1 files changed, 48 insertions, 6 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index bbaf6e5d1d0..6a0197adad8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -520,7 +520,7 @@ static inline void init_hrtick(void)
  	__old;								\
 })
 
-#ifdef TIF_POLLING_NRFLAG
+#if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
 /*
  * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
  * this avoids any races wrt polling state changes and thereby avoids
@@ -531,12 +531,44 @@ static bool set_nr_and_not_polling(struct task_struct *p)
 	struct thread_info *ti = task_thread_info(p);
 	return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
 }
+
+/*
+ * Atomically set TIF_NEED_RESCHED if TIF_POLLING_NRFLAG is set.
+ *
+ * If this returns true, then the idle task promises to call
+ * sched_ttwu_pending() and reschedule soon.
+ */
+static bool set_nr_if_polling(struct task_struct *p)
+{
+	struct thread_info *ti = task_thread_info(p);
+	typeof(ti->flags) old, val = ACCESS_ONCE(ti->flags);
+
+	for (;;) {
+		if (!(val & _TIF_POLLING_NRFLAG))
+			return false;
+		if (val & _TIF_NEED_RESCHED)
+			return true;
+		old = cmpxchg(&ti->flags, val, val | _TIF_NEED_RESCHED);
+		if (old == val)
+			break;
+		val = old;
+	}
+	return true;
+}
+
 #else
 static bool set_nr_and_not_polling(struct task_struct *p)
 {
 	set_tsk_need_resched(p);
 	return true;
 }
+
+#ifdef CONFIG_SMP
+static bool set_nr_if_polling(struct task_struct *p)
+{
+	return false;
+}
+#endif
 #endif
 
 /*
@@ -1390,13 +1422,17 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
 }
 
 #ifdef CONFIG_SMP
-static void sched_ttwu_pending(void)
+void sched_ttwu_pending(void)
 {
 	struct rq *rq = this_rq();
 	struct llist_node *llist = llist_del_all(&rq->wake_list);
 	struct task_struct *p;
+	unsigned long flags;
 
-	raw_spin_lock(&rq->lock);
+	if (!llist)
+		return;
+
+	raw_spin_lock_irqsave(&rq->lock, flags);
 
 	while (llist) {
 		p = llist_entry(llist, struct task_struct, wake_entry);
@@ -1404,7 +1440,7 @@ static void sched_ttwu_pending(void)
 		ttwu_do_activate(rq, p, 0);
 	}
 
-	raw_spin_unlock(&rq->lock);
+	raw_spin_unlock_irqrestore(&rq->lock, flags);
 }
 
 void scheduler_ipi(void)
@@ -1451,8 +1487,14 @@ void scheduler_ipi(void)
 
 static void ttwu_queue_remote(struct task_struct *p, int cpu)
 {
-	if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list))
-		smp_send_reschedule(cpu);
+	struct rq *rq = cpu_rq(cpu);
+
+	if (llist_add(&p->wake_entry, &cpu_rq(cpu)->wake_list)) {
+		if (!set_nr_if_polling(rq->idle))
+			smp_send_reschedule(cpu);
+		else
+			trace_sched_wake_idle_without_ipi(cpu);
+	}
 }
 
 bool cpus_share_cache(int this_cpu, int that_cpu)