From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755290Ab2HNAKM (ORCPT ); Mon, 13 Aug 2012 20:10:12 -0400 Received: from mail-ob0-f174.google.com ([209.85.214.174]:50387 "EHLO mail-ob0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755223Ab2HNAKK (ORCPT ); Mon, 13 Aug 2012 20:10:10 -0400 Date: Mon, 13 Aug 2012 17:10:05 -0700 From: Tejun Heo To: linux-kernel@vger.kernel.org Cc: Oleg Nesterov Subject: [PATCH wq/for-3.7] workqueue: add missing wmb() in clear_work_data() Message-ID: <20120814001005.GI25632@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org >>From 23657bb192f14b789e4c478def8f11ecc95b4f6c Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Mon, 13 Aug 2012 17:08:19 -0700 Any operation which clears PENDING should be preceded by a wmb to guarantee that the next PENDING owner sees all the changes made before PENDING release. There are only two places where PENDING is cleared - set_work_cpu_and_clear_pending() and clear_work_data(). The caller of the former already does smp_wmb() but the latter doesn't have any. Move the wmb above set_work_cpu_and_clear_pending() into it and add one to clear_work_data(). There hasn't been any report related to this issue, and, given how clear_work_data() is used, it is extremely unlikely to have caused any actual problems on any architecture. Signed-off-by: Tejun Heo Cc: Oleg Nesterov --- Fix for another theoretical wmb problem. Will push through wq/for-3.7. Thanks. kernel/workqueue.c | 19 ++++++++++++------- 1 files changed, 12 insertions(+), 7 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 11723c5..4fef952 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -570,11 +570,19 @@ static void set_work_cwq(struct work_struct *work, static void set_work_cpu_and_clear_pending(struct work_struct *work, unsigned int cpu) { + /* + * The following wmb is paired with the implied mb in + * test_and_set_bit(PENDING) and ensures all updates to @work made + * here are visible to and precede any updates by the next PENDING + * owner. + */ + smp_wmb(); set_work_data(work, (unsigned long)cpu << WORK_OFFQ_CPU_SHIFT, 0); } static void clear_work_data(struct work_struct *work) { + smp_wmb(); /* see set_work_cpu_and_clear_pending() */ set_work_data(work, WORK_STRUCT_NO_CPU, 0); } @@ -2182,14 +2190,11 @@ __acquires(&gcwq->lock) wake_up_worker(pool); /* - * Record the last CPU and clear PENDING. The following wmb is - * paired with the implied mb in test_and_set_bit(PENDING) and - * ensures all updates to @work made here are visible to and - * precede any updates by the next PENDING owner. Also, clear - * PENDING inside @gcwq->lock so that PENDING and queued state - * changes happen together while IRQ is disabled. + * Record the last CPU and clear PENDING which should be the last + * update to @work. Also, do this inside @gcwq->lock so that + * PENDING and queued state changes happen together while IRQ is + * disabled. */ - smp_wmb(); set_work_cpu_and_clear_pending(work, gcwq->cpu); spin_unlock_irq(&gcwq->lock); -- 1.7.7.3