From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751271AbeECRRg (ORCPT ); Thu, 3 May 2018 13:17:36 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:59988 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750947AbeECRRe (ORCPT ); Thu, 3 May 2018 13:17:34 -0400 Date: Thu, 3 May 2018 10:18:50 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Mike Galbraith , Matt Fleming , Ingo Molnar , linux-kernel@vger.kernel.org, Michal Hocko Subject: Re: cpu stopper threads and load balancing leads to deadlock Reply-To: paulmck@linux.vnet.ibm.com References: <1525349542.9956.2.camel@gmx.de> <20180503122808.GZ12217@hirez.programming.kicks-ass.net> <1525351221.9956.4.camel@gmx.de> <20180503124943.GB12217@hirez.programming.kicks-ass.net> <1525354359.5576.1.camel@gmx.de> <20180503135617.GC12217@hirez.programming.kicks-ass.net> <1525357015.5577.2.camel@gmx.de> <20180503144450.GD12217@hirez.programming.kicks-ass.net> <20180503161231.GI26088@linux.vnet.ibm.com> <20180503164508.GG12217@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180503164508.GG12217@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18050317-0036-0000-0000-000002EED514 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008963; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000258; SDB=6.01026980; UDB=6.00524556; IPR=6.00806113; MB=3.00020910; MTD=3.00000008; XFM=3.00000015; UTC=2018-05-03 17:17:30 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18050317-0037-0000-0000-000044342BE1 Message-Id: <20180503171850.GL26088@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-05-03_08:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1805030149 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 03, 2018 at 06:45:08PM +0200, Peter Zijlstra wrote: > On Thu, May 03, 2018 at 09:12:31AM -0700, Paul E. McKenney wrote: > > On Thu, May 03, 2018 at 04:44:50PM +0200, Peter Zijlstra wrote: > > > On Thu, May 03, 2018 at 04:16:55PM +0200, Mike Galbraith wrote: > > > > On Thu, 2018-05-03 at 15:56 +0200, Peter Zijlstra wrote: > > > > > On Thu, May 03, 2018 at 03:32:39PM +0200, Mike Galbraith wrote: > > > > > > > > > > > Dang. With $subject fix applied as well.. > > > > > > > > > > That's a NO then... :-( > > > > > > > > Could say who cares about oddball offline wakeup stat. > > > > > > Yeah, nobody.. but I don't want to have to change the wakeup code to > > > deal with this if at all possible. That'd just add conditions that are > > > 'always' false, except in this exceedingly rare circumstance. > > > > > > So ideally we manage to tell RCU that it needs to pay attention while > > > we're doing this here thing, which is what I thought RCU_NONIDLE() was > > > about. > > > > One straightforward approach would be to provide a arch-specific > > Kconfig option that tells notify_cpu_starting() not to bother invoking > > rcu_cpu_starting(). Then x86 selects this Kconfig option and invokes > > rcu_cpu_starting() itself early enough to avoid splats. > > > > See the (untested, probably does not even build) patch below. > > > > I have no idea where to insert either the "select" or the call to > > rcu_cpu_starting(), so I left those out. I know that putting the > > call too early will cause trouble, but I have no idea what constitutes > > "too early". :-/ > > Something like so perhaps? Mike, can you play around with that? Could > burn your granny and eat your cookies. > > > diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c > index 7468de429087..07360523c3ce 100644 > --- a/arch/x86/kernel/cpu/mtrr/main.c > +++ b/arch/x86/kernel/cpu/mtrr/main.c > @@ -793,6 +793,9 @@ void mtrr_ap_init(void) > > if (!use_intel() || mtrr_aps_delayed_init) > return; > + > + rcu_cpu_starting(smp_processor_id()); > + > /* > * Ideally we should hold mtrr_mutex here to avoid mtrr entries > * changed, but this routine will be called in cpu boot time, > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 2a734692a581..4dab46950fdb 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -3775,6 +3775,8 @@ int rcutree_dead_cpu(unsigned int cpu) > return 0; > } > > +static DEFINE_PER_CPU(int, rcu_cpu_started); > + > /* > * Mark the specified CPU as being online so that subsequent grace periods > * (both expedited and normal) will wait on it. Note that this means that > @@ -3796,6 +3798,11 @@ void rcu_cpu_starting(unsigned int cpu) > struct rcu_node *rnp; > struct rcu_state *rsp; > > + if (per_cpu(rcu_cpu_started, cpu)) I would log a non-splat dmesg the first time this happened, just for my future sanity, but otherwise looks fine. I am a bit concerned about calls to rcu_cpu_starting() getting sprinkled all through the code. Or am I being excessively paranoid? Thanx, Paul > + return; > + > + per_cpu(rcu_cpu_started, cpu) = 1; > + > for_each_rcu_flavor(rsp) { > rdp = per_cpu_ptr(rsp->rda, cpu); > rnp = rdp->mynode; > @@ -3852,6 +3859,8 @@ void rcu_report_dead(unsigned int cpu) > preempt_enable(); > for_each_rcu_flavor(rsp) > rcu_cleanup_dying_idle_cpu(cpu, rsp); > + > + per_cpu(rcu_cpu_started, cpu) = 0; > } > > /* Migrate the dead CPU's callbacks to the current CPU. */ >