[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 <ker...@kolivas.org>

---
 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;