From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:30:27 -0500
Subject: stop_machine: convert stop_machine_run() to PREEMPT_RT
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz

Instead of playing with non-preemption, introduce explicit
startup serialization. This is more robust and cleaner as
well.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bigeasy: XXX: stopper_lock -> stop_cpus_lock]
---
 kernel/stop_machine.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -452,6 +452,16 @@ static void cpu_stopper_thread(unsigned
 		struct cpu_stop_done *done = work->done;
 		int ret;
 
+		/*
+		 * Wait until the stopper finished scheduling on all
+		 * cpus
+		 */
+		lg_global_lock(&stop_cpus_lock);
+		/*
+		 * Let other cpu threads continue as well
+		 */
+		lg_global_unlock(&stop_cpus_lock);
+
 		/* cpu stop callbacks must not sleep, make in_atomic() == T */
 		preempt_count_inc();
 		ret = fn(arg);
