linux-kernel - Re: [PATCH v3] sched: Fix broken setscheduler()

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Date:	Wed, 12 Mar 2014 11:41:24 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Steven Rostedt <rostedt@...dmis.org>
cc:	Juri Lelli <juri.lelli@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v3] sched: Fix broken setscheduler()

On Tue, 11 Mar 2014, Steven Rostedt wrote:

> 
> 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.
> 
> Link: http://lkml.kernel.org/r/20140306120438.638bfe94@gandalf.local.home
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>

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