From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C7BB5C48BD6 for ; Tue, 25 Jun 2019 13:25:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9F7F6208CA for ; Tue, 25 Jun 2019 13:25:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728658AbfFYNZJ (ORCPT ); Tue, 25 Jun 2019 09:25:09 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:38636 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726486AbfFYNZJ (ORCPT ); Tue, 25 Jun 2019 09:25:09 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x5PDHbGQ053055; Tue, 25 Jun 2019 09:24:35 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0b-001b2d01.pphosted.com with ESMTP id 2tbk6241m9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 25 Jun 2019 09:24:35 -0400 Received: from m0098414.ppops.net (m0098414.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x5PDHlRT054117; Tue, 25 Jun 2019 09:24:34 -0400 Received: from ppma04dal.us.ibm.com (7a.29.35a9.ip4.static.sl-reverse.com [169.53.41.122]) by mx0b-001b2d01.pphosted.com with ESMTP id 2tbk6241kd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 25 Jun 2019 09:24:34 -0400 Received: from pps.filterd (ppma04dal.us.ibm.com [127.0.0.1]) by ppma04dal.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x5PDK5Dd008348; Tue, 25 Jun 2019 13:24:33 GMT Received: from b01cxnp22033.gho.pok.ibm.com (b01cxnp22033.gho.pok.ibm.com [9.57.198.23]) by ppma04dal.us.ibm.com with ESMTP id 2t9by6ra34-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Tue, 25 Jun 2019 13:24:33 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22033.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x5PDOWUG49152280 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 25 Jun 2019 13:24:32 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7E405B206A; Tue, 25 Jun 2019 13:24:32 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 50090B2064; Tue, 25 Jun 2019 13:24:32 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.26]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 25 Jun 2019 13:24:32 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 4328E16C179D; Tue, 25 Jun 2019 06:24:32 -0700 (PDT) Date: Tue, 25 Jun 2019 06:24:32 -0700 From: "Paul E. McKenney" To: Byungchul Park Cc: Joel Fernandes , josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@lge.com Subject: Re: [RFC] rcu: Warn that rcu ktheads cannot be spawned Message-ID: <20190625132432.GU26519@linux.ibm.com> Reply-To: paulmck@linux.ibm.com References: <1561364852-5113-1-git-send-email-byungchul.park@lge.com> <20190624164624.GA41314@google.com> <20190625025015.GB10912@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190625025015.GB10912@X58A-UD3R> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-25_10:,, 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 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906250104 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 25, 2019 at 11:50:15AM +0900, Byungchul Park wrote: > On Mon, Jun 24, 2019 at 12:46:24PM -0400, Joel Fernandes wrote: > > On Mon, Jun 24, 2019 at 05:27:32PM +0900, Byungchul Park wrote: > > > Hello rcu folks, > > > > > > I thought it'd better to announce it if those spawnings fail because of > > > !rcu_scheduler_fully_active. > > > > > > Of course, with the current code, it never happens though. > > > > > > Thoughts? > > > > It seems in the right spirit, but with your patch a warning always fires. > > rcu_prepare_cpu() is called multiple times, once from rcu_init() and then > > from hotplug paths. > > I'm sorry bothering you. > > I sent the patch to ask how you guys think about the direction coz I'm > not sure if the current code w/o warning on it is intended or not. > > However from now on, I think I need to test it first even if it's RFC :) That is what I do. ;-) Thanx, Paul > Thank you very much for the information. > > Thanks, > Byungchul > > > Warning splat stack looks like: > > > > [ 0.398767] Call Trace: > > [ 0.398775] rcu_init+0x6aa/0x724 > > [ 0.398779] start_kernel+0x220/0x4a2 > > [ 0.398780] ? copy_bootdata+0x12/0xac > > [ 0.398782] secondary_startup_64+0xa4/0xb0 > > > > > > > > > > Thanks, > > > Byungchul > > > > > > ---8<--- > > > From 58a33a85c70f82c406319b4752af95cf6ceb73a3 Mon Sep 17 00:00:00 2001 > > > From: Byungchul Park > > > Date: Mon, 24 Jun 2019 17:08:26 +0900 > > > Subject: [RFC] rcu: Warn that rcu ktheads cannot be spawned > > > > > > In case that rcu ktheads cannot be spawned due to > > > !rcu_scheduler_fully_active, it'd be better to anounce it. > > > > > > While at it, because the return value of rcu_spawn_one_boost_kthread() > > > is not used any longer, changed the return type from int to void. > > > > > > Signed-off-by: Byungchul Park > > > --- > > > kernel/rcu/tree_plugin.h | 31 +++++++++++++++++++------------ > > > 1 file changed, 19 insertions(+), 12 deletions(-) > > > > > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > > > index 1102765..7d74193 100644 > > > --- a/kernel/rcu/tree_plugin.h > > > +++ b/kernel/rcu/tree_plugin.h > > > @@ -1131,7 +1131,7 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) > > > * already exist. We only create this kthread for preemptible RCU. > > > * Returns zero if all is well, a negated errno otherwise. > > > */ > > > -static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp) > > > +static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) > > > { > > > int rnp_index = rnp - rcu_get_root(); > > > unsigned long flags; > > > @@ -1139,25 +1139,24 @@ static int rcu_spawn_one_boost_kthread(struct rcu_node *rnp) > > > struct task_struct *t; > > > > > > if (!IS_ENABLED(CONFIG_PREEMPT_RCU)) > > > - return 0; > > > + return; > > > > > > - if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0) > > > - return 0; > > > + if (rcu_rnp_online_cpus(rnp) == 0) > > > + return; > > > > > > rcu_state.boost = 1; > > > if (rnp->boost_kthread_task != NULL) > > > - return 0; > > > + return; > > > t = kthread_create(rcu_boost_kthread, (void *)rnp, > > > "rcub/%d", rnp_index); > > > if (IS_ERR(t)) > > > - return PTR_ERR(t); > > > + return; > > > raw_spin_lock_irqsave_rcu_node(rnp, flags); > > > rnp->boost_kthread_task = t; > > > raw_spin_unlock_irqrestore_rcu_node(rnp, flags); > > > sp.sched_priority = kthread_prio; > > > sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); > > > wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ > > > - return 0; > > > } > > > > > > static void rcu_cpu_kthread_setup(unsigned int cpu) > > > @@ -1264,8 +1263,12 @@ static void __init rcu_spawn_boost_kthreads(void) > > > per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0; > > > if (WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcub kthread, OOM is now expected behavior\n", __func__)) > > > return; > > > + > > > + if (WARN_ON(!rcu_scheduler_fully_active)) > > > + return; > > > + > > > rcu_for_each_leaf_node(rnp) > > > - (void)rcu_spawn_one_boost_kthread(rnp); > > > + rcu_spawn_one_boost_kthread(rnp); > > > } > > > > > > static void rcu_prepare_kthreads(int cpu) > > > @@ -1273,9 +1276,11 @@ static void rcu_prepare_kthreads(int cpu) > > > struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); > > > struct rcu_node *rnp = rdp->mynode; > > > > > > + if (WARN_ON(!rcu_scheduler_fully_active)) > > > + return; > > > + > > > /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ > > > - if (rcu_scheduler_fully_active) > > > - (void)rcu_spawn_one_boost_kthread(rnp); > > > + rcu_spawn_one_boost_kthread(rnp); > > > } > > > > > > #else /* #ifdef CONFIG_RCU_BOOST */ > > > @@ -2198,8 +2203,10 @@ static void rcu_spawn_one_nocb_kthread(int cpu) > > > */ > > > static void rcu_spawn_cpu_nocb_kthread(int cpu) > > > { > > > - if (rcu_scheduler_fully_active) > > > - rcu_spawn_one_nocb_kthread(cpu); > > > + if (WARN_ON(!rcu_scheduler_fully_active)) > > > + return; > > > + > > > + rcu_spawn_one_nocb_kthread(cpu); > > > } > > > > > > /* > > > -- > > > 1.9.1 > > > >