kthreads: fix softirq startup hang

In -rt where the timer softirq is forced threaded the
schedule_timeout_uninterruptible() might never return when the timer
softirq has not been started yet. Use schedule_hrtimeout() instead
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

kernel/sched.c

@@ -2156,7 +2156,10 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state)
 		 * yield - it could be a while.
 		 */
 		if (unlikely(on_rq)) {
-			schedule_timeout_uninterruptible(1);
+			ktime_t to = ktime_set(0, NSEC_PER_SEC/HZ);
+
+			set_current_state(TASK_UNINTERRUPTIBLE);
+			schedule_hrtimeout(&to, HRTIMER_MODE_REL);
 			continue;
 		}