1 files changed, 17 insertions, 0 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index d7f07a2da5a6..63aa50d7ce1e 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -308,6 +308,23 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
         }
         smpboot_park_threads(cpu);
 
+        /*
+         * By now 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 explicitly call both.
+         */
+#ifdef CONFIG_PREEMPT
+        synchronize_sched();
+#endif
+        synchronize_rcu();
+
+        /*
+         * So now all preempt/rcu users must observe !cpu_active().
+         */
+
         err = __stop_machine(take_cpu_down, &tcd_param, cpumask_of(cpu));
         if (err) {
                 /* CPU didn't die: tell everyone.  Can't complain. */