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>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2301793..d9c4e97 100644 (file)
--- 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 4d18147..9380636 100644 (file)
--- 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
        }