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=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 CC405C433DB for ; Tue, 22 Dec 2020 01:38:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9493422A83 for ; Tue, 22 Dec 2020 01:38:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725924AbgLVBiV (ORCPT ); Mon, 21 Dec 2020 20:38:21 -0500 Received: from mail.kernel.org ([198.145.29.99]:51634 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725790AbgLVBiU (ORCPT ); Mon, 21 Dec 2020 20:38:20 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id CA22722A83; Tue, 22 Dec 2020 01:37:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1608601059; bh=e7GHyBCLykEq+OsooOpe6AvMkhb0yvGEjUzLLmtB5IE=; h=From:To:Cc:Subject:Date:From; b=S7TnUXef7HAgNM9UvcVjzz9/YclUeXE2EBjXHv5/T6NTyXeiBMnX6El6uTPGRz8dY dqxOvd99PntUO68BcqKlKkcx6X/Hbq1nP38mTmSRcVsj41rlZ7FUCujyZiqZUJ1KEE yHb68dgxti+G3QWfGI3IYW33oogMLTlffaO92JePCJtruNW/TGC49JVnWM/JYL65CV kh5ZOvUE6PDPzZ3c5Fmdgk56EzW5JUROpIebdKMKhlIZqi5nkhSmrLWqpNUbpQMsij MI7s2xYizsPCdpDx2Sm/pNOuujG2wJaBH9c1TelE0XNwAY2EqNHKjUJIALX0rtzkkD qcGJn6dMhOR+g== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , "Rafael J . Wysocki" , Peter Zijlstra , Ingo Molnar , Fabio Estevam , stable@vger.kernel.org, Thomas Gleixner , "Paul E . McKenney" , Len Brown , Pengutronix Kernel Team , NXP Linux Team , Daniel Lezcano , Shawn Guo , Sascha Hauer Subject: [PATCH 0/4] sched/idle: Fix missing need_resched() checks after rcu_idle_enter() Date: Tue, 22 Dec 2020 02:37:08 +0100 Message-Id: <20201222013712.15056-1-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org With Paul, we've been thinking that the idle loop wasn't twisted enough yet to deserve 2020. rcutorture, after some recent parameter changes, has been complaining about a hung task. It appears that rcu_idle_enter() may wake up a NOCB kthread but this happens after the last generic need_resched() check. Some cpuidle drivers fix it by chance but many others don't. Here is a proposed bunch of fixes. I will need to also fix the rcu_user_enter() case, likely using irq_work, since nohz_full requires irq work to support self IPI. Also more generally, this raise the question of local task wake_up() under disabled interrupts. When a wake up occurs in a preempt disabled section, it gets handled by the outer preempt_enable() call. There is no similar mechanism when a wake up occurs with interrupts disabled. I guess it is assumed to be handled, at worst, in the next tick. But a local irq work would provide instant preemption once IRQs are re-enabled. Of course this would only make sense in CONFIG_PREEMPTION, and when the tick is disabled... git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git sched/idle HEAD: f2fa6e4a070c1535b9edc9ee097167fd2b15d235 Thanks, Frederic --- Frederic Weisbecker (4): sched/idle: Fix missing need_resched() check after rcu_idle_enter() cpuidle: Fix missing need_resched() check after rcu_idle_enter() ARM: imx6q: Fix missing need_resched() check after rcu_idle_enter() ACPI: processor: Fix missing need_resched() check after rcu_idle_enter() arch/arm/mach-imx/cpuidle-imx6q.c | 7 ++++++- drivers/acpi/processor_idle.c | 10 ++++++++-- drivers/cpuidle/cpuidle.c | 33 +++++++++++++++++++++++++-------- kernel/sched/idle.c | 18 ++++++++++++------ 4 files changed, 51 insertions(+), 17 deletions(-)