Commit 067491b7 authored Dec 07, 2011 by Peter Zijlstra Committed by Ingo Molnar Dec 08, 2011

sched, nohz: Fix missing RCU read lock



Yong Zhang reported:

 > [ INFO: suspicious RCU usage. ]
 > kernel/sched/fair.c:5091 suspicious rcu_dereference_check() usage!

This is due to the sched_domain stuff being RCU protected and
commit 0b005cf5 ("sched, nohz: Implement sched group, domain
aware nohz idle load balancing") overlooking this fact.

The sd variable only lives inside the for_each_domain() block,
so we only need to wrap that.

Reported-by: Yong Zhang <yong.zhang0@gmail.com>
Tested-by: Yong Zhang <yong.zhang0@gmail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Link: http://lkml.kernel.org/r/1323264728.32012.107.camel@twins


Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent cd490c5b

kernel/sched/fair.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -5088,23 +5088,28 @@ static inline int nohz_kick_needed(struct rq *rq, int cpu)
		if (rq->nr_running >= 2)
		goto need_kick;

		rcu_read_lock();
		for_each_domain(cpu, sd) {
		struct sched_group *sg = sd->groups;
		struct sched_group_power *sgp = sg->sgp;
		int nr_busy = atomic_read(&sgp->nr_busy_cpus);

		if (sd->flags & SD_SHARE_PKG_RESOURCES && nr_busy > 1)
		goto need_kick;
		goto need_kick_unlock;

		if (sd->flags & SD_ASYM_PACKING && nr_busy != sg->group_weight
		&& (cpumask_first_and(nohz.idle_cpus_mask,
		sched_domain_span(sd)) < cpu))
		goto need_kick;
		goto need_kick_unlock;

		if (!(sd->flags & (SD_SHARE_PKG_RESOURCES \| SD_ASYM_PACKING)))
		break;
		}
		rcu_read_unlock();
		return 0;

		need_kick_unlock:
		rcu_read_unlock();
		need_kick:
		return 1;
		}

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