[PATCH 1/4] kthreads: move sched-realeted initialization from kthreadd context

[Oleg Nesterov <oleg@redhat.com>]

(on top of kthread-dont-looking-for-a-task-in-create_kthread-2.patch)

kthreadd is the single thread which implements ths "create" request,
move sched_setscheduler/etc from create_kthread() to kthread_create()
to improve the scalability.

We should be careful with sched_setscheduler(), use _nochek helper.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

--- 6.29-rc3/kernel/kthread.c~1_SCHED	2009-01-30 09:40:12.000000000 +0100
+++ 6.29-rc3/kernel/kthread.c	2009-01-30 09:46:29.000000000 +0100
@@ -100,15 +100,7 @@ static void create_kthread(struct kthrea
 	if (pid < 0) {
 		create->result = ERR_PTR(pid);
 	} else {
-		struct sched_param param = { .sched_priority = 0 };
 		wait_for_completion(&create->started);
-		/*
-		 * root may have changed our (kthreadd's) priority or CPU mask.
-		 * The kernel thread should not inherit these properties.
-		 */
-		sched_setscheduler(create->result, SCHED_NORMAL, &param);
-		set_user_nice(create->result, KTHREAD_NICE_LEVEL);
-		set_cpus_allowed_ptr(create->result, CPU_MASK_ALL_PTR);
 	}
 	complete(&create->done);
 }
@@ -152,11 +144,20 @@ struct task_struct *kthread_create(int (
 	wait_for_completion(&create.done);
 
 	if (!IS_ERR(create.result)) {
+		struct sched_param param = { .sched_priority = 0 };
 		va_list args;
+
 		va_start(args, namefmt);
 		vsnprintf(create.result->comm, sizeof(create.result->comm),
 			  namefmt, args);
 		va_end(args);
+		/*
+		 * root may have changed our (kthreadd's) priority or CPU mask.
+		 * The kernel thread should not inherit these properties.
+		 */
+		sched_setscheduler_nocheck(create.result, SCHED_NORMAL, &param);
+		set_user_nice(create.result, KTHREAD_NICE_LEVEL);
+		set_cpus_allowed_ptr(create.result, CPU_MASK_ALL_PTR);
 	}
 	return create.result;
 }