[tip:sched/core] sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()

[tip-bot for Con Kolivas <tipbot@zytor.com>]

Commit-ID:  4fa5cd5245b627db88c9ca08ae442373b02596b4
Gitweb:     http://git.kernel.org/tip/4fa5cd5245b627db88c9ca08ae442373b02596b4
Author:     Con Kolivas <kernel@kolivas.org>
AuthorDate: Tue, 13 Sep 2016 16:27:05 +1000
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 22 Sep 2016 12:28:00 +0200

sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()

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

Bug identified and fix provided by Alfred Chen.

Reported-by: Alfred Chen <cchalpha@gmail.com>
Signed-off-by: Con Kolivas <kernel@kolivas.org>
Cc: Alfred Chen <cchalpha@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/2042051.3vvUWIM0vs@hex
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/smpboot.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 13bc43d..fc0d8270 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -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;