sched/core: Remove check of p->sched_class

Search all usage of p->sched_class in sched/core.c, no one check it
before use, so it seems that every task must belong to one sched_class.
Signed-off-by: Yao Dongdong <yaodongdong@huawei.com>
[ Moved the early class assignment to make it boot. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1419835303-28958-1-git-send-email-yaodongdong@huawei.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/core.c

@@ -4744,7 +4744,7 @@ static struct rq *move_queued_task(struct task_struct *p, int new_cpu)
 
 void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask)
 {
-	if (p->sched_class && p->sched_class->set_cpus_allowed)
+	if (p->sched_class->set_cpus_allowed)
 		p->sched_class->set_cpus_allowed(p, new_mask);
 
 	cpumask_copy(&p->cpus_allowed, new_mask);
@@ -7253,6 +7253,11 @@ void __init sched_init(void)
 	atomic_inc(&init_mm.mm_count);
 	enter_lazy_tlb(&init_mm, current);
 
+	/*
+	 * During early bootup we pretend to be a normal task:
+	 */
+	current->sched_class = &fair_sched_class;
+
 	/*
 	 * Make us the idle thread. Technically, schedule() should not be
 	 * called from this thread, however somewhere below it might be,
@@ -7263,11 +7268,6 @@ void __init sched_init(void)
 
 	calc_load_update = jiffies + LOAD_FREQ;
 
-	/*
-	 * During early bootup we pretend to be a normal task:
-	 */
-	current->sched_class = &fair_sched_class;
-
 #ifdef CONFIG_SMP
 	zalloc_cpumask_var(&sched_domains_tmpmask, GFP_NOWAIT);
 	/* May be allocated at isolcpus cmdline parse time */