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| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2012-05-22 14:04:28 +0200 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2012-05-30 14:02:24 +0200 |
| commit | b654f7de41b0e3903ee2b51d3b8db77fe52ce728 (patch) | |
| tree | cdcd46a04d8b59d75045f1d3ae753e4843dbe2c0 /kernel | |
| parent | 74a5ce20e6eeeb3751340b390e7ac1d1d07bbf55 (diff) | |
| download | linux-b654f7de41b0e3903ee2b51d3b8db77fe52ce728.tar.gz linux-b654f7de41b0e3903ee2b51d3b8db77fe52ce728.tar.bz2 linux-b654f7de41b0e3903ee2b51d3b8db77fe52ce728.zip | |
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>
Diffstat (limited to 'kernel')
| -rw-r--r-- | 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 f0380d4987b3..2b449a762074 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)) |