linux-kernel - [GIT pull] sched fix for 4.9

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Date:   Sat, 8 Oct 2016 14:54:06 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [GIT pull] sched fix for 4.9

Linus,

please pull the latest sched-urgent-for-linus git tree from:

   git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus

A revert of a commit which pointelessly widened a preempt disabled section
which in turn caused might_sleep() to trigger. The patch intended to
prevent usage of smp_processor_id() in preemptible context, but the usage
in that case is fine because the thread is pinned on a single cpu and
therefore cannot be migrated off.

Thanks,

	tglx

------------------>
Ingo Molnar (1):
      Revert "sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()"


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

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index fc0d8270f69e..13bc43d1fb22 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;