From nobody Tue Apr 28 11:04:37 2026 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 C8137C43334 for ; Tue, 28 Jun 2022 09:23:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344175AbiF1JX0 (ORCPT ); Tue, 28 Jun 2022 05:23:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48198 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344152AbiF1JXS (ORCPT ); Tue, 28 Jun 2022 05:23:18 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 4667E1EECA for ; Tue, 28 Jun 2022 02:23:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1656408193; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=ZQ8PbVRfKtLH2BnQKm5WBZD6aRMJWU7raZsWJy2qDfc=; b=bxyIDItE7zdLWCgiVdyKIgEs5TAypVyRHXkS3w0XY00SNXVaEsAvh21z11s9Oml8J6aFsw zIdG+XmE6sp7VzvpDyQsDndrRC6JAUKnBTisSQouBv/nvxSX3Rmt/sDTU+Ddz/oMvE4upC s5nsZYmoUCw0opBjXuzgNrvkMaOGGVs= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-319-9p2IRh4zPbCDIYpVyLlwWQ-1; Tue, 28 Jun 2022 05:23:10 -0400 X-MC-Unique: 9p2IRh4zPbCDIYpVyLlwWQ-1 Received: by mail-wm1-f72.google.com with SMTP id v125-20020a1cac83000000b0039c832fbd02so8602976wme.4 for ; Tue, 28 Jun 2022 02:23:10 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=ZQ8PbVRfKtLH2BnQKm5WBZD6aRMJWU7raZsWJy2qDfc=; b=64NMiqqXfVorAWYXDI6gEbY8DUZG+1UMsYXXtj3ccXQLqRF5IkAO4Xb8NIdWhZAe2q 4guUuKAe/NkPv5KExWksPXNa9vIJ4n3UMdJw3+d689ft00DOuuoxtKLzu3lDQUAN+YZL XW/Vv8soj6/kWrAA2SksDwpbW3O+aShiNXCjPS1+hrWRlj1VQVDl3ZBTlYtlF+y/b5B+ zTNfIb5DJaMH1w+bk1gNi/eUg6Zo5BlpGhWi6ZLu9IknddAIBSQsrqb3aGyWCjNNZ6yz zFIS25WMwjUp7ipLMoehGPmoPoBfk/W02n1AK+LjeI3MUWYDhIEaSYyHwZ/00kOk6lxG 7ogw== X-Gm-Message-State: AJIora+QAWLGw0dja2NNrBKnTYGg72VmjwP4gYG5U9RsaY7XpsoAwXIe oZUdM5LIaz160y9+E7qArHurHPoTrMZasTNnRutQBg8C7uNbegNcoV8QCaYn4F5Ms5hGggDHv96 SARd/F6eZAw6adrFxIrGys3Or4SNG9Jmp8qpbDeyS9R8oBAD137cgaMKyLL2CdQv99Z9oGwHHDh UJ X-Received: by 2002:adf:e68b:0:b0:21d:1c8d:9891 with SMTP id r11-20020adfe68b000000b0021d1c8d9891mr2922152wrm.37.1656408189370; Tue, 28 Jun 2022 02:23:09 -0700 (PDT) X-Google-Smtp-Source: AGRyM1srDW/+3lydTME/MMivmI4UhbCnrKvSp+Uias0Oz8IX8uy8HiHJgBlQ1o4KdvkvMPijOCyTHA== X-Received: by 2002:adf:e68b:0:b0:21d:1c8d:9891 with SMTP id r11-20020adfe68b000000b0021d1c8d9891mr2922119wrm.37.1656408189104; Tue, 28 Jun 2022 02:23:09 -0700 (PDT) Received: from vian.redhat.com ([2a0c:5a80:1b12:b300:47b0:25ba:1a2e:72ac]) by smtp.gmail.com with ESMTPSA id v14-20020a05600c214e00b0039c96b97359sm10021630wml.37.2022.06.28.02.23.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Jun 2022 02:23:08 -0700 (PDT) From: Nicolas Saenz Julienne To: linux-kernel@vger.kernel.org, fweisbec@gmail.com Cc: bristot@redhat.com, vschneid@redhat.com, cmetcalf@ezchip.com, mgorman@suse.de, bsegall@google.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, vincent.guittot@linaro.org, juri.lelli@redhat.com, peterz@infradead.org, mingo@redhat.com, mtosatti@redhat.com, Nicolas Saenz Julienne Subject: [PATCH] nohz/full, sched/rt: Fix missed tick-reenabling bug in dequeue_task_rt Date: Tue, 28 Jun 2022 11:22:59 +0200 Message-Id: <20220628092259.330171-1-nsaenzju@redhat.com> X-Mailer: git-send-email 2.36.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" 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 Reviewed-by: Phil Auld Reviewed-by: Valentin Schneider --- 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 8c9ed96648409..55f39c8f42032 100644 --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -480,7 +480,7 @@ static inline void rt_queue_push_tasks(struct rq *rq) #endif /* CONFIG_SMP */ =20 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); =20 static inline int on_rt_rq(struct sched_rt_entity *rt_se) { @@ -601,7 +601,7 @@ static void sched_rt_rq_dequeue(struct rt_rq *rt_rq) rt_se =3D rt_rq->tg->rt_se[cpu]; =20 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); } @@ -687,7 +687,7 @@ static inline void sched_rt_rq_enqueue(struct rt_rq *rt= _rq) =20 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); } =20 static inline int rt_rq_throttled(struct rt_rq *rt_rq) @@ -1089,7 +1089,7 @@ static void update_curr_rt(struct rq *rq) } =20 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 =3D rq_of_rt_rq(rt_rq); =20 @@ -1100,7 +1100,7 @@ dequeue_top_rt_rq(struct rt_rq *rt_rq) =20 BUG_ON(!rq->nr_running); =20 - sub_nr_running(rq, rt_rq->rt_nr_running); + sub_nr_running(rq, count); rt_rq->rt_queued =3D 0; =20 } @@ -1486,18 +1486,21 @@ static void __dequeue_rt_entity(struct sched_rt_ent= ity *rt_se, unsigned int flag static void dequeue_rt_stack(struct sched_rt_entity *rt_se, unsigned int f= lags) { struct sched_rt_entity *back =3D NULL; + unsigned int rt_nr_running; =20 for_each_sched_rt_entity(rt_se) { rt_se->back =3D back; back =3D rt_se; } =20 - dequeue_top_rt_rq(rt_rq_of_se(back)); + rt_nr_running =3D rt_rq_of_se(back)->rt_nr_running; =20 for (rt_se =3D back; rt_se; rt_se =3D 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); } =20 static void enqueue_rt_entity(struct sched_rt_entity *rt_se, unsigned int = flags) --=20 2.36.1