sched/hotplug: Move sync_rcu to be with set_cpu_active(false)
The sync_rcu stuff is specificically for clearing bits in the active
mask, such that everybody will observe the bit cleared and will not
consider the cleared CPU for load-balancing etc.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: rt@linutronix.de
Link: http://lkml.kernel.org/r/20160310120025.169219710@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 73bcd93..0a31078 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7112,6 +7112,20 @@
int ret;
set_cpu_active(cpu, false);
+ /*
+ * We've cleared cpu_active_mask, wait for all preempt-disabled and RCU
+ * users of this state to go away such that all new such users will
+ * observe it.
+ *
+ * For CONFIG_PREEMPT we have preemptible RCU and its sync_rcu() might
+ * not imply sync_sched(), so wait for both.
+ *
+ * Do sync before park smpboot threads to take care the rcu boost case.
+ */
+ if (IS_ENABLED(CONFIG_PREEMPT))
+ synchronize_rcu_mult(call_rcu, call_rcu_sched);
+ else
+ synchronize_rcu();
if (!sched_smp_initialized)
return 0;
