linux-kernel - Re: sched/fair: Kernel panics in pick_next

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Message-ID: <acad4ac6a2daea2884e8ae4d031dfc8ae30fc365.camel@gmx.de>
Date: Thu, 03 Oct 2024 11:31:06 +0200
From: Mike Galbraith <efault@....de>
To: Benjamin Segall <bsegall@...gle.com>
Cc: Vishal Chourasia <vishalc@...ux.ibm.com>, Peter Zijlstra
 <peterz@...radead.org>, linux-kernel@...r.kernel.org, Ingo Molnar
 <mingo@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, Juri
 Lelli <juri.lelli@...hat.com>, Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>,
 Valentin Schneider <vschneid@...hat.com>, luis.machado@....com
Subject: Re: sched/fair: Kernel panics in pick_next_entity

On Thu, 2024-10-03 at 06:41 +0200, Mike Galbraith wrote:
> On Wed, 2024-10-02 at 15:31 -0700, Benjamin Segall wrote:

> > Whether dequeue_entity + enqueue_entity is better or worse than
> > requeue_delayed_entity (+break), I really don't know.
>
> Hm, I'd say requeue_delayed_entity() not only fits better, it using
> less lines gives it an extra brownie point.

Probable not worth any churn or effort, but it is an option.

sched: Clean up sched_delayed handling in unthrottle_cfs_rq()

requeue_delayed_entity() achieves and documents in one line what a less
clear preparatory dequeue facilitates over several, so use it instead,
and remove the superfluous comment.

Signed-off-by: Mike Galbraith <efault@....de>
---
 kernel/sched/fair.c |    9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6058,12 +6058,9 @@ void unthrottle_cfs_rq(struct cfs_rq *cf
 	for_each_sched_entity(se) {
 		struct cfs_rq *qcfs_rq = cfs_rq_of(se);

-		/* 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)
+		if (se->sched_delayed)
+			requeue_delayed_entity(se);
+		if (se->on_rq)
 			break;
 		enqueue_entity(qcfs_rq, se, ENQUEUE_WAKEUP);