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=-19.3 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 D50FDC433E0 for ; Wed, 6 Jan 2021 16:53:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A4F6B216C4 for ; Wed, 6 Jan 2021 16:53:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727624AbhAFQxP (ORCPT ); Wed, 6 Jan 2021 11:53:15 -0500 Received: from mail.kernel.org ([198.145.29.99]:55798 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727271AbhAFQxO (ORCPT ); Wed, 6 Jan 2021 11:53:14 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id E036623331; Wed, 6 Jan 2021 16:52:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1609951954; bh=R0SAKfueyJltvmZA7TSOV4iN4gDsf3a43uV6vHVaTSU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=M2DtfzXDssSqGNTB2emk//OWUOA0wGtBqnW2QW5acrfMgQTrhJFPUtIpSvSgng9AT 14pZfHQvbVSMxQljxIvEUem4ymZJEGM0pw71YxEfB/yD1mI2+QxA2f/M2I1tueoPLv upI7wPbE6JbJgVL5Vhq+aBwDgbBXdm8wKFo00AhD2OjXGNqDGgs4wlAs6p1l/kdbof oNXJohOPbhXFyep/O59ux/6oYd61uyEP7NBalMJWR4S5U10b7Yxp1K5P0Y7RMNG4c/ LxVD5Mmxv0TKRMZlIEVSo4KAUqd3hAnxKVsSSmTUZWMgzYHwvhkLfuEw76PGrdQTji +jkd4sewsMObg== From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 3/4] rcu: Do not NMI offline CPUs Date: Wed, 6 Jan 2021 08:52:30 -0800 Message-Id: <20210106165231.20441-3-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20210106165210.GA20296@paulmck-ThinkPad-P72> References: <20210106165210.GA20296@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Currently, RCU CPU stall warning messages will NMI whatever CPU looks like it is blocking either the current grace period or the grace-period kthread. This can produce confusing output if the target CPU is offline. This commit therefore checks for offline CPUs. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_stall.h | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 35c1355..29cf096 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -333,9 +333,12 @@ static void rcu_dump_cpu_stacks(void) rcu_for_each_leaf_node(rnp) { raw_spin_lock_irqsave_rcu_node(rnp, flags); for_each_leaf_node_possible_cpu(rnp, cpu) - if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) - if (!trigger_single_cpu_backtrace(cpu)) + if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { + if (cpu_is_offline(cpu)) + pr_err("Offline CPU %d blocking current GP.\n", cpu); + else if (!trigger_single_cpu_backtrace(cpu)) dump_cpu_task(cpu); + } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } } @@ -466,9 +469,13 @@ static void rcu_check_gp_kthread_starvation(void) pr_err("RCU grace-period kthread stack dump:\n"); sched_show_task(gpk); if (cpu >= 0) { - pr_err("Stack dump where RCU grace-period kthread last ran:\n"); - if (!trigger_single_cpu_backtrace(cpu)) - dump_cpu_task(cpu); + if (cpu_is_offline(cpu)) { + pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); + } else { + pr_err("Stack dump where RCU GP kthread last ran:\n"); + if (!trigger_single_cpu_backtrace(cpu)) + dump_cpu_task(cpu); + } } wake_up_process(gpk); } -- 2.9.5