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=-19.2 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,URIBL_BLOCKED,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 AAFBCC433E9 for ; Sat, 9 Jan 2021 02:06:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7305423AC9 for ; Sat, 9 Jan 2021 02:06:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726634AbhAICGa (ORCPT ); Fri, 8 Jan 2021 21:06:30 -0500 Received: from mail.kernel.org ([198.145.29.99]:41478 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726571AbhAICG3 (ORCPT ); Fri, 8 Jan 2021 21:06:29 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 185C023AC1; Sat, 9 Jan 2021 02:05:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1610157948; bh=DmtAyxnXnAsrifI9+yfmddVBH+zgcl5C6QweDwHY7cc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UWmX/ewLt97KeYAkf1nu+jZeVUHO/YqX78CIF8XLQakwwC1JwJ1k3U8HkTPGoXjqP EWLVeYpMQW/aFDH6uz3Q8oRKR+sKYHCYrVY3q7jC5NsSMS/t/B8dSLQmLWhq6ec0od EbERWFzb0PCS6IFxzJrcQecV8l1hcM/WXytIXrveUpctxEgo5YGLaO+sPEUg/ix8l0 +gfCkEvjew3swNFk6laFX3NdgbsBeQ7wa110m3yVTO2Va+a2GoPPwguJQgl7QnBnIA GRW5tsW8IpOphG3CBjiwtHfH/Fov2FK3AiNZGRfxzzRVFLaQZQWhxUR6VjndP9ZIGo El4sG3WD10R1Q== From: Frederic Weisbecker To: Peter Zijlstra , "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , "Rafael J . Wysocki" , Ingo Molnar , Thomas Gleixner , stable@vger.kernel.org Subject: [RFC PATCH 3/8] rcu/nocb: Perform deferred wake up before last idle's need_resched() check Date: Sat, 9 Jan 2021 03:05:31 +0100 Message-Id: <20210109020536.127953-4-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210109020536.127953-1-frederic@kernel.org> References: <20210109020536.127953-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Further debug code will help spotting the offenders. Reported-by: Paul E. McKenney Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf) Cc: stable@vger.kernel.org Cc: Rafael J. Wysocki Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Ingo Molnar Signed-off-by: Frederic Weisbecker --- include/linux/rcupdate.h | 2 ++ kernel/rcu/tree.c | 3 --- kernel/rcu/tree_plugin.h | 5 +++++ kernel/sched/idle.c | 3 +++ 4 files changed, 10 insertions(+), 3 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index de0826411311..4068234fb303 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -104,8 +104,10 @@ 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 */ /** diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index b9fff18d14d9..b6e1377774e3 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -670,10 +670,7 @@ static noinstr 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); } EXPORT_SYMBOL_GPL(rcu_idle_enter); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 7e291ce0a1d6..d5b38c28abd1 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -2187,6 +2187,11 @@ static void do_nocb_deferred_wakeup(struct rcu_data *rdp) 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; diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 305727ea0677..b601a3aa2152 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -55,6 +55,7 @@ __setup("hlt", cpu_idle_nopoll_setup); static noinline int __cpuidle cpu_idle_poll(void) { trace_cpu_idle(0, smp_processor_id()); + rcu_nocb_flush_deferred_wakeup(); stop_critical_timings(); rcu_idle_enter(); local_irq_enable(); @@ -173,6 +174,8 @@ static void cpuidle_idle_call(void) struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev); int next_state, entered_state; + rcu_nocb_flush_deferred_wakeup(); + /* * Check if the idle task must be rescheduled. If it is the * case, exit the function after re-enabling the local irq. -- 2.25.1