From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753576Ab2HaBGq (ORCPT ); Thu, 30 Aug 2012 21:06:46 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:53138 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1753082Ab2HaBGp (ORCPT ); Thu, 30 Aug 2012 21:06:45 -0400 X-IronPort-AV: E=Sophos;i="4.80,344,1344182400"; d="scan'208";a="5756467" Message-ID: <50400E86.8090500@cn.fujitsu.com> Date: Fri, 31 Aug 2012 09:08:22 +0800 From: Lai Jiangshan User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc14 Thunderbird/3.1.4 MIME-Version: 1.0 To: Tejun Heo CC: linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/9 V3] workqueue: add non_manager_role_manager_mutex_unlock() References: <1346259120-6216-1-git-send-email-laijs@cn.fujitsu.com> <1346259120-6216-5-git-send-email-laijs@cn.fujitsu.com> <20120829182510.GB2258@dhcp-172-17-108-109.mtv.corp.google.com> <503F2F51.8000301@cn.fujitsu.com> <20120830091739.GA10874@dhcp-172-17-108-109.mtv.corp.google.com> In-Reply-To: <20120830091739.GA10874@dhcp-172-17-108-109.mtv.corp.google.com> X-MIMETrack: Itemize by SMTP Server on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/08/31 09:06:29, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/08/31 09:06:29, Serialize complete at 2012/08/31 09:06:29 Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/30/2012 05:17 PM, Tejun Heo wrote: > Hello, Lai. > > On Thu, Aug 30, 2012 at 05:16:01PM +0800, Lai Jiangshan wrote: >> gcwq_unbind_fn() is unsafe even it is called from a work item. >> so we need non_manager_role_manager_mutex_unlock(). >> >> If rebind_workers() is called from a work item, it is safe when there is >> no CPU_INTENSIVE items. but we can't disable CPU_INTENSIVE items, >> so it is still unsafe, we need non_manager_role_manager_mutex_unlock() too. > > Can you please elaborate? Why is it not safe if there are > CPU_INTENSIVE items? > > Thanks. > Imaging there only two workers, they all have UNBOUND bit because the rebind_workers() has not been called. The First one is processing work items, the second one is idle, when the first one encounter the work item of rebind_workers() and handle it, at the same the second one try to create workers and failed and go to process work items too. but unlikely the second one encounters a CPU_INTENSIVE items, the nr_running is still <=1 after the first one finish rebind_workers(). nr_running. first one: process work item endless +0 or +1 second one: process the CPU_INTENSIVE item endless +0 No one can service for manager role. Thanks. Lai