7faad..3ca7ab8 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -570,6 +570,16 @@ static struct pool_workqueue *unbound_pwq_by_node(struct workqueue_struct *wq, int node) { assert_rcu_or_wq_mutex_or_pool_mutex(wq); + + /* + * XXX: @node can be NUMA_NO_NODE if CPU goes offline while a + * delayed item is pending. The plan is to keep CPU -> NODE + * mapping valid and stable across CPU on/offlines. Once that + * happens, this workaround can be removed. + */ + if (unlikely(node == NUMA_NO_NODE)) + return wq->dfl_pwq; + return rcu_dereference_raw(wq->numa_pwq_tbl[node]); } -- 2.5.0