[RFC PATCH 12/19] sched/fair: Reorder the barrier in nohz_balance_enter_idle()

[K Prateek Nayak <kprateek.nayak@amd.com>]

The smp_mb__after_atomic() in nohz_balance_enter_idle() is used to order
the setting of the nohz idle CPU on the "nohz.idle_cpus_mask" with the
write to "nohz.needs_update" as per the comment.

Since set_cpu_sd_state_idle() is now responsible for idle tracking using
"sd_nohz->shared", reorder the call to set_cpu_sd_state_idle() to come
before the barrier ensuring the CPU is tracked on the idle mask before
the update to "nohz.needs_update" is observed.

Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
 kernel/sched/fair.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c8226520758d..d13de6feb467 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -12544,6 +12544,8 @@ void nohz_balance_enter_idle(int cpu)
 	cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
 	atomic_inc(&nohz.nr_cpus);
 
+	set_cpu_sd_state_idle(cpu);
+
 	/*
 	 * Ensures that if nohz_idle_balance() fails to observe our
 	 * @idle_cpus_mask store, it must observe the @has_blocked
@@ -12551,8 +12553,6 @@ void nohz_balance_enter_idle(int cpu)
 	 */
 	smp_mb__after_atomic();
 
-	set_cpu_sd_state_idle(cpu);
-
 	WRITE_ONCE(nohz.needs_update, 1);
 out:
 	/*
-- 
2.34.1