[PATCH] sched: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn

[Con Kolivas]

We should not be using smp_processor_id() with preempt enabled.

Bug identified and fix provided by Alfred Chen.

Signed-off-by: Con Kolivas <kernel@xxxxxxxxxxx>

---
 kernel/smpboot.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-4.7.3-ck3/kernel/smpboot.c
===================================================================
--- linux-4.7.3-ck3.orig/kernel/smpboot.c	2016-05-16 08:43:13.000000000 +1000
+++ linux-4.7.3-ck3/kernel/smpboot.c	2016-09-13 16:17:33.535655129 +1000
@@ -122,12 +122,12 @@ static int smpboot_thread_fn(void *data)
 
 		if (kthread_should_park()) {
 			__set_current_state(TASK_RUNNING);
-			preempt_enable();
 			if (ht->park && td->status == HP_THREAD_ACTIVE) {
 				BUG_ON(td->cpu != smp_processor_id());
 				ht->park(td->cpu);
 				td->status = HP_THREAD_PARKED;
 			}
+			preempt_enable();
 			kthread_parkme();
 			/* We might have been woken for stop */
 			continue;