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Subject[tip: sched/urgent] sched/deadline: Fix BUG_ON condition for deboosted tasks
The following commit has been merged into the sched/urgent branch of tip:

Commit-ID: ddfc710395cccc61247348df9eb18ea50321cbed
Gitweb: https://git.kernel.org/tip/ddfc710395cccc61247348df9eb18ea50321cbed
Author: Juri Lelli <juri.lelli@redhat.com>
AuthorDate: Thu, 14 Jul 2022 17:19:08 +02:00
Committer: Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 21 Jul 2022 10:35:28 +02:00

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.

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

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index b515296..7bf5612 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -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;
}

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