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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: Peter 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2012-05-22 14:04:28 +02:00 committed by Ingo Molnar
parent 74a5ce20e6
commit b654f7de41
1 changed files with 11 additions and 4 deletions
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15
kernel/sched/fair.c
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@ -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);
if (unlikely(total < rq->rt_avg)) {
total = sched_avg_period() + (rq->clock - age_stamp);
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))