Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755151AbWL3QJr (ORCPT ); Sat, 30 Dec 2006 11:09:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755156AbWL3QJr (ORCPT ); Sat, 30 Dec 2006 11:09:47 -0500 Received: from mail.screens.ru ([213.234.233.54]:34641 "EHLO mail.screens.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755151AbWL3QJq (ORCPT ); Sat, 30 Dec 2006 11:09:46 -0500 Date: Sat, 30 Dec 2006 19:10:31 +0300 From: Oleg Nesterov To: Andrew Morton Cc: Ingo Molnar , David Howells , Christoph Hellwig , Gautham R Shenoy , linux-kernel@vger.kernel.org Subject: [PATCH 3/2] fix flush_workqueue() vs CPU_DEAD race Message-ID: <20061230161031.GA101@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1774 Lines: 49 "[PATCH 1/2] reimplement flush_workqueue()" fixed one race when CPU goes down while flush_cpu_workqueue() plays with it. But there is another problem, CPU can die before flush_workqueue() has a chance to call flush_cpu_workqueue(). In that case pending work_structs can migrate to CPU which was already checked, so we should redo the "for_each_online_cpu(cpu)" loop. Signed-off-by: Oleg Nesterov --- mm-6.20-rc2/kernel/workqueue.c~3_race 2006-12-29 18:37:31.000000000 +0300 +++ mm-6.20-rc2/kernel/workqueue.c 2006-12-30 18:09:07.000000000 +0300 @@ -65,6 +65,7 @@ struct workqueue_struct { /* All the per-cpu workqueues on the system, for hotplug cpu to add/remove threads to each one as cpus come/go. */ +static long hotplug_sequence __read_mostly; static DEFINE_MUTEX(workqueue_mutex); static LIST_HEAD(workqueues); @@ -454,10 +455,16 @@ void fastcall flush_workqueue(struct wor /* Always use first cpu's area. */ flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, singlethread_cpu)); } else { + long sequence; int cpu; +again: + sequence = hotplug_sequence; for_each_online_cpu(cpu) flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu)); + + if (unlikely(sequence != hotplug_sequence)) + goto again; } mutex_unlock(&workqueue_mutex); } @@ -874,6 +881,7 @@ static int __devinit workqueue_cpu_callb cleanup_workqueue_thread(wq, hotcpu); list_for_each_entry(wq, &workqueues, list) take_over_work(wq, hotcpu); + hotplug_sequence++; break; case CPU_LOCK_RELEASE: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/