[PATCHv2 6/7] sched: Wrap rq->rd->overload accesses with READ/WRITE_ONCE

From: Morten Rasmussen
Date: Thu Mar 15 2018 - 10:47:44 EST


From: Valentin Schneider <valentin.schneider@xxxxxxx>

This variable can be read and set locklessly within update_sd_lb_stats().
As such, READ/WRITE_ONCE are added to make sure nothing terribly wrong
can happen because of the compiler.

cc: Ingo Molnar <mingo@xxxxxxxxxx>
cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
Signed-off-by: Morten Rasmussen <morten.rasmussen@xxxxxxx>
---
kernel/sched/fair.c | 6 +++---
kernel/sched/sched.h | 4 ++--
2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index fe4824a37302..4e79ec8760be 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8220,8 +8220,8 @@ static inline void update_sd_lb_stats(struct lb_env *env, struct sd_lb_stats *sd

if (!env->sd->parent) {
/* update overload indicator if we are at root domain */
- if (env->dst_rq->rd->overload != overload)
- env->dst_rq->rd->overload = overload;
+ if (READ_ONCE(env->dst_rq->rd->overload) != overload)
+ WRITE_ONCE(env->dst_rq->rd->overload, overload);
}
}

@@ -9659,7 +9659,7 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
rq_unpin_lock(this_rq, rf);

if (this_rq->avg_idle < sysctl_sched_migration_cost ||
- !this_rq->rd->overload) {
+ !READ_ONCE(this_rq->rd->overload)) {

rcu_read_lock();
sd = rcu_dereference_check_sched_domain(this_rq->sd);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 5379f647016d..31847b7f7d47 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1651,8 +1651,8 @@ static inline void add_nr_running(struct rq *rq, unsigned count)

if (prev_nr < 2 && rq->nr_running >= 2) {
#ifdef CONFIG_SMP
- if (!rq->rd->overload)
- rq->rd->overload = 1;
+ if (!READ_ONCE(rq->rd->overload))
+ WRITE_ONCE(rq->rd->overload, 1);
#endif
}

--
2.7.4