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 2C100C52D6C for ; Tue, 23 Aug 2022 10:37:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355687AbiHWKgy (ORCPT ); Tue, 23 Aug 2022 06:36:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38786 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354681AbiHWKV7 (ORCPT ); Tue, 23 Aug 2022 06:21:59 -0400 Received: from sin.source.kernel.org (sin.source.kernel.org [145.40.73.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 747DA2DED; Tue, 23 Aug 2022 02:03:22 -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 sin.source.kernel.org (Postfix) with ESMTPS id 97C02CE1B40; Tue, 23 Aug 2022 09:03:20 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 91142C433C1; Tue, 23 Aug 2022 09:03:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1661245399; bh=RZW52RKR3Uudu0bjrdyowQavWiTMX177M9w5TtGXDzg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=WWqKQTp89OIXzI5vkTS97YxnUbNF93d9wiqXyzAnRYPRppWFXyYRgTaqPkue1GAp4 O98PTbXFu3TJ0M202Z2IY+WPfYtgYe0Bg3jcYLxHItyNTIX+PWmFqM2HpBWsDxk6/a 4QQ2Ki64JlSOX6hi1wyLlW6oaeIcxGCJI7B1KmdQ= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Nicolas Saenz Julienne , "Peter Zijlstra (Intel)" , Valentin Schneider , Phil Auld , Sasha Levin Subject: [PATCH 4.19 065/287] nohz/full, sched/rt: Fix missed tick-reenabling bug in dequeue_task_rt() Date: Tue, 23 Aug 2022 10:23:54 +0200 Message-Id: <20220823080102.425385618@linuxfoundation.org> X-Mailer: git-send-email 2.37.2 In-Reply-To: <20220823080100.268827165@linuxfoundation.org> References: <20220823080100.268827165@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Nicolas Saenz Julienne [ Upstream commit 5c66d1b9b30f737fcef85a0b75bfe0590e16b62a ] dequeue_task_rt() only decrements 'rt_rq->rt_nr_running' after having called sched_update_tick_dependency() preventing it from re-enabling the tick on systems that no longer have pending SCHED_RT tasks but have multiple runnable SCHED_OTHER tasks: dequeue_task_rt() dequeue_rt_entity() dequeue_rt_stack() dequeue_top_rt_rq() sub_nr_running() // decrements rq->nr_running sched_update_tick_dependency() sched_can_stop_tick() // checks rq->rt.rt_nr_running, ... __dequeue_rt_entity() dec_rt_tasks() // decrements rq->rt.rt_nr_running ... Every other scheduler class performs the operation in the opposite order, and sched_update_tick_dependency() expects the values to be updated as such. So avoid the misbehaviour by inverting the order in which the above operations are performed in the RT scheduler. Fixes: 76d92ac305f2 ("sched: Migrate sched to use new tick dependency mask model") Signed-off-by: Nicolas Saenz Julienne Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Valentin Schneider Reviewed-by: Phil Auld Link: https://lore.kernel.org/r/20220628092259.330171-1-nsaenzju@redhat.com Signed-off-by: Sasha Levin --- kernel/sched/rt.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c index 70e8cd395474..9c6c3572b131 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -434,7 +434,7 @@ static inline void rt_queue_push_tasks(struct rq *rq) #endif /* CONFIG_SMP */ static void enqueue_top_rt_rq(struct rt_rq *rt_rq); -static void dequeue_top_rt_rq(struct rt_rq *rt_rq); +static void dequeue_top_rt_rq(struct rt_rq *rt_rq, unsigned int count); static inline int on_rt_rq(struct sched_rt_entity *rt_se) { @@ -516,7 +516,7 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq) rt_se = rt_rq->tg->rt_se[cpu]; if (!rt_se) { - dequeue_top_rt_rq(rt_rq); + dequeue_top_rt_rq(rt_rq, rt_rq->rt_nr_running); /* Kick cpufreq (see the comment in kernel/sched/sched.h). */ cpufreq_update_util(rq_of_rt_rq(rt_rq), 0); } @@ -602,7 +602,7 @@ static inline void sched_rt_rq_enqueue(struct rt_rq *rt_rq) static inline void sched_rt_rq_dequeue(struct rt_rq *rt_rq) { - dequeue_top_rt_rq(rt_rq); + dequeue_top_rt_rq(rt_rq, rt_rq->rt_nr_running); } static inline int rt_rq_throttled(struct rt_rq *rt_rq) @@ -1001,7 +1001,7 @@ static void update_curr_rt(struct rq *rq) } static void -dequeue_top_rt_rq(struct rt_rq *rt_rq) +dequeue_top_rt_rq(struct rt_rq *rt_rq, unsigned int count) { struct rq *rq = rq_of_rt_rq(rt_rq); @@ -1012,7 +1012,7 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq) BUG_ON(!rq->nr_running); - sub_nr_running(rq, rt_rq->rt_nr_running); + sub_nr_running(rq, count); rt_rq->rt_queued = 0; } @@ -1291,18 +1291,21 @@ static void __dequeue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flag static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int flags) { struct sched_rt_entity *back = NULL; + unsigned int rt_nr_running; for_each_sched_rt_entity(rt_se) { rt_se->back = back; back = rt_se; } - dequeue_top_rt_rq(rt_rq_of_se(back)); + rt_nr_running = rt_rq_of_se(back)->rt_nr_running; for (rt_se = back; rt_se; rt_se = rt_se->back) { if (on_rt_rq(rt_se)) __dequeue_rt_entity(rt_se, flags); } + + dequeue_top_rt_rq(rt_rq_of_se(back), rt_nr_running); } static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int flags) -- 2.35.1