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 stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From ddfc710395cccc61247348df9eb18ea50321cbed Mon Sep 17 00:00:00 2001 From: Juri Lelli juri.lelli@redhat.com 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.
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
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index b5152961b743..7bf561262cb8 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; }