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Subject[tip:sched/core] sched: Fix broken setscheduler()
Commit-ID:  383afd0971538b3d77532a56404b24cfe967b5dd
Gitweb: http://git.kernel.org/tip/383afd0971538b3d77532a56404b24cfe967b5dd
Author: Steven Rostedt <rostedt@goodmis.org>
AuthorDate: Tue, 11 Mar 2014 19:24:20 -0400
Committer: Ingo Molnar <mingo@kernel.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@goodmis.org>
Cc: SebastianAndrzej Siewior <bigeasy@linutronix.de>
Cc: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20140306120438.638bfe94@gandalf.local.home
Signed-off-by: Ingo Molnar <mingo@kernel.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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