sched: Drop rq->lock from first part of wake_up_new_task()

Since p->pi_lock now protects all things needed to call
select_task_rq() avoid the double remote rq->lock acquisition and rely
on p->pi_lock.

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]>

Author: Peter Zijlstra

kernel/sched.c

@@ -2736,28 +2736,18 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
 {
 	unsigned long flags;
 	struct rq *rq;
-	int cpu __maybe_unused = get_cpu();
 
+	raw_spin_lock_irqsave(&p->pi_lock, flags);
 #ifdef CONFIG_SMP
-	rq = task_rq_lock(p, &flags);
-	p->state = TASK_WAKING;
-
 	/*
 	 * Fork balancing, do it here and not earlier because:
 	 *  - cpus_allowed can change in the fork path
 	 *  - any previously selected cpu might disappear through hotplug
-	 *
-	 * We set TASK_WAKING so that select_task_rq() can drop rq->lock
-	 * without people poking at ->cpus_allowed.
 	 */
-	cpu = select_task_rq(p, SD_BALANCE_FORK, 0);
-	set_task_cpu(p, cpu);
-
-	p->state = TASK_RUNNING;
-	task_rq_unlock(rq, p, &flags);
+	set_task_cpu(p, select_task_rq(p, SD_BALANCE_FORK, 0));
 #endif
 
-	rq = task_rq_lock(p, &flags);
+	rq = __task_rq_lock(p);
 	activate_task(rq, p, 0);
 	p->on_rq = 1;
 	trace_sched_wakeup_new(p, true);
@@ -2767,7 +2757,6 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
 		p->sched_class->task_woken(rq, p);
 #endif
 	task_rq_unlock(rq, p, &flags);
-	put_cpu();
 }
 
 #ifdef CONFIG_PREEMPT_NOTIFIERS