From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754785AbaDMNk2 (ORCPT ); Sun, 13 Apr 2014 09:40:28 -0400 Received: from cdptpa-outbound-snat.email.rr.com ([107.14.166.231]:41087 "EHLO cdptpa-oedge-vip.email.rr.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754492AbaDMNk0 convert rfc822-to-8bit (ORCPT ); Sun, 13 Apr 2014 09:40:26 -0400 Date: Sun, 13 Apr 2014 09:40:23 -0400 From: Steven Rostedt To: Mike Galbraith Cc: Peter Zijlstra , Ingo Molnar , LKML Subject: Re: [PATCH] sched/cpupri: fix cpupri_find() for high priority tasks Message-ID: <20140413094023.47c762fd@gandalf.local.home> In-Reply-To: <1397015410.5212.13.camel@marge.simpson.net> References: <1397015410.5212.13.camel@marge.simpson.net> X-Mailer: Claws Mail 3.9.3 (GTK+ 2.24.22; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT X-RR-Connecting-IP: 107.14.168.142:25 X-Cloudmark-Score: 0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 09 Apr 2014 05:50:10 +0200 Mike Galbraith wrote: > Hi Steven, > > Seems c92211d9b7727 introduced a buglet. > > --snip-- > > Bail on task_pri >= MAX_RT_PRIO excludes userspace prio 98 and 99 tasks, > which map to 100 and 101 respectively. > > A user reported that given two SCHED_RR tasks, one hog, one light, the light > task may be stacked on top of the hog iff prio >= 98, latency hit follows. > > Signed-off-by: Mike Galbraith > Cc: > Fixes: c92211d9b7727 sched/cpupri: Remove the vec->lock > --- > kernel/sched/cpupri.c | 3 --- > 1 file changed, 3 deletions(-) > > --- a/kernel/sched/cpupri.c > +++ b/kernel/sched/cpupri.c > @@ -70,9 +70,6 @@ int cpupri_find(struct cpupri *cp, struc > int idx = 0; > int task_pri = convert_prio(p->prio); > > - if (task_pri >= MAX_RT_PRIO) > - return 0; task_pri is used as an index into pri_to_cpu. Although I don't see how this can be called for a non RT task, the safer solution is below. -- Steve > - > for (idx = 0; idx < task_pri; idx++) { > struct cpupri_vec *vec = &cp->pri_to_cpu[idx]; > int skip = 0; > >>From 606aa467c9a51c09ce4efa320db45eee59a9bd06 Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (Red Hat)" Date: Sun, 13 Apr 2014 09:34:53 -0400 Subject: [PATCH] sched: Use CPUPRI_NR_PRIORITIES instead of MAX_RT_PRIO in cpupri check The check at the beginning of cpupri_find() makes sure that the task_pri variable does not exceed the cp->pri_to_cpu array length. But that length is CPUPRI_NR_PRIORITIES not MAX_RT_PRIO, where it will miss the last two priorities in that array. Link: http://lkml.kernel.org/r/1397015410.5212.13.camel@marge.simpson.net Cc: stable@vger.kernel.org Reported-by: Mike Galbraith Signed-off-by: Steven Rostedt --- kernel/sched/cpupri.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/cpupri.c b/kernel/sched/cpupri.c index 8b836b3..557356a 100644 --- a/kernel/sched/cpupri.c +++ b/kernel/sched/cpupri.c @@ -70,7 +70,7 @@ int cpupri_find(struct cpupri *cp, struct task_struct *p, int idx = 0; int task_pri = convert_prio(p->prio); - if (task_pri >= MAX_RT_PRIO) + if (task_pri >= CPUPRI_NR_PRIORITIES) return 0; for (idx = 0; idx < task_pri; idx++) { -- 1.8.1.4