patches/preempt-lazy-check-preempt_schedule.patch

From d3fe5ab82185b96daa4608b5ec8e98801747660e Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 20 Jan 2016 15:13:30 +0100
Subject: [PATCH] preempt-lazy: Add the lazy-preemption check to
 preempt_schedule()

Probably in the rebase onto v4.1 this check got moved into less commonly used
preempt_schedule_notrace(). This patch ensures that both functions use it.

Reported-by: Mike Galbraith <umgwanakikbuti@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ec1fd53d3b11..90d88786cfda 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3621,6 +3621,30 @@ static void __sched notrace preempt_schedule_common(void)
 	} while (need_resched());
 }
 
+#ifdef CONFIG_PREEMPT_LAZY
+/*
+ * If TIF_NEED_RESCHED is then we allow to be scheduled away since this is
+ * set by a RT task. Oterwise we try to avoid beeing scheduled out as long as
+ * preempt_lazy_count counter >0.
+ */
+static __always_inline int preemptible_lazy(void)
+{
+	if (test_thread_flag(TIF_NEED_RESCHED))
+		return 1;
+	if (current_thread_info()->preempt_lazy_count)
+		return 0;
+	return 1;
+}
+
+#else
+
+static int preemptible_lazy(void)
+{
+	return 1;
+}
+
+#endif
+
 #ifdef CONFIG_PREEMPT
 /*
  * this is the entry point to schedule() from in-kernel preemption
@@ -3635,6 +3659,8 @@ asmlinkage __visible void __sched notrace preempt_schedule(void)
 	 */
 	if (likely(!preemptible()))
 		return;
+	if (!preemptible_lazy())
+		return;
 
 	preempt_schedule_common();
 }
@@ -3661,15 +3687,9 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
 
 	if (likely(!preemptible()))
 		return;
-
-#ifdef CONFIG_PREEMPT_LAZY
-	/*
-	 * Check for lazy preemption
-	 */
-	if (current_thread_info()->preempt_lazy_count &&
-	    !test_thread_flag(TIF_NEED_RESCHED))
+	if (!preemptible_lazy())
 		return;
-#endif
+
 	do {
 		/*
 		 * Because the function tracer can trace preempt_count_sub()
-- 
2.5.0