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=-18.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham 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 94746C433DB for ; Mon, 1 Mar 2021 17:57:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6260C65391 for ; Mon, 1 Mar 2021 17:57:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238665AbhCAR5Z (ORCPT ); Mon, 1 Mar 2021 12:57:25 -0500 Received: from mail.kernel.org ([198.145.29.99]:46586 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238549AbhCARvs (ORCPT ); Mon, 1 Mar 2021 12:51:48 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 001B064FDF; Mon, 1 Mar 2021 17:00:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1614618050; bh=DTHB7zNqj5E+xXfn7TmsMUOtjvT7RHZAV54sKePRIS0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=07oxLyb1TC6hm77O/L/iItj9QeDg0n2/u8OreTKtp499HA2rhzv0ShajwVWY15vrF 6h92YgKwrGy8m8pgBHWQ0V9vZvnEAdSNcYJoXJL3HumV6mCXaWyvzotAofPjeuuP6U 0w2a1i+yNCb2XTpEPOfGXo7szDivEF7otPoHrZq8= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Paul E. McKenney" , Frederic Weisbecker , "Peter Zijlstra (Intel)" , Ingo Molnar Subject: [PATCH 5.4 288/340] rcu/nocb: Perform deferred wake up before last idles need_resched() check Date: Mon, 1 Mar 2021 17:13:52 +0100 Message-Id: <20210301161102.461403082@linuxfoundation.org> X-Mailer: git-send-email 2.30.1 In-Reply-To: <20210301161048.294656001@linuxfoundation.org> References: <20210301161048.294656001@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Frederic Weisbecker commit 43789ef3f7d61aa7bed0cb2764e588fc990c30ef upstream. Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP kthread (rcuog) to be serviced. Usually a local wake up happening while running the idle task is handled in one of the need_resched() checks carefully placed within the idle loop that can break to the scheduler. Unfortunately the call to rcu_idle_enter() is already beyond the last generic need_resched() check and we may halt the CPU with a resched request unhandled, leaving the task hanging. Fix this with splitting the rcuog wakeup handling from rcu_idle_enter() and place it before the last generic need_resched() check in the idle loop. It is then assumed that no call to call_rcu() will be performed after that in the idle loop until the CPU is put in low power mode. Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf) Reported-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-3-frederic@kernel.org Signed-off-by: Greg Kroah-Hartman --- include/linux/rcupdate.h | 2 ++ kernel/rcu/tree.c | 3 --- kernel/rcu/tree_plugin.h | 5 +++++ kernel/sched/idle.c | 1 + 4 files changed, 8 insertions(+), 3 deletions(-) --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -96,8 +96,10 @@ static inline void rcu_user_exit(void) { #ifdef CONFIG_RCU_NOCB_CPU void rcu_init_nohz(void); +void rcu_nocb_flush_deferred_wakeup(void); #else /* #ifdef CONFIG_RCU_NOCB_CPU */ static inline void rcu_init_nohz(void) { } +static inline void rcu_nocb_flush_deferred_wakeup(void) { } #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ /** --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -599,10 +599,7 @@ static void rcu_eqs_enter(bool user) */ void rcu_idle_enter(void) { - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - lockdep_assert_irqs_disabled(); - do_nocb_deferred_wakeup(rdp); rcu_eqs_enter(false); } --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2190,6 +2190,11 @@ static void do_nocb_deferred_wakeup(stru do_nocb_deferred_wakeup_common(rdp); } +void rcu_nocb_flush_deferred_wakeup(void) +{ + do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data)); +} + void __init rcu_init_nohz(void) { int cpu; --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -249,6 +249,7 @@ static void do_idle(void) } arch_cpu_idle_enter(); + rcu_nocb_flush_deferred_wakeup(); /* * In poll mode we reenable interrupts and spin. Also if we