sched/fair: Wrap rq->rd->overload accesses with READ/WRITE_ONCE()

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.

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Cc: gaku.inami.xh@renesas.com
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1530699470-29808-9-git-send-email-morten.rasmussen@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 5 insertions, 5 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 23017939ecab..d9c4e97bfebd 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8058,8 +8058,8 @@ next_group:
 
         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);
         }
 }
 
@@ -9502,7 +9502,7 @@ 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 4d181478c5b8..938063639793 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1697,8 +1697,8 @@ 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
         }