linux-kernel - Re: [patch] Re: [PowerPC][Linux-next][6.11.0-rc4-next-20240820] OOPs while running LTP FS Stress

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Message-ID: <177646b0c427786c90a8ccb67f5b956a12759d3a.camel@gmx.de>
Date: Fri, 20 Sep 2024 04:15:30 +0200
From: Mike Galbraith <efault@....de>
To: Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>, 
 linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, 
 peterz@...radead.org, vschneid@...hat.com, mingo@...nel.org,
 sfr@...b.auug.org.au
Subject: Re: [patch] Re: [PowerPC][Linux-next][6.11.0-rc4-next-20240820]
 OOPs while running LTP FS Stress

On Thu, 2024-09-19 at 20:09 +0530, Venkat Rao Bagalkote wrote:
>
> Please add the below tags.
>
>
> Reported-by: Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>
>
> Tested-by: Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>

Sure, and while at it I can brush patchlet's rather scruffy fur.

1. on_rq being implied by sched_delayed, redundant check can go.
2. no tasks anywhere in sight, DEQUEUE_SPECIAL can go.
3. use of unlikely in an unlikely path can also go.
No functional change.  Too bad everything around there fits in 80
characters, or a couple useless diffstat plus signs could go too.

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
@@ -6049,10 +6049,13 @@ 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)))