Commit 383afd09 authored Mar 11, 2014 by Steven Rostedt Committed by Ingo Molnar Mar 12, 2014

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 c365c292
   "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>

parent 07082682

kernel/sched/core.c

+9 −1

Original line number	Diff line number	Diff line
		@@ -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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