Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933289AbdC3KNe (ORCPT ); Thu, 30 Mar 2017 06:13:34 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:54718 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932839AbdC3KNb (ORCPT ); Thu, 30 Mar 2017 06:13:31 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Peter Zijlstra , Sebastian Andrzej Siewior , Linus Torvalds , Mike Galbraith , Thomas Gleixner , Ingo Molnar Subject: [PATCH 4.10 16/17] sched/rt: Add a missing rescheduling point Date: Thu, 30 Mar 2017 12:00:31 +0200 Message-Id: <20170330095928.198557602@linuxfoundation.org> X-Mailer: git-send-email 2.12.1 In-Reply-To: <20170330095925.918515862@linuxfoundation.org> References: <20170330095925.918515862@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2617 Lines: 76 4.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Andrzej Siewior commit 619bd4a71874a8fd78eb6ccf9f272c5e98bcc7b7 upstream. Since the change in commit: fd7a4bed1835 ("sched, rt: Convert switched_{from, to}_rt() / prio_changed_rt() to balance callbacks") ... we don't reschedule a task under certain circumstances: Lets say task-A, SCHED_OTHER, is running on CPU0 (and it may run only on CPU0) and holds a PI lock. This task is removed from the CPU because it used up its time slice and another SCHED_OTHER task is running. Task-B on CPU1 runs at RT priority and asks for the lock owned by task-A. This results in a priority boost for task-A. Task-B goes to sleep until the lock has been made available. Task-A is already runnable (but not active), so it receives no wake up. The reality now is that task-A gets on the CPU once the scheduler decides to remove the current task despite the fact that a high priority task is enqueued and waiting. This may take a long time. The desired behaviour is that CPU0 immediately reschedules after the priority boost which made task-A the task with the lowest priority. Suggested-by: Peter Zijlstra Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Cc: Linus Torvalds Cc: Mike Galbraith Cc: Thomas Gleixner Fixes: fd7a4bed1835 ("sched, rt: Convert switched_{from, to}_rt() prio_changed_rt() to balance callbacks") Link: http://lkml.kernel.org/r/20170124144006.29821-1-bigeasy@linutronix.de Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- kernel/sched/deadline.c | 3 +-- kernel/sched/rt.c | 3 +-- 2 files changed, 2 insertions(+), 4 deletions(-) --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1729,12 +1729,11 @@ static void switched_to_dl(struct rq *rq #ifdef CONFIG_SMP if (tsk_nr_cpus_allowed(p) > 1 && rq->dl.overloaded) queue_push_tasks(rq); -#else +#endif if (dl_task(rq->curr)) check_preempt_curr_dl(rq, p, 0); else resched_curr(rq); -#endif } } --- a/kernel/sched/rt.c +++ b/kernel/sched/rt.c @@ -2198,10 +2198,9 @@ static void switched_to_rt(struct rq *rq #ifdef CONFIG_SMP if (tsk_nr_cpus_allowed(p) > 1 && rq->rt.overloaded) queue_push_tasks(rq); -#else +#endif /* CONFIG_SMP */ if (p->prio < rq->curr->prio) resched_curr(rq); -#endif /* CONFIG_SMP */ } }