From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753081Ab2H3JO0 (ORCPT ); Thu, 30 Aug 2012 05:14:26 -0400 Received: from cn.fujitsu.com ([222.73.24.84]:32534 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751359Ab2H3JOZ (ORCPT ); Thu, 30 Aug 2012 05:14:25 -0400 X-IronPort-AV: E=Sophos;i="4.80,339,1344182400"; d="scan'208";a="5754379" Message-ID: <503F2F51.8000301@cn.fujitsu.com> Date: Thu, 30 Aug 2012 17:16:01 +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> In-Reply-To: <20120829182510.GB2258@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 2012/08/30 17:14:10, Serialize by Router on mailserver/fnst(Release 8.5.3|September 15, 2011) at 2012/08/30 17:14:10, Serialize complete at 2012/08/30 17:14:10 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 02:25 AM, Tejun Heo wrote: > On Thu, Aug 30, 2012 at 12:51:55AM +0800, Lai Jiangshan wrote: >> If hotplug code grabbed the manager_mutex and worker_thread try to create >> a worker, the manage_worker() will return false and worker_thread go to >> process work items. Now, on the CPU, all workers are processing work items, >> no idle_worker left/ready for managing. It breaks the concept of workqueue >> and it is bug. >> >> So when this case happens, the last idle should not go to process work, >> it should go to sleep as usual and wait normal events. but it should >> also be notified by the event that hotplug code release the manager_mutex. >> >> So we add non_manager_role_manager_mutex_unlock() to do this notify. > > Hmmm... how about just running rebind_workers() from a work item? > That way, it would be guaranteed that there alwyas will be an extra > worker available on rebind completion. > > Thanks. > 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. non_manager_role_manager_mutex_unlock() approach is good to fix it. I'm writing V4 patch/approach to fix it too, it is a little more complicated, but it has some benefit over non_manager_role_manager_mutex_unlock() approach. Thanks. Lai