From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752772Ab2G0Xza (ORCPT ); Fri, 27 Jul 2012 19:55:30 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:47011 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752454Ab2G0XzW (ORCPT ); Fri, 27 Jul 2012 19:55:22 -0400 From: Tejun Heo To: linux-kernel@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, padovan@profusion.mobi, marcel@holtmann.org, peterz@infradead.org, mingo@redhat.com, davem@davemloft.net, dougthompson@xmission.com, ibm-acpi@hmh.eng.br, cbou@mail.ru, rui.zhang@intel.com, Tejun Heo , Oleg Nesterov , stable@vger.kernel.org Subject: [PATCH 03/15] workqueue: add missing smp_wmb() in process_one_work() Date: Fri, 27 Jul 2012 16:54:56 -0700 Message-Id: <1343433308-26614-4-git-send-email-tj@kernel.org> X-Mailer: git-send-email 1.7.7.3 In-Reply-To: <1343433308-26614-1-git-send-email-tj@kernel.org> References: <1343433308-26614-1-git-send-email-tj@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org WORK_STRUCT_PENDING is used to claim ownership of a work item and process_one_work() releases it before starting execution. When someone else grabs PENDING, all pre-release updates to the work item should be visible and all updates made by the new owner should happen afterwards. Grabbing PENDING uses test_and_set_bit() and thus has a full barrier; however, clearing doesn't have a matching wmb. Given the preceding spin_unlock and use of clear_bit, I don't believe this can be a problem on an actual machine and there hasn't been any related report but it still is theretically possible for clear_pending to permeate upwards and happen before work->entry update. Add an explicit smp_wmb() before work_clear_pending(). Signed-off-by: Tejun Heo Cc: Oleg Nesterov Cc: stable@vger.kernel.org --- kernel/workqueue.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 70f95ab..5c26d36 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1997,7 +1997,9 @@ __acquires(&gcwq->lock) spin_unlock_irq(&gcwq->lock); + smp_wmb(); /* paired with test_and_set_bit(PENDING) */ work_clear_pending(work); + lock_map_acquire_read(&cwq->wq->lockdep_map); lock_map_acquire(&lockdep_map); trace_workqueue_execute_start(work); -- 1.7.7.3