linux-kernel - [PATCH linux-next] sched: Fix broken setscheduler()

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Date:	Wed, 5 Mar 2014 23:29:31 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH linux-next] sched: Fix broken setscheduler()

I decided to run my tests on linux-next, and my wakeup_rt tracer was
broken. After running a bisect, I found that the problem commit was:

   linux-next commit c365c292d059
   "sched: Consider pi boosting in setscheduler()"

And the reason the wake_rt tracer test was failing, was because it had
no RT task to trace. I first noticed this when running with
sched_switch event and saw that my RT task still had normal SCHED_OTHER
priority. Looking at the problem commit, I found:

 -       p->normal_prio = normal_prio(p);
 -       p->prio = rt_mutex_getprio(p);

With no

 +       p->normal_prio = normal_prio(p);
 +       p->prio = rt_mutex_getprio(p);

Reading what the commit is suppose to do, I realize that the p->prio
can't be set if the task is boosted with a higher prio, but the
p->normal_prio still needs to be set regardless, otherwise, when the
task is deboosted, it wont get the new priority.

The p->prio has to be set before "check_class_changed()" is called,
otherwise the class wont be changed.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4600bca..b1cc871 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3198,6 +3198,7 @@ static void __setscheduler_params(struct task_struct *p,
 	 * getparam()/getattr() don't report silly values for !rt tasks.
 	 */
 	p->rt_priority = attr->sched_priority;
+	p->normal_prio = normal_prio(p);
 	set_load_weight(p);
 }

@@ -3207,6 +3208,8 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
 {
 	__setscheduler_params(p, attr);

+	p->prio = rt_mutex_getprio(p);
+
 	if (dl_prio(p->prio))
 		p->sched_class = &dl_sched_class;
 	else if (rt_prio(p->prio))

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