From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753372AbaBLI35 (ORCPT ); Wed, 12 Feb 2014 03:29:57 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:50183 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752055AbaBLIOA (ORCPT ); Wed, 12 Feb 2014 03:14:00 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Kirill Tkhai" , "Ingo Molnar" , "Peter Zijlstra" , "Steven Rostedt" Date: Wed, 12 Feb 2014 08:10:12 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 46/79] sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities In-Reply-To: X-SA-Exim-Connect-IP: 91.84.160.45 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.55-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Kirill Tkhai commit 757dfcaa41844595964f1220f1d33182dae49976 upstream. This patch touches the RT group scheduling case. Functions inc_rt_prio_smp() and dec_rt_prio_smp() change (global) rq's priority, while rt_rq passed to them may be not the top-level rt_rq. This is wrong, because changing of priority on a child level does not guarantee that the priority is the highest all over the rq. So, this leak makes RT balancing unusable. The short example: the task having the highest priority among all rq's RT tasks (no one other task has the same priority) are waking on a throttle rt_rq. The rq's cpupri is set to the task's priority equivalent, but real rq->rt.highest_prio.curr is less. The patch below fixes the problem. Signed-off-by: Kirill Tkhai Signed-off-by: Peter Zijlstra CC: Steven Rostedt Link: http://lkml.kernel.org/r/49231385567953@web4m.yandex.ru Signed-off-by: Ingo Molnar [bwh: Backported to 3.2: adjust filename] Signed-off-by: Ben Hutchings --- kernel/sched_rt.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) --- a/kernel/sched_rt.c +++ b/kernel/sched_rt.c @@ -719,6 +719,13 @@ inc_rt_prio_smp(struct rt_rq *rt_rq, int { struct rq *rq = rq_of_rt_rq(rt_rq); +#ifdef CONFIG_RT_GROUP_SCHED + /* + * Change rq's cpupri only if rt_rq is the top queue. + */ + if (&rq->rt != rt_rq) + return; +#endif if (rq->online && prio < prev_prio) cpupri_set(&rq->rd->cpupri, rq->cpu, prio); } @@ -728,6 +735,13 @@ dec_rt_prio_smp(struct rt_rq *rt_rq, int { struct rq *rq = rq_of_rt_rq(rt_rq); +#ifdef CONFIG_RT_GROUP_SCHED + /* + * Change rq's cpupri only if rt_rq is the top queue. + */ + if (&rq->rt != rt_rq) + return; +#endif if (rq->online && rt_rq->highest_prio.curr != prev_prio) cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio.curr); }