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

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Date:	Thu, 12 Dec 2013 14:30:03 +0400
From:	Kirill Tkhai <tkhai@...dex.ru>
To:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.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

Ping!

27.11.2013, 19:59, "Kirill Tkhai" <tkhai@...dex.ru>:
> 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.
>
> Signed-off-by: Kirill Tkhai <tkhai@...dex.ru>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Peter Zijlstra <peterz@...radead.org>
> CC: Steven Rostedt <rostedt@...dmis.org>
> CC: stable@...r.kernel.org
>---
> kernel/sched/rt.c |   14 ++++++++++++++
> 1 files changed, 14 insertions(+), 0 deletions(-)
>diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
>index 7d57275..1c40655 100644
>--- a/kernel/sched/rt.c
>+++ b/kernel/sched/rt.c
>@@ -901,6 +901,13 @@ inc_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
> {
> 	struct rq *rq = rq_of_rt_rq(rt_rq);
> 
>+#ifdef CONFIG_RT_GROUP_SCHED
>+	/*
>+	 * Change rq's cpupri only if rt_rq is the top queue.
>+	 */
>+	if (&rq->rt != rt_rq)
>+		return;
>+#endif
> 	if (rq->online && prio < prev_prio)
> 		cpupri_set(&rq->rd->cpupri, rq->cpu, prio);
> }
>@@ -910,6 +917,13 @@ dec_rt_prio_smp(struct rt_rq *rt_rq, int prio, int prev_prio)
> {
> 	struct rq *rq = rq_of_rt_rq(rt_rq);
> 
>+#ifdef CONFIG_RT_GROUP_SCHED
>+	/*
>+	 * Change rq's cpupri only if rt_rq is the top queue.
>+	 */
>+	if (&rq->rt != rt_rq)
>+		return;
>+#endif
> 	if (rq->online && rt_rq->highest_prio.curr != prev_prio)
> 		cpupri_set(&rq->rd->cpupri, rq->cpu, rt_rq->highest_prio.curr);
> }
--
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