linux-kernel - Re: [PATCH] sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities

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Message-ID: <20131217124656.GI21999@twins.programming.kicks-ass.net>
Date:	Tue, 17 Dec 2013 13:46:56 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] sched/rt: Fix rq's cpupri leak while enqueue/dequeue
 child RT entities

On Tue, Dec 17, 2013 at 04:02:58PM +0400, Kirill Tkhai wrote:
> 
> 
> 13.12.2013, 19:42, "Peter Zijlstra" <peterz@...radead.org>:
> > On Wed, Nov 27, 2013 at 07:59:13PM +0400, Kirill Tkhai wrote:
> >
> >>  This patch touches RT group scheduling case.
> >>
> >>  Functions inc_rt_prio_smp() and dec_rt_prio_smp() change (global) rq's priority,
> >>  while rt_rq passed to them may be not the top-level rt_rq. This is wrong, because
> >>  changing of priority on a child level does not guarantee that the priority is
> >>  the highest all over the rq. So, this leak makes RT balancing unusable.
> >>
> >>  The short example: the task having the highest priority among all rq's RT tasks
> >>  (no one other task has the same priority) are waking on a throttle rt_rq.
> >>  The rq's cpupri is set to the task's priority equivalent, but real
> >>  rq->rt.highest_prio.curr is less.
> >>
> >>  The patch below fixes the problem.
> >>
> >>  It looks like all version have this bug, so I CC'ed stable mailing list.
> >
> > Yeah, I think this is right.
> >
> > cpupri stuff should indeed only be changed for the top level group.
> 
> Ingo, are you going to apply this patch? Or will you give any comments?

I queued it, Ingo should get it through me somewhere today if all things
go well.

Thanks
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