linux-kernel - [GIT PULL] scheduler fix

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Date:	Thu, 14 Jul 2016 20:56:33 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [GIT PULL] scheduler fix

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

   # HEAD: d60585c5766e9620d5d83e2b25dc042c7bdada2c sched/core: Correct off by one bug in load migration calculation

Fix a CPU hotplug related corruption of the load average that got introduced in 
this merge window.

 Thanks,

	Ingo

------------------>
Thomas Gleixner (1):
      sched/core: Correct off by one bug in load migration calculation


 kernel/sched/core.c    | 6 ++++--
 kernel/sched/loadavg.c | 8 ++++----
 kernel/sched/sched.h   | 2 +-
 3 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 51d7105f529a..97ee9ac7e97c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5394,13 +5394,15 @@ void idle_task_exit(void)
 /*
  * Since this CPU is going 'away' for a while, fold any nr_active delta
  * we might have. Assumes we're called after migrate_tasks() so that the
- * nr_active count is stable.
+ * nr_active count is stable. We need to take the teardown thread which
+ * is calling this into account, so we hand in adjust = 1 to the load
+ * calculation.
  *
  * Also see the comment "Global load-average calculations".
  */
 static void calc_load_migrate(struct rq *rq)
 {
-	long delta = calc_load_fold_active(rq);
+	long delta = calc_load_fold_active(rq, 1);
 	if (delta)
 		atomic_long_add(delta, &calc_load_tasks);
 }
diff --git a/kernel/sched/loadavg.c b/kernel/sched/loadavg.c
index b0b93fd33af9..a2d6eb71f06b 100644
--- a/kernel/sched/loadavg.c
+++ b/kernel/sched/loadavg.c
@@ -78,11 +78,11 @@ void get_avenrun(unsigned long *loads, unsigned long offset, int shift)
 	loads[2] = (avenrun[2] + offset) << shift;
 }
 
-long calc_load_fold_active(struct rq *this_rq)
+long calc_load_fold_active(struct rq *this_rq, long adjust)
 {
 	long nr_active, delta = 0;
 
-	nr_active = this_rq->nr_running;
+	nr_active = this_rq->nr_running - adjust;
 	nr_active += (long)this_rq->nr_uninterruptible;
 
 	if (nr_active != this_rq->calc_load_active) {
@@ -188,7 +188,7 @@ void calc_load_enter_idle(void)
 	 * We're going into NOHZ mode, if there's any pending delta, fold it
 	 * into the pending idle delta.
 	 */
-	delta = calc_load_fold_active(this_rq);
+	delta = calc_load_fold_active(this_rq, 0);
 	if (delta) {
 		int idx = calc_load_write_idx();
 
@@ -389,7 +389,7 @@ void calc_global_load_tick(struct rq *this_rq)
 	if (time_before(jiffies, this_rq->calc_load_update))
 		return;
 
-	delta  = calc_load_fold_active(this_rq);
+	delta  = calc_load_fold_active(this_rq, 0);
 	if (delta)
 		atomic_long_add(delta, &calc_load_tasks);
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 7cbeb92a1cb9..898c0d2f18fe 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -28,7 +28,7 @@ extern unsigned long calc_load_update;
 extern atomic_long_t calc_load_tasks;
 
 extern void calc_global_load_tick(struct rq *this_rq);
-extern long calc_load_fold_active(struct rq *this_rq);
+extern long calc_load_fold_active(struct rq *this_rq, long adjust);
 
 #ifdef CONFIG_SMP
 extern void cpu_load_update_active(struct rq *this_rq);