From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761870AbaGRNMq (ORCPT ); Fri, 18 Jul 2014 09:12:46 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:44510 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1761848AbaGRNMm (ORCPT ); Fri, 18 Jul 2014 09:12:42 -0400 Message-ID: <53C91CA9.7060103@oracle.com> Date: Fri, 18 Jul 2014 09:10:01 -0400 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: paulmck@linux.vnet.ibm.com CC: linux-kernel@vger.kernel.org, mingo@kernel.org, laijs@cn.fujitsu.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, sbw@mit.edu, linux-rt-users@vger.kernel.org Subject: Re: [PATCH RFC tip/core/rcu 2/2] rcu: Create rcuo kthreads only for onlined CPUs References: <20140714100604.GA9905@linux.vnet.ibm.com> <1405332404-10094-1-git-send-email-paulmck@linux.vnet.ibm.com> <1405332404-10094-2-git-send-email-paulmck@linux.vnet.ibm.com> <53C9023D.3090007@oracle.com> <20140718125516.GH8690@linux.vnet.ibm.com> In-Reply-To: <20140718125516.GH8690@linux.vnet.ibm.com> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Source-IP: ucsinet21.oracle.com [156.151.31.93] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/18/2014 08:55 AM, Paul E. McKenney wrote: > On Fri, Jul 18, 2014 at 07:17:17AM -0400, Sasha Levin wrote: >> > On 07/14/2014 06:06 AM, Paul E. McKenney wrote: >>> > > From: "Paul E. McKenney" >>> > > >>> > > RCU currently uses for_each_possible_cpu() to spawn rcuo kthreads, >>> > > which can result in more rcuo kthreads than one would expect, for >>> > > example, derRichard reported 64 CPUs worth of rcuo kthreads on an >>> > > 8-CPU image. This commit therefore creates rcuo kthreads only for >>> > > those CPUs that actually come online. >>> > > >>> > > Reported-by: derRichard >>> > > Signed-off-by: Paul E. McKenney >> > >> > Hey Paul, >> > >> > Me again. :) >> > >> > It seems that this patch moved thread initialization to a point way >> > too early during boot, before rest_init() which initializes kthreadd_task >> > runs, so creating a new kthread triggers a NULL ptr deref: > This should be fixed by commit 918179699e4a in -rcu. My guess is that > you are instead using commit c6e2955266d14, which, said to say, made it > into -next yesterday. :-( > > If my guess is wrong, please let me know! Your guess is correct. I'll wait for the next -next tree and retry. Thanks, Sasha