On Wed, 09 Apr 2014 05:50:10 +0200
Mike Galbraith <umgwanakikb...@gmail.com> 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 <umgwanakikb...@gmail.com>
> Cc: <sta...@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;
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)" <rost...@goodmis.org>
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.ca...@marge.simpson.net
Cc: sta...@vger.kernel.org
Reported-by: Mike Galbraith <umgwanakikb...@gmail.com>
Signed-off-by: Steven Rostedt <rost...@goodmis.org>
---
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
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