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

[tip-bot for Valentin Schneider <tipbot@zytor.com>]

Commit-ID:  e90c8fe15a3bf93a23088bcf1a56a0fa391d4e50
Gitweb:     https://git.kernel.org/tip/e90c8fe15a3bf93a23088bcf1a56a0fa391d4e50
Author:     Valentin Schneider <valentin.schneider@arm.com>
AuthorDate: Wed, 4 Jul 2018 11:17:46 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 10 Sep 2018 11:05:52 +0200

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>
---
 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 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
 	}