"sd->nohz_idle" currently relies on the fact that it is always modified
from the local CPU to keep consistency however, the subsequent commits
will use the rq->online() callback to correct the "sd->nohz_idle" status
from a remote CPU during sched domain rebuild.

Use xchg() instead to prevent double accounting of "nr_busy_cpus" if the
status update on the local CPU races with a correction from a remote
CPU.

No functional changes intended.

Reviewed-by: Gautham R. Shenoy <gautham.shenoy@amd.com>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
 kernel/sched/fair.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e3935903d9c5..3128daf1d5d4 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12559,7 +12559,9 @@ static void set_cpu_sd_state_busy(int cpu)
 	if (!sd || !sd->nohz_idle)
 		return;
 
-	sd->nohz_idle = 0;
+	if (!xchg(&sd->nohz_idle, 0))
+		return;
+
 	atomic_inc(&sd->shared->nr_busy_cpus);
 }
 
@@ -12587,7 +12589,9 @@ static void set_cpu_sd_state_idle(int cpu)
 	if (!sd || sd->nohz_idle)
 		return;
 
-	sd->nohz_idle = 1;
+	if (xchg(&sd->nohz_idle, 1))
+		return;
+
 	atomic_dec(&sd->shared->nr_busy_cpus);
 }
 
-- 
2.43.0