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=-8.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 D31A5C43613 for ; Mon, 24 Jun 2019 08:58:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B61292083D for ; Mon, 24 Jun 2019 08:58:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728022AbfFXI6L (ORCPT ); Mon, 24 Jun 2019 04:58:11 -0400 Received: from lgeamrelo12.lge.com ([156.147.23.52]:50340 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725916AbfFXI6K (ORCPT ); Mon, 24 Jun 2019 04:58:10 -0400 X-Greylist: delayed 1799 seconds by postgrey-1.27 at vger.kernel.org; Mon, 24 Jun 2019 04:58:10 EDT Received: from unknown (HELO lgemrelse6q.lge.com) (156.147.1.121) by 156.147.23.52 with ESMTP; 24 Jun 2019 17:28:09 +0900 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO localhost.localdomain) (10.177.222.33) by 156.147.1.121 with ESMTP; 24 Jun 2019 17:28:09 +0900 X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com From: Byungchul Park To: paulmck@linux.ibm.com, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, joel@joelfernandes.org, rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@lge.com Subject: [RFC] rcu: Warn that rcu ktheads cannot be spawned Date: Mon, 24 Jun 2019 17:27:32 +0900 Message-Id: <1561364852-5113-1-git-send-email-byungchul.park@lge.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? 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