sched: Update rq clock before migrating tasks out of dying CPU

Because the sched_class::put_prev_task() callback of rt and fair
classes are referring to the rq clock to update their runtime
statistics. There is a missing rq clock update from the CPU
hotplug notifier's entry point of the scheduler.

Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Li Zhong <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Paul Turner <[email protected]>
Cc: Mike Galbraith <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

kernel/sched/core.c

@@ -4378,6 +4378,13 @@ static void migrate_tasks(unsigned int dead_cpu)
 	 */
 	rq->stop = NULL;
 
+	/*
+	 * put_prev_task() and pick_next_task() sched
+	 * class method both need to have an up-to-date
+	 * value of rq->clock[_task]
+	 */
+	update_rq_clock(rq);
+
 	for ( ; ; ) {
 		/*
 		 * There's this thread running, bail when that's the only