sched/rt, sched/dl: Don't push if task's scheduling class was changed

We got this warning:

    WARNING: CPU: 1 PID: 2468 at kernel/sched/core.c:1161 set_task_cpu+0x1af/0x1c0
    [...]
    Call Trace:

    dump_stack+0x63/0x87
    __warn+0xd1/0xf0
    warn_slowpath_null+0x1d/0x20
    set_task_cpu+0x1af/0x1c0
    push_dl_task.part.34+0xea/0x180
    push_dl_tasks+0x17/0x30
    __balance_callback+0x45/0x5c
    __sched_setscheduler+0x906/0xb90
    SyS_sched_setattr+0x150/0x190
    do_syscall_64+0x62/0x110
    entry_SYSCALL64_slow_path+0x25/0x25

This corresponds to:

    WARN_ON_ONCE(p->state == TASK_RUNNING &&
             p->sched_class == &fair_sched_class &&
             (p->on_rq && !task_on_rq_migrating(p)))

It happens because in find_lock_later_rq(), the task whose scheduling
class was changed to fair class is still pushed away as if it were
a deadline task ...

So, check in find_lock_later_rq() after double_lock_balance(), if the
scheduling class of the deadline task was changed, break and retry.

Apply the same logic to RT tasks.
Signed-off-by: Xunlei Pang <xlpang@redhat.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Juri Lelli <juri.lelli@arm.com>
Link: http://lkml.kernel.org/r/1462767091-1215-1-git-send-email-xlpang@redhat.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/deadline.c

@@ -1394,6 +1394,7 @@ static struct rq *find_lock_later_rq(struct task_struct *task, struct rq *rq)
 				     !cpumask_test_cpu(later_rq->cpu,
 				                       &task->cpus_allowed) ||
 				     task_running(rq, task) ||
+				     !dl_task(task) ||
 				     !task_on_rq_queued(task))) {
 				double_unlock_balance(rq, later_rq);
 				later_rq = NULL;

kernel/sched/rt.c

@@ -1729,6 +1729,7 @@ static struct rq *find_lock_lowest_rq(struct task_struct *task, struct rq *rq)
 				     !cpumask_test_cpu(lowest_rq->cpu,
 						       tsk_cpus_allowed(task)) ||
 				     task_running(rq, task) ||
+				     !rt_task(task) ||
 				     !task_on_rq_queued(task))) {
 
 				double_unlock_balance(rq, lowest_rq);