sched: Update rq clock before calling check_preempt_curr()

check_preempt_curr() of fair class needs an uptodate sched clock
value to update runtime stats of the current task of the target's rq.

When a task is woken up, activate_task() is usually called right before
ttwu_do_wakeup() unless the task is still in the runqueue. In the latter
case we need to update the rq clock explicitly because activate_task()
isn't here to do the job for us.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul Turner <pjt@google.com>
Cc: Mike Galbraith <efault@gmx.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1365724262-20142-4-git-send-email-fweisbec@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -1365,6 +1365,8 @@ static int ttwu_remote(struct task_struct *p, int wake_flags)
 
 	rq = __task_rq_lock(p);
 	if (p->on_rq) {
+		/* check_preempt_curr() may use rq clock */
+		update_rq_clock(rq);
 		ttwu_do_wakeup(rq, p, wake_flags);
 		ret = 1;
 	}