block/ioprio: Use a helper to check for RT prio

A side-effect to the old code is that now SCHED_DEADLINE is also
recognized.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Jens Axboe <axboe@fb.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171004154901.26904-2-bigeasy@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/ioprio.h

@@ -2,6 +2,7 @@
 #define IOPRIO_H
 
 #include <linux/sched.h>
+#include <linux/sched/rt.h>
 #include <linux/iocontext.h>
 
 /*
@@ -62,7 +63,7 @@ static inline int task_nice_ioclass(struct task_struct *task)
 {
 	if (task->policy == SCHED_IDLE)
 		return IOPRIO_CLASS_IDLE;
-	else if (task->policy == SCHED_FIFO || task->policy == SCHED_RR)
+	else if (task_is_realtime(task))
 		return IOPRIO_CLASS_RT;
 	else
 		return IOPRIO_CLASS_BE;