1 files changed, 43 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 28c73f07efb2..8dcdec6fe0fe 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1052,6 +1052,49 @@ static void resched_cpu(int cpu)
         resched_task(cpu_curr(cpu));
         spin_unlock_irqrestore(&rq->lock, flags);
 }
+
+#ifdef CONFIG_NO_HZ
+/*
+ * When add_timer_on() enqueues a timer into the timer wheel of an
+ * idle CPU then this timer might expire before the next timer event
+ * which is scheduled to wake up that CPU. In case of a completely
+ * idle system the next event might even be infinite time into the
+ * future. wake_up_idle_cpu() ensures that the CPU is woken up and
+ * leaves the inner idle loop so the newly added timer is taken into
+ * account when the CPU goes back to idle and evaluates the timer
+ * wheel for the next timer event.
+ */
+void wake_up_idle_cpu(int cpu)
+{
+        struct rq *rq = cpu_rq(cpu);
+
+        if (cpu == smp_processor_id())
+                return;
+
+        /*
+         * This is safe, as this function is called with the timer
+         * wheel base lock of (cpu) held. When the CPU is on the way
+         * to idle and has not yet set rq->curr to idle then it will
+         * be serialized on the timer wheel base lock and take the new
+         * timer into account automatically.
+         */
+        if (rq->curr != rq->idle)
+                return;
+
+        /*
+         * We can set TIF_RESCHED on the idle task of the other CPU
+         * lockless. The worst case is that the other CPU runs the
+         * idle task through an additional NOOP schedule()
+         */
+        set_tsk_thread_flag(rq->idle, TIF_NEED_RESCHED);
+
+        /* NEED_RESCHED must be visible before we test polling */
+        smp_mb();
+        if (!tsk_is_polling(rq->idle))
+                smp_send_reschedule(cpu);
+}
+#endif
+
 #else
 static void __resched_task(struct task_struct *p, int tif_bit)
 {