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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 80696C433FE for ; Tue, 8 Feb 2022 16:16:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1382894AbiBHQQu (ORCPT ); Tue, 8 Feb 2022 11:16:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47690 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1382880AbiBHQQs (ORCPT ); Tue, 8 Feb 2022 11:16:48 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2A9ABC061578 for ; Tue, 8 Feb 2022 08:16:47 -0800 (PST) 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 ams.source.kernel.org (Postfix) with ESMTPS id E6497B81BDF for ; Tue, 8 Feb 2022 16:16:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 55849C340EC; Tue, 8 Feb 2022 16:16:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1644337004; bh=HiUrfd8RertoPB+w3nt8On3GrC91eaaqsyW1vNKbAKY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Su+MP0ViQpwp05yXIQ2MnQvNW5sP/evsg02ijkWOXX0w8tyEaQbWJfTaO4n7TyvEX kem1PliDn6FKMzcPF5mqUaGC2jPbVRCnQXomelxe5HsH52foVOymGL787wNbS3BRnG qCgSEkClF+6lBxR025Jx7wOzVeAK/QPG8bTCKDnQYQ6bAgQN8RVPplfabODO4T1LFp 2g2w2HVd31kg+dTA9baOoAMkioxD1V39aEdhHVCPVs3PcEffrjsvguy6ssbc50DUUD cIMXgf1v888WfaWwQfI5bgsq5SSj6WlwTt8hKSzFOFryJQOKnJaDImAu+dmVP8J60Z vjSqwRXEK+zYg== From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , "Paul E . McKenney" , Peter Zijlstra , Thomas Gleixner , Paul Menzel Subject: [PATCH 2/3] tick/rcu: Stop allowing RCU_SOFTIRQ in idle Date: Tue, 8 Feb 2022 17:16:34 +0100 Message-Id: <20220208161635.544701-3-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20220208161635.544701-1-frederic@kernel.org> References: <20220208161635.544701-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org RCU_SOFTIRQ used to be special in that it could be raised on purpose within the idle path to prevent from stopping the tick. Some code still prevents from unnecessary warnings related to this specific behaviour while entering in dynticks-idle mode. However the nohz layout has changed quite a bit in ten years, and the removal of CONFIG_RCU_FAST_NO_HZ has been the final straw to this safe-conduct. Now the RCU_SOFTIRQ vector is expected to be raised from sane places. A remaining corner case is admitted though when the vector is invoked in fragile hotplug path. Signed-off-by: Frederic Weisbecker Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Paul E. McKenney Cc: Paul Menzel --- include/linux/interrupt.h | 8 ++++++- kernel/time/tick-sched.c | 50 +++++++++++++++++++++++++++++++-------- 2 files changed, 47 insertions(+), 11 deletions(-) diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h index 9367f1cb2e3c..9613326d2f8a 100644 --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -579,7 +579,13 @@ enum NR_SOFTIRQS }; -#define SOFTIRQ_STOP_IDLE_MASK (~(1 << RCU_SOFTIRQ)) +/* + * Ignoring the RCU vector after ksoftirqd is parked is fine + * because: + * 1) rcutree_migrate_callbacks() takes care of the queue. + * 2) rcu_report_dead() reports the final quiescent states. + */ +#define SOFTIRQ_HOTPLUG_SAFE_MASK (BIT(RCU_SOFTIRQ)) /* map softirq index to softirq name. update 'softirq_to_name' in * kernel/softirq.c when adding a new softirq. diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 2abb5112feb9..1e923f307f06 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -982,6 +982,45 @@ static void tick_nohz_full_update_tick(struct tick_sched *ts) __tick_nohz_full_update_tick(ts, ktime_get()); } +/* + * A pending softirq outside an IRQ (or softirq disabled section) context + * should be waiting for ksoftirqd to handle it. Therefore we shouldn't + * reach here due to the need_resched() early check in can_stop_idle_tick(). + * + * However if we are between CPUHP_AP_SMPBOOT_THREADS and CPU_TEARDOWN_CPU on the + * cpu_down() process, softirqs can still be raised while ksoftirqd is parked, + * triggering the below since wakep_softirqd() is ignored. + * + */ +static bool report_idle_softirq(void) +{ + static int ratelimit; + unsigned int pending = local_softirq_pending(); + + if (likely(!pending)) + return false; + + /* Some softirqs claim to be safe against hotplug and ksoftirqd parking */ + if (!cpu_active(smp_processor_id())) { + pending &= ~SOFTIRQ_HOTPLUG_SAFE_MASK; + if (!pending) + return false; + } + + if (ratelimit < 10) + return false; + + /* On RT, softirqs handling may be waiting on some lock */ + if (!local_bh_blocked()) + return false; + + pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n", + pending); + ratelimit++; + + return true; +} + static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) { /* @@ -1008,17 +1047,8 @@ static bool can_stop_idle_tick(int cpu, struct tick_sched *ts) if (need_resched()) return false; - if (unlikely(local_softirq_pending())) { - static int ratelimit; - - if (ratelimit < 10 && !local_bh_blocked() && - (local_softirq_pending() & SOFTIRQ_STOP_IDLE_MASK)) { - pr_warn("NOHZ tick-stop error: Non-RCU local softirq work is pending, handler #%02x!!!\n", - (unsigned int) local_softirq_pending()); - ratelimit++; - } + if (unlikely(report_idle_softirq())) return false; - } if (tick_nohz_full_enabled()) { /* -- 2.25.1