From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752848AbaETB33 (ORCPT ); Mon, 19 May 2014 21:29:29 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.229]:43113 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751146AbaETB31 (ORCPT ); Mon, 19 May 2014 21:29:27 -0400 Message-ID: <1400549356.10728.22.camel@pippen.local.home> Subject: Re: [patch 2/2] rtmutex: Avoid pointless requeueing in the deadlock detection chain walk From: Steven Rostedt To: Thomas Gleixner Cc: LKML , Lai Jiangshan , Peter Zijlstra , Ingo Molnar Date: Mon, 19 May 2014 21:29:16 -0400 In-Reply-To: References: <20140514195705.618583609@linutronix.de> <20140514200104.670614672@linutronix.de> <20140515130435.24132d1b@gandalf.local.home> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.1-1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-RR-Connecting-IP: 107.14.168.118:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-05-20 at 09:43 +0900, Thomas Gleixner wrote: > In kernel/locking/rtmutex.h: > > > > static inline int debug_rt_mutex_detect_deadlock(struct rt_mutex_waiter *waiter, > > int detect) > > { > > return (waiter != NULL); > > } > > > > Shouldn't that be: return detect || waiter != NULL; > > > > No. We do not care about whether the caller handed in detect or not. Bah, you're right. I was getting confused between try_to_take_rt_mutex() and task_blocks_on_rt_mutex(). The former passes in a NULL waiter when taking the first time, but it's the task_blocks_on_rt_mutex() that does the test, and yes, the waiter is never NULL when boosting. I may send you a patch to add comments to these little idiosyncrasies. > > > > > I know this a separate issue from this patch series, but it's > > something that I just noticed. > > It's not really intuitive. We might make the call sites hand in > constants. RTMUTEX_DETECT_DEADLOCK, RTMUTEX_IGNORE_DEADLOCK or > something like that and switch it depending on > CONFIG_DEBUG_RT_MUTEXES. Yes it is confusing. I use to know this code really well, and now over the years, it's not something to look at quickly and produce a comprehensive response. The sad part is, I looked at it quite a bit before sending my response and I still got confused :-p -- Steve