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=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 0F431C48BE9 for ; Mon, 24 Jun 2019 16:46:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D2CFC20673 for ; Mon, 24 Jun 2019 16:46:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="C3stD53T" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732209AbfFXQq1 (ORCPT ); Mon, 24 Jun 2019 12:46:27 -0400 Received: from mail-qt1-f195.google.com ([209.85.160.195]:41255 "EHLO mail-qt1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730074AbfFXQq1 (ORCPT ); Mon, 24 Jun 2019 12:46:27 -0400 Received: by mail-qt1-f195.google.com with SMTP id d17so15149334qtj.8 for ; Mon, 24 Jun 2019 09:46:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=Dhsef0DXwMLnTfzul4MNZNnoCP5EAjbkYqwXluj+GIs=; b=C3stD53TQJChuMgybngQrezdMqSavx69brZV0iGEaYmGzEDp4tC2VDTxOod8X2pDAi 9JLxxIA/Jnd0Jq9XV+qPRfj4vJblxI8LxUCDxp9AD3/+izgDUqiwRSXr0leO0bC70axA Ep46hqYl2bjIMh8F0ayhG2Sf3mcCIy/OT6lIY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=Dhsef0DXwMLnTfzul4MNZNnoCP5EAjbkYqwXluj+GIs=; b=F8yB7lqUaC2an1o007XETOHKJuE2RJ6/R2yDf2jYHUbvhBetNQ2t9OJL5zjPQBMiRX vyl+PeQjp1KbUrPsB9YOlojLMz8aoSfFV6rOc7dMyCZm5GR8Bw7s96Tubb8BfYVzXhBS MgDEGheqC+dpN+L/IGI12/z5qd4tjSM4c8I8NcHYMNldUVuObPbD4Z6PHFaIg1r051iI tZcMuj0eJMybaobpI2O16um0j9Td1GbmhWuaqqttn6qKXAgUI7eFdMaVvGsEi7ZLo6SN QsjBm0MBC6VeRXybRhCq0QKzZagqZkCBkSkmP8OPhK0bB86xhRbTkIzIx6f/HjtCQVEN gUOA== X-Gm-Message-State: APjAAAV932E1Sk5kiGPbf/biVhysNkEZGBtoul7P0RK98IvnOLKI2+Lb BdMtr5RUUu46TXDh8WslD+yjfQ== X-Google-Smtp-Source: APXvYqxELT3NubfmxXxsRfroMDj0dtbDZl3qf27hvVM29BNgP6+od8/hlgL/ki675ch+A2CFFjfyyQ== X-Received: by 2002:ac8:41d1:: with SMTP id o17mr55923901qtm.17.1561394785988; Mon, 24 Jun 2019 09:46:25 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id x10sm7905346qtc.34.2019.06.24.09.46.25 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Mon, 24 Jun 2019 09:46:25 -0700 (PDT) Date: Mon, 24 Jun 2019 12:46:24 -0400 From: Joel Fernandes To: Byungchul Park Cc: paulmck@linux.ibm.com, 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: <20190624164624.GA41314@google.com> References: <1561364852-5113-1-git-send-email-byungchul.park@lge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1561364852-5113-1-git-send-email-byungchul.park@lge.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. 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 >