Commit 757dfcaa authored Nov 27, 2013 by Kirill Tkhai Committed by Ingo Molnar Dec 17, 2013

sched/rt: Fix rq's cpupri leak while enqueue/dequeue child RT entities



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@yandex.ru>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/49231385567953@web4m.yandex.ru


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 5d4cf996

kernel/sched/rt.c

+14 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}