From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758344AbbEEQuy (ORCPT ); Tue, 5 May 2015 12:50:54 -0400 Received: from smtprelay0171.hostedemail.com ([216.40.44.171]:50991 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1761114AbbEEQ3Y (ORCPT ); Tue, 5 May 2015 12:29:24 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1543:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2693:2890:2910:3138:3139:3140:3141:3142:3355:3622:3865:3866:3867:3868:3871:3872:3874:4042:4559:4605:5007:6261:7514:7875:7903:10004:10400:10848:10967:11026:11232:11473:11658:11914:12043:12198:12291:12296:12438:12517:12519:12683:12740:14096:14097:14110:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: nest20_34a51c7059e60 X-Filterd-Recvd-Size: 4230 Date: Tue, 5 May 2015 12:29:20 -0400 From: Steven Rostedt To: Thomas Gleixner Cc: Mike Galbraith , Ronny Meeus , LKML , Peter Zijlstra Subject: Re: [PATCH] sched: Handle priority boosted tasks proper in setscheduler() Message-ID: <20150505122920.7861907d@gandalf.local.home> In-Reply-To: References: X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 5 May 2015 18:08:01 +0200 (CEST) Thomas Gleixner wrote: > Reported-by: Ronny Meeus > Signed-off-by: Thomas Gleixner > --- > kernel/locking/rtmutex.c | 10 ++++++---- > kernel/sched/core.c | 11 +++++------ > 2 files changed, 11 insertions(+), 10 deletions(-) > > Index: tip/kernel/locking/rtmutex.c > =================================================================== > --- tip.orig/kernel/locking/rtmutex.c > +++ tip/kernel/locking/rtmutex.c > @@ -265,15 +265,17 @@ struct task_struct *rt_mutex_get_top_tas > } > > /* > - * Called by sched_setscheduler() to check whether the priority change > - * is overruled by a possible priority boosting. > + * Called by sched_setscheduler() to get the priority which will be > + * effective after the change. > */ > int rt_mutex_check_prio(struct task_struct *task, int newprio) > { > if (!task_has_pi_waiters(task)) > - return 0; > + return newprio; > > - return task_top_pi_waiter(task)->task->prio <= newprio; > + if (task_top_pi_waiter(task)->task->prio <= newprio) > + return task_top_pi_waiter(task)->task->prio; > + return newprio; > } > > /* > Index: tip/kernel/sched/core.c > =================================================================== > --- tip.orig/kernel/sched/core.c > +++ tip/kernel/sched/core.c > @@ -3414,7 +3414,7 @@ static int __sched_setscheduler(struct t > int newprio = dl_policy(attr->sched_policy) ? MAX_DL_PRIO - 1 : > MAX_RT_PRIO - 1 - attr->sched_priority; > int retval, oldprio, oldpolicy = -1, queued, running; > - int policy = attr->sched_policy; > + int new_effective_prio, policy = attr->sched_policy; > unsigned long flags; > const struct sched_class *prev_class; > struct rq *rq; > @@ -3596,15 +3596,14 @@ change: > oldprio = p->prio; > > /* > - * Special case for priority boosted tasks. > - * > - * If the new priority is lower or equal (user space view) > - * than the current (boosted) priority, we just store the new > + * Take priority boosted tasks into account. If the new > + * effective priority is unchanged, we just store the new > * normal parameters and do not touch the scheduler class and > * the runqueue. This will be done when the task deboost > * itself. > */ > - if (rt_mutex_check_prio(p, newprio)) { > + new_effective_prio = rt_mutex_check_prio(p, newprio); > + if (new_effective_prio == oldprio) { When I first heard of this problem, I started writing code to fix this and came up with pretty much the exact same answer. I got pulled onto other things so I never finished it, but one thing that worried me about this fix is this: T1 - FIFO policy (prio = 10) lock(rtmutex); T2 (prio = 20) lock(rtmutex) boost T1 (prio = 20) TI (prio = 20) sys_sched_setscheduler(prio = 30) TI (prio = 30) T1 (prio = 30) sys_sched_setscheduler(SCHED_OTHER) new_effective_prio = 20, oldprio = 30 Before the code stopped at the rt_mutex_check_prio(), but now it continues. Will having the policy change cause problems here? -- Steve > __setscheduler_params(p, attr); > task_rq_unlock(rq, p, &flags); > return 0;