sched, sched_ext: Simplify dl_prio() case handling in sched_fork()

sched_fork() returns with -EAGAIN if dl_prio(@p). a7a9fc54 ("sched_ext:
Add boilerplate for extensible scheduler class") added scx_pre_fork() call
before it and then scx_cancel_fork() on the exit path. This is silly as the
dl_prio() block can just be moved above the scx_pre_fork() call.

Move the dl_prio() block above the scx_pre_fork() call and remove the now
unnecessary scx_cancel_fork() invocation.
Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: David Vernet <void@manifault.com>

kernel/sched/core.c

@@ -4580,8 +4580,6 @@ late_initcall(sched_core_sysctl_init);
  */
 int sched_fork(unsigned long clone_flags, struct task_struct *p)
 {
-	int ret;
-
 	__sched_fork(clone_flags, p);
 	/*
 	 * We mark the process as NEW here. This guarantees that
@@ -4618,12 +4616,12 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 		p->sched_reset_on_fork = 0;
 	}
 
+	if (dl_prio(p->prio))
+		return -EAGAIN;
+
 	scx_pre_fork(p);
 
-	if (dl_prio(p->prio)) {
-		ret = -EAGAIN;
-		goto out_cancel;
-	} else if (rt_prio(p->prio)) {
+	if (rt_prio(p->prio)) {
 		p->sched_class = &rt_sched_class;
 #ifdef CONFIG_SCHED_CLASS_EXT
 	} else if (task_should_scx(p)) {
@@ -4649,10 +4647,6 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 	RB_CLEAR_NODE(&p->pushable_dl_tasks);
 #endif
 	return 0;
-
-out_cancel:
-	scx_cancel_fork(p);
-	return ret;
 }
 
 int sched_cgroup_fork(struct task_struct *p, struct kernel_clone_args *kargs)