linux-kernel - [patch] sched: Fix sched_delayed vs cfs

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Message-ID: <7515d2e64c989b9e3b828a9e21bcd959b99df06a.camel@gmx.de>
Date: Tue, 01 Oct 2024 03:34:01 +0200
From: Mike Galbraith <efault@....de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Venkat Rao Bagalkote
	 <venkat88@...ux.vnet.ibm.com>
Subject: [patch] sched: Fix sched_delayed vs cfs_bandwidth


Meeting an unfinished DELAY_DEQUEUE treated entity in unthrottle_cfs_rq()
leads to a couple terminal scenarios.  Finish it first, so ENQUEUE_WAKEUP
can proceed as it would have sans DELAY_DEQUEUE treatment.

Fixes: 152e11f6df29 ("sched/fair: Implement delayed dequeue")
Reported-by: Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>
Tested-by: Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>
Signed-off-by: Mike Galbraith <efault@....de>
---
 kernel/sched/fair.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6058,10 +6058,13 @@ void unthrottle_cfs_rq(struct cfs_rq *cf
 	for_each_sched_entity(se) {
 		struct cfs_rq *qcfs_rq = cfs_rq_of(se);

-		if (se->on_rq) {
-			SCHED_WARN_ON(se->sched_delayed);
+		/* Handle any unfinished DELAY_DEQUEUE business first. */
+		if (se->sched_delayed) {
+			int flags = DEQUEUE_SLEEP | DEQUEUE_DELAYED;
+
+			dequeue_entity(qcfs_rq, se, flags);
+		} else if (se->on_rq)
 			break;
-		}
 		enqueue_entity(qcfs_rq, se, ENQUEUE_WAKEUP);

 		if (cfs_rq_is_idle(group_cfs_rq(se)))