From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754907AbbA0XRI (ORCPT ); Tue, 27 Jan 2015 18:17:08 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:35859 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754189AbbA0XRG (ORCPT ); Tue, 27 Jan 2015 18:17:06 -0500 Date: Tue, 27 Jan 2015 15:16:59 -0800 From: "Paul E. McKenney" To: Sasha Levin Cc: Lai Jiangshan , Ingo Molnar , Peter Zijlstra , LKML , "davej@codemonkey.org.uk >> Dave Jones" Subject: Re: rcu, sched: WARNING: CPU: 30 PID: 23771 at kernel/rcu/tree_plugin.h:337 rcu_read_unlock_special+0x369/0x550() Message-ID: <20150127231659.GG19109@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20150123035158.GP9719@linux.vnet.ibm.com> <54C1C7D2.906@oracle.com> <54C1C899.8000106@oracle.com> <20150123065542.GQ9719@linux.vnet.ibm.com> <20150123093644.GA11175@linux.vnet.ibm.com> <54C300DD.9070608@cn.fujitsu.com> <20150124211834.GD9719@linux.vnet.ibm.com> <54C5A184.20105@cn.fujitsu.com> <20150127220329.GF19109@linux.vnet.ibm.com> <54C80C55.2070908@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54C80C55.2070908@oracle.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15012723-0005-0000-0000-0000085B0857 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 27, 2015 at 05:08:21PM -0500, Sasha Levin wrote: > On 01/27/2015 05:03 PM, Paul E. McKenney wrote: > > On Mon, Jan 26, 2015 at 10:08:04AM +0800, Lai Jiangshan wrote: > >> > On 01/25/2015 05:18 AM, Paul E. McKenney wrote: > >> > > >>> > > > >>> > > Good point! In my scenario, CPU 0 would not yet have switched away from > >>> > > Task A. Hmmm... Yet Sasha really does see this failure. Will give it > >>> > > some more thought. > >>> > > > >>> > > Any ideas? > >> > > >> > I don't known which commit was merged from the rcu-git-tree in Sasha's test > >> > I try to review it. > > If I had to guess, it would be 1d082fd06188 (Remove local_irq_disable() > > in rcu_preempt_note_context_switch()), though his finding this might be > > more directly related to increases in trinity's levels of stress. > > Quick update from my end: I've stopped seeing this warning, but I've also stopped > seeing warnings for the other RCU issue I've reported (https://lkml.org/lkml/2015/1/22/676) > so I'm slightly unhappy about that. Another approach would be to remove that patch and then revert 1d082fd06188. Either way, may I have your Tested-by? > >> > We can fallback to git-bitsect if the reviews fails. > > One (very unlikely) possibility is that Sasha's compiler is ignoring the > > barrier() in rcu_preempt_qs(). > > I'm actually running the latest gcc (trunk) as well, so it's very possible that it was > doing something stupid. Hmmmm... Could you please send along the assembly output for rcu_preempt_qs()? Thanx, Paul