FROMLIST: 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>
Change-Id: I2b35baaebb9a55afa7877b049d2af1c255567601

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 9086e4d..ab8bfd2 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -8640,8 +8640,8 @@ 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);
 
                /* Update over-utilization (tipping point, U >= 0) indicator */
                if (READ_ONCE(env->dst_rq->rd->overutilized) != overutilized)
@@ -10096,7 +10096,7 @@ 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 15f5253..90e9386 100644 (file)
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1691,8 +1691,8 @@ 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
        }