sched: Remove need_migrate_task()

Oleg noticed that need_migrate_task() doesn't need the ->on_cpu check
now that ttwu() doesn't do remote enqueues for !->on_rq && ->on_cpu,
so remove the helper and replace the single instance with a direct
->on_rq test.

Suggested-by: Oleg Nesterov <[email protected]>
Reviewed-by: Frank Rowand <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Nick Piggin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Andrew Morton <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

kernel/sched.c

@@ -2198,21 +2198,6 @@ struct migration_arg {
 
 static int migration_cpu_stop(void *data);
 
-/*
- * The task's runqueue lock must be held.
- * Returns true if you have to wait for migration thread.
- */
-static bool need_migrate_task(struct task_struct *p)
-{
-	/*
-	 * If the task is not on a runqueue (and not running), then
-	 * the next wake-up will properly place the task.
-	 */
-	bool running = p->on_rq || p->on_cpu;
-	smp_rmb(); /* finish_lock_switch() */
-	return running;
-}
-
 /*
  * wait_task_inactive - wait for a thread to unschedule.
  *
@@ -5985,7 +5970,7 @@ int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask)
 		goto out;
 
 	dest_cpu = cpumask_any_and(cpu_active_mask, new_mask);
-	if (need_migrate_task(p)) {
+	if (p->on_rq) {
 		struct migration_arg arg = { p, dest_cpu };
 		/* Need help from migration thread: drop lock and wait. */
 		task_rq_unlock(rq, p, &flags);