linux-kernel - [PATCH 5.15 137/201] sched/deadline: Fix BUG

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Date:   Wed, 27 Jul 2022 18:10:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Juri Lelli <juri.lelli@...hat.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [PATCH 5.15 137/201] sched/deadline: Fix BUG_ON condition for deboosted tasks

From: Juri Lelli <juri.lelli@...hat.com>

commit ddfc710395cccc61247348df9eb18ea50321cbed upstream.

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.

Fixes: 64be6f1f5f71 ("sched/deadline: Don't replenish from a !SCHED_DEADLINE entity")
Signed-off-by: Juri Lelli <juri.lelli@...hat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20220714151908.533052-1-juri.lelli@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/sched/deadline.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1561,7 +1561,10 @@ static void enqueue_task_dl(struct rq *r
 		 * 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;
 	}