FAILED: patch "[PATCH] sched/deadline: Fix BUG_ON condition for deboosted tasks" failed to apply to 4.19-stable tree

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ddfc710395cccc61247348df9eb18ea50321cbed Mon Sep 17 00:00:00 2001
From: Juri Lelli <[email protected]>
Date: Thu, 14 Jul 2022 17:19:08 +0200
Subject: [PATCH] sched/deadline: Fix BUG_ON condition for deboosted tasks

Tasks the are being deboosted from SCHED_DEADLINE might enter enqueue_task_dl() one last time and hit an erroneous BUG_ON condition:
since they are not boosted anymore, the if (is_dl_boosted()) branch is not taken, but the else if (!dl_prio) is and inside this one we BUG_ON(!is_dl_boosted), which is of course false (BUG_ON triggered) otherwise we had entered the if branch above. Long story short, the current condition doesn't make sense and always leads to triggering of a BUG.

Fix this by only checking enqueue flags, properly: ENQUEUE_REPLENISH has to be present, but additional flags are not a problem.

index b5152961b743..7bf561262cb8 100644
@@ -1701,7 +1701,10 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
 		 * the throttle.
 		 */
 		p->dl.dl_throttled = 0;
-		BUG_ON(!is_dl_boosted(&p->dl) || flags != ENQUEUE_REPLENISH);
+		if (!(flags & ENQUEUE_REPLENISH))
+			printk_deferred_once("sched: DL de-boosted task PID %d: REPLENISH flag missing\n",
+					     task_pid_nr(p));
+
 		return;
 	}