This is a note to let you know that I've just added the patch titled
sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-rt-fix-rq-s-cpupri-leak-while-enqueue-dequeue-child-rt-entities.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 757dfcaa41844595964f1220f1d33182dae49976 Mon Sep 17 00:00:00 2001
From: Kirill Tkhai <tkhai@xxxxxxxxx>
Date: Wed, 27 Nov 2013 19:59:13 +0400
Subject: sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities
From: Kirill Tkhai <tkhai@xxxxxxxxx>
commit 757dfcaa41844595964f1220f1d33182dae49976 upstream.
This patch touches the 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.
Signed-off-by: Kirill Tkhai <tkhai@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
Link: http://lkml.kernel.org/r/49231385567953@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/rt.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -899,6 +899,13 @@ inc_rt_prio_smp(struct rt_rq *rt_rq, int
{
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);
}
@@ -908,6 +915,13 @@ dec_rt_prio_smp(struct rt_rq *rt_rq, int
{
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);
}
Patches currently in stable-queue which might be from tkhai@xxxxxxxxx are
queue-3.12/sched-rt-fix-rq-s-cpupri-leak-while-enqueue-dequeue-child-rt-entities.patch
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