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List:       linux-kernel
Subject:    [PATCH] sched/cpupri: fix cpupri_find() for high priority tasks
From:       Mike Galbraith <umgwanakikbuti () gmail ! com>
Date:       2014-04-09 3:50:10
Message-ID: 1397015410.5212.13.camel () marge ! simpson ! net
[Download message 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;


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