From nobody Tue Apr 7 05:38:09 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EAD08ECAAD3 for ; Wed, 31 Aug 2022 18:08:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232367AbiHaSIa (ORCPT ); Wed, 31 Aug 2022 14:08:30 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42938 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230249AbiHaSIL (ORCPT ); Wed, 31 Aug 2022 14:08:11 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1616E3426; Wed, 31 Aug 2022 11:08:08 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 6EA4D61BFB; Wed, 31 Aug 2022 18:08:08 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 92A4FC43147; Wed, 31 Aug 2022 18:08:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1661969287; bh=/uL5W9eLHl+SeaTGYxjhOKKa+37RcoDRIc6rSK6aGYY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ya7lrUH6BuPPFoMDt5cTFT8U63Rj19ssY0sIun5dQA7NevNz8LavQbqDHbSFtqfk3 RWbx1nPgIdMjxpfJuT5T1x6xNQFl9NtkJtKfdYgR1WZz6zbeYDBIq+9ZFzM77f/J6b vZ7iWq0FuBAh2NcunU4Hv2KLHTQdwli0b2VVdeMl0+zgUygvNZ0dgDe/m6KVTDJgNV IXq+p21r1Ww/B6U3q47VemMbwYWCwYNALdUgUP5b/zNeu3dpugBJrKqTRD85AncDmt fziOsWN4xSNi0kwUTiIk9tNZbNzlUzRBoBXhTnqHtDEusZHSOHt6RwuaB8CWP/ksf4 xiKWAZqiHP5aQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 022C75C0950; Wed, 31 Aug 2022 11:08:07 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, Zhen Lei , "Paul E . McKenney" , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider Subject: [PATCH rcu 07/10] sched/debug: Try trigger_single_cpu_backtrace(cpu) in dump_cpu_task() Date: Wed, 31 Aug 2022 11:08:02 -0700 Message-Id: <20220831180805.2693546-7-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20220831180759.GA2693289@paulmck-ThinkPad-P17-Gen-1> References: <20220831180759.GA2693289@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Zhen Lei The trigger_all_cpu_backtrace() function attempts to send an NMI to the target CPU, which usually provides much better stack traces than the dump_cpu_task() function's approach of dumping that stack from some other CPU. So much so that most calls to dump_cpu_task() only happen after a call to trigger_all_cpu_backtrace() has failed. And the exception to this rule really should attempt to use trigger_all_cpu_backtrace() first. Therefore, move the trigger_all_cpu_backtrace() invocation into dump_cpu_task(). Signed-off-by: Zhen Lei Signed-off-by: Paul E. McKenney Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Ben Segall Cc: Mel Gorman Cc: Daniel Bristot de Oliveira Cc: Valentin Schneider --- kernel/rcu/tree_stall.h | 5 ++--- kernel/sched/core.c | 3 +++ kernel/smp.c | 3 +-- 3 files changed, 6 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index c3fbbcc09327f..5653560573e22 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -368,7 +368,7 @@ static void rcu_dump_cpu_stacks(void) 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)) + else dump_cpu_task(cpu); } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); @@ -511,8 +511,7 @@ static void rcu_check_gp_kthread_starvation(void) 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); + dump_cpu_task(cpu); } } wake_up_process(gpk); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ee28253c9ac0c..e15b6a7f34f47 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -11183,6 +11183,9 @@ struct cgroup_subsys cpu_cgrp_subsys =3D { =20 void dump_cpu_task(int cpu) { + if (trigger_single_cpu_backtrace(cpu)) + return; + pr_info("Task dump for CPU %d:\n", cpu); sched_show_task(cpu_curr(cpu)); } diff --git a/kernel/smp.c b/kernel/smp.c index 650810a6f29b3..e8cdc025a046f 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -370,8 +370,7 @@ static bool csd_lock_wait_toolong(struct __call_single_= data *csd, u64 ts0, u64 * if (cpu >=3D 0) { if (static_branch_unlikely(&csdlock_debug_extended)) csd_lock_print_extended(csd, cpu); - if (!trigger_single_cpu_backtrace(cpu)) - dump_cpu_task(cpu); + dump_cpu_task(cpu); if (!cpu_cur_csd) { pr_alert("csd: Re-sending CSD lock (#%d) IPI from CPU#%02d to CPU#%02d\= n", *bug_id, raw_smp_processor_id(), cpu); arch_send_call_function_single_ipi(cpu); --=20 2.31.1.189.g2e36527f23