sched: 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.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 682a98524cfe8fa1ebae12e2508578a9ab6ded0d..b15e2bb4cd424244c00302995f9f515141bafaae 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8271,7 +8271,7 @@ next_group:
                struct root_domain *rd = env->dst_rq->rd;
 
                /* update overload indicator if we are at root domain */
-               rd->overload = sg_status & SG_OVERLOAD;
+               WRITE_ONCE(rd->overload, sg_status & SG_OVERLOAD);
 
                /* Update over-utilization (tipping point, U >= 0) indicator */
                WRITE_ONCE(rd->overutilized, sg_status & SG_OVERUTILIZED);
@@ -9724,7 +9724,7 @@ 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 25057135ee6ecf0b95e3be1d88b4576f7fb11eb2..73d4432f66a220635b56ecc9ab5b4861f92e635f 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1720,8 +1720,8 @@ 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
        }