sched/deadline: Don't replenish from a !SCHED_DEADLINE entity

In the deboost path, right after the dl_boosted flag has been
reset, we can currently end up replenishing using -deadline
parameters of a !SCHED_DEADLINE entity. This of course causes
a bug, as those parameters are empty.

In the case depicted above it is safe to simply bail out, as
the deboosted task is going to be back to its original scheduling
class anyway.

Reported-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Tested-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
Signed-off-by: Juri Lelli <juri.lelli@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: vincent@legout.info
Cc: Dario Faggioli <raistlin@linux.it>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Cc: Fabio Checconi <fchecconi@gmail.com>
Link: http://lkml.kernel.org/r/1414142198-18552-4-git-send-email-juri.lelli@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/deadline.c

@@ -847,8 +847,19 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
 	 * smaller than our one... OTW we keep our runtime and
 	 * deadline.
 	 */
-	if (pi_task && p->dl.dl_boosted && dl_prio(pi_task->normal_prio))
+	if (pi_task && p->dl.dl_boosted && dl_prio(pi_task->normal_prio)) {
 		pi_se = &pi_task->dl;
+	} else if (!dl_prio(p->normal_prio)) {
+		/*
+		 * Special case in which we have a !SCHED_DEADLINE task
+		 * that is going to be deboosted, but exceedes its
+		 * runtime while doing so. No point in replenishing
+		 * it, as it's going to return back to its original
+		 * scheduling class after this.
+		 */
+		BUG_ON(!p->dl.dl_boosted || flags != ENQUEUE_REPLENISH);
+		return;
+	}
 
 	/*
 	 * If p is throttled, we do nothing. In fact, if it exhausted