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From: Mike Galbraith <umgwanakikbuti@gmail.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH] sched/cpupri: fix cpupri_find() for high priority tasks
Date: Wed, 09 Apr 2014 05:50:10 +0200
Message-ID: <1397015410.5212.13.camel@marge.simpson.net> (raw)

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 <umgwanakikbuti@gmail.com>
Cc: <stable@vger.kernel.org>
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;
-
 	for (idx = 0; idx < task_pri; idx++) {
 		struct cpupri_vec *vec  = &cp->pri_to_cpu[idx];
 		int skip = 0;



             reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-09  3:50 Mike Galbraith [this message]
2014-04-13 13:40 ` Steven Rostedt
2014-04-13 13:48   ` Steven Rostedt
2014-05-08 10:41 ` [tip:sched/core] sched: Use CPUPRI_NR_PRIORITIES instead of MAX_RT_PRIO in cpupri check tip-bot for Steven Rostedt (Red Hat)

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