From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752556AbdGRWl5 (ORCPT ); Tue, 18 Jul 2017 18:41:57 -0400 Received: from mail-qt0-f194.google.com ([209.85.216.194]:36737 "EHLO mail-qt0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751882AbdGRWl4 (ORCPT ); Tue, 18 Jul 2017 18:41:56 -0400 Date: Tue, 18 Jul 2017 18:41:52 -0400 From: Tejun Heo To: Christoph Hellwig Cc: Alexei Potashnik , linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: [PATCH wq/for-4.13-fixes] workqueue: restore WQ_UNBOUND/max_active==1 to be ordered Message-ID: <20170718224152.GJ3365493@devbig577.frc2.facebook.com> References: <20170718191829.GA11583@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170718191829.GA11583@infradead.org> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The combination of WQ_UNBOUND and max_active == 1 used to imply ordered execution. After NUMA affinity 4c16bd327c74 ("workqueue: implement NUMA affinity for unbound workqueues"), this is no longer true due to per-node worker pools. While the right way to create an ordered workqueue is alloc_ordered_workqueue(), the documentation has been misleading for a long time and people do use WQ_UNBOUND and max_active == 1 for ordered workqueues which can lead to subtle bugs which are very difficult to trigger. It's unlikely that we'd see noticeable performance impact by enforcing ordering on WQ_UNBOUND / max_active == 1 workqueues. Let's automatically set __WQ_ORDERED for those workqueues. Signed-off-by: Tejun Heo Reported-by: Christoph Hellwig Reported-by: Alexei Potashnik Fixes: 4c16bd327c74 ("workqueue: implement NUMA affinity for unbound workqueues") Cc: stable@vger.kernel.org # v3.10+ --- Hello, Unless somebody objects, I'll apply this to wq/for-4.13-fixes. Thanks. kernel/workqueue.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index a86688f..abe4a49 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3929,6 +3929,16 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt, struct workqueue_struct *wq; struct pool_workqueue *pwq; + /* + * Unbound && max_active == 1 used to imply ordered, which is no + * longer the case on NUMA machines due to per-node pools. While + * alloc_ordered_workqueue() is the right way to create an ordered + * workqueue, keep the previous behavior to avoid subtle breakages + * on NUMA. + */ + if ((flags & WQ_UNBOUND) && max_active == 1) + flags |= __WQ_ORDERED; + /* see the comment above the definition of WQ_POWER_EFFICIENT */ if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient) flags |= WQ_UNBOUND;