sched/deadline: Use revised wakeup rule for dl_server

John noted that commit 1151354 ("sched/deadline: Fix 'stuck' dl_server")
unfixed the issue from commit a3a70ca ("sched/deadline: Fix dl_server
behaviour").

The issue in commit 1151354 was for wakeups of the server after the
deadline; in which case you *have* to start a new period. The case for
a3a70ca is wakeups before the deadline.

Now, because the server is effectively running a least-laxity policy, it means
that any wakeup during the runnable phase means dl_entity_overflow() will be
true. This means we need to adjust the runtime to allow it to still run until
the existing deadline expires.

Use the revised wakeup rule for dl_defer entities.

Fixes: 1151354 ("sched/deadline: Fix 'stuck' dl_server")
Reported-by: John Stultz <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Acked-by: Juri Lelli <[email protected]>
Tested-by: John Stultz <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: Peter Zijlstra

kernel/sched/deadline.c

@@ -1027,7 +1027,7 @@ static void update_dl_entity(struct sched_dl_entity *dl_se)
 	if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
 	    dl_entity_overflow(dl_se, rq_clock(rq))) {
 
-		if (unlikely(!dl_is_implicit(dl_se) &&
+		if (unlikely((!dl_is_implicit(dl_se) || dl_se->dl_defer) &&
 			     !dl_time_before(dl_se->deadline, rq_clock(rq)) &&
 			     !is_dl_boosted(dl_se))) {
 			update_dl_revised_wakeup(dl_se, rq);