From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752465AbdG1PIf (ORCPT ); Fri, 28 Jul 2017 11:08:35 -0400 Received: from mail-qt0-f195.google.com ([209.85.216.195]:38748 "EHLO mail-qt0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752448AbdG1PIc (ORCPT ); Fri, 28 Jul 2017 11:08:32 -0400 Date: Fri, 28 Jul 2017 11:08:28 -0400 From: Tejun Heo To: Michael Bringmann Cc: Lai Jiangshan , linux-kernel@vger.kernel.org, nfont@linux.vnet.ibm.com Subject: Re: [PATCH v7] workqueue: Fix edge cases for calc of pool's cpumask Message-ID: <20170728150828.GM742618@devbig577.frc2.facebook.com> References: <1f06a3f5-ddb6-ee3f-3496-12e081452232@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1f06a3f5-ddb6-ee3f-3496-12e081452232@linux.vnet.ibm.com> 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 On Thu, Jul 27, 2017 at 04:27:14PM -0500, Michael Bringmann wrote: > > There is an underlying assumption/trade-off in many layers of the Linux > system that CPU <-> node mapping is static. This is despite the presence > of features like NUMA and 'hotplug' that support the dynamic addition/ > removal of fundamental system resources like CPUs and memory. PowerPC > systems, however, do provide extensive features for the dynamic change > of resources available to a system. > > Currently, there is little or no synchronization protection around the > updating of the CPU <-> node mapping, and the export/update of this > information for other layers / modules. In systems which can change > this mapping during 'hotplug', like PowerPC, the information is changing > underneath all layers that might reference it. > > This patch attempts to ensure that a valid, usable cpumask attribute is > used by the workqueue infrastructure when setting up new resource pools. > It prevents a crash that has been observed when an 'empty' cpumask is > passed along to the worker/task scheduling code. It is intended as an > intermediate fix until a more fundamental review and correction of the > issue can be done. > > [With additions to the patch provided by Tejun Hao ] > > Signed-off-by: Michael Bringmann Applied to wq/for-4.13-fixes with "fix" replaced with "workaround". Thanks. -- tejun