Commit-ID: b654f7de41b0e3903ee2b51d3b8db77fe52ce728
Gitweb: http://git.kernel.org/tip/b654f7de41b0e3903ee2b51d3b8db77fe52ce728
Author: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
AuthorDate: Tue, 22 May 2012 14:04:28 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 30 May 2012 14:02:24 +0200
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@xxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1337688268.9698.29.camel@twins
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/sched/fair.c | 15 +++++++++++----
1 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index f0380d4..2b449a7 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -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))
--
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