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Commit b654f7de authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: Make sure to not re-read variables after validation 



We could re-read rq->rt_avg after we validated it was smaller than
total, invalidating the check and resulting in an unintended negative.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: David Rientjes <rientjes@google.com>
Link: http://lkml.kernel.org/r/1337688268.9698.29.camel@twins


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 74a5ce20

kernel/sched/fair.c

+11 −4
Original line number Diff line number Diff line
@@ -3503,15 +3503,22 @@ unsigned long __weak arch_scale_smt_power(struct sched_domain *sd, int cpu) 
unsigned long scale_rt_power(int cpu)

{

	struct rq *rq = cpu_rq(cpu);

	u64 total, available;

	u64 total, available, age_stamp, avg;



	total = sched_avg_period() + (rq->clock - rq->age_stamp);

	/*

	 * Since we're reading these variables without serialization make sure

	 * we read them once before doing sanity checks on them.

	 */

	age_stamp = ACCESS_ONCE(rq->age_stamp);

	avg = ACCESS_ONCE(rq->rt_avg);



	total = sched_avg_period() + (rq->clock - age_stamp);



	if (unlikely(total < rq->rt_avg)) {

	if (unlikely(total < avg)) {

		/* Ensures that power won't end up being negative */

		available = 0;

	} else {

		available = total - rq->rt_avg;

		available = total - avg;

	}



	if (unlikely((s64)total < SCHED_POWER_SCALE))