From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753954Ab2IHRLj (ORCPT ); Sat, 8 Sep 2012 13:11:39 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:36187 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751365Ab2IHRLS (ORCPT ); Sat, 8 Sep 2012 13:11:18 -0400 X-IronPort-AV: E=Sophos;i="4.80,392,1344182400"; d="scan'208";a="5807474" From: Lai Jiangshan To: Tejun Heo , linux-kernel@vger.kernel.org Cc: Lai Jiangshan Subject: [PATCH 1/7 V6] workqueue: ensure the wq_worker_sleeping() see the right flags Date: Sun, 9 Sep 2012 01:12:50 +0800 Message-Id: <1347124383-18723-2-git-send-email-laijs@cn.fujitsu.com> X-Mailer: git-send-email 1.7.4.4 In-Reply-To: <1347124383-18723-1-git-send-email-laijs@cn.fujitsu.com> References: <1347124383-18723-1-git-send-email-laijs@cn.fujitsu.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/09/09 01:10:47, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/09/09 01:10:48, Serialize complete at 2012/09/09 01:10:48 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The compiler may compile this code into TWO write/modify instructions. worker->flags &= ~WORKER_UNBOUND; worker->flags |= WORKER_REBIND; so the other CPU may see the temporary of worker->flags which has not WORKER_UNBOUND nor WORKER_REBIND, it will wrongly do local wake up. so we use one write/modify instruction explicitly instead. This bug will not occur on idle workers, because they have another WORKER_NOT_RUNNING flags. Signed-off-by: Lai Jiangshan --- kernel/workqueue.c | 7 +++++-- 1 files changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 85bd340..050b2a5 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1739,10 +1739,13 @@ retry: for_each_busy_worker(worker, i, pos, gcwq) { struct work_struct *rebind_work = &worker->rebind_work; struct workqueue_struct *wq; + unsigned long worker_flags = worker->flags; /* morph UNBOUND to REBIND */ - worker->flags &= ~WORKER_UNBOUND; - worker->flags |= WORKER_REBIND; + worker_flags &= ~WORKER_UNBOUND; + worker_flags |= WORKER_REBIND; + /* ensure the wq_worker_sleeping() see the right flags */ + ACCESS_ONCE(worker->flags) = worker_flags; if (test_and_set_bit(WORK_STRUCT_PENDING_BIT, work_data_bits(rebind_work))) -- 1.7.4.4