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") Cc: stable@vger.kernel.org Signed-off-by: Juri Lelli juri.lelli@redhat.com
--- v1->v2 - Make detection of faulty condition less fatal [Peter Zijlstra] - Cc stable and update fixes tag [Srivatsa S. Bhat] --- 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 5867e186c39a..0ab79d819a0d 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1703,7 +1703,10 @@ 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; }