linux-kernel - [tip:sched/core] sched: Fix broken setscheduler()

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Message-ID: <tip-383afd0971538b3d77532a56404b24cfe967b5dd@git.kernel.org>
Date:	Wed, 12 Mar 2014 03:10:19 -0700
From:	tip-bot for Steven Rostedt <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	peterz@...radead.org, rostedt@...dmis.org, tglx@...utronix.de,
	bigeasy@...utronix.de, juri.lelli@...il.com
Subject: [tip:sched/core] sched: Fix broken setscheduler()

Commit-ID:  383afd0971538b3d77532a56404b24cfe967b5dd
Gitweb:     http://git.kernel.org/tip/383afd0971538b3d77532a56404b24cfe967b5dd
Author:     Steven Rostedt <rostedt@...dmis.org>
AuthorDate: Tue, 11 Mar 2014 19:24:20 -0400
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 12 Mar 2014 10:48:59 +0100

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.

Also added fix to newprio to include a check for deadline policy that
was missing. This change was suggested by Juri Lelli.

Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
Cc: SebastianAndrzej Siewior <bigeasy@...utronix.de>
Cc: Juri Lelli <juri.lelli@...il.com>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Link: http://lkml.kernel.org/r/20140306120438.638bfe94@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/core.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9e126a2..ae365aa 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3195,6 +3195,7 @@ 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);
 }
 
@@ -3204,6 +3205,12 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
 {
 	__setscheduler_params(p, attr);
 
+	/*
+	 * If we get here, there was no pi waiters boosting the
+	 * task. It is safe to use the normal prio.
+	 */
+	p->prio = normal_prio(p);
+
 	if (dl_prio(p->prio))
 		p->sched_class = &dl_sched_class;
 	else if (rt_prio(p->prio))
@@ -3262,7 +3269,8 @@ static int __sched_setscheduler(struct task_struct *p,
 				const struct sched_attr *attr,
 				bool user)
 {
-	int newprio = MAX_RT_PRIO - 1 - attr->sched_priority;
+	int newprio = dl_policy(attr->sched_policy) ? MAX_DL_PRIO - 1 :
+		      MAX_RT_PRIO - 1 - attr->sched_priority;
 	int retval, oldprio, oldpolicy = -1, on_rq, running;
 	int policy = attr->sched_policy;
 	unsigned long flags;
--
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