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: <c8c28050-8c6e-45b1-8b70-06cf5e0921e6@linux.vnet.ibm.com>
Date: Thu, 19 Sep 2024 20:09:25 +0530
From: Venkat Rao Bagalkote <venkat88@...ux.vnet.ibm.com>
To: Mike Galbraith <efault@....de>, 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

Hello Mike,

Thanks for the patch. I applied your patch and verified the issue, and 
can confirm your patch fixes the issue.


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>


Regards,

Venkat.

On 19/09/24 11:39 am, Mike Galbraith wrote:
> On Mon, 2024-09-16 at 12:00 +0530, Venkat Rao Bagalkote wrote:
>> Greetings!!!
> Greetings,
>
>> I am seeing below kernel crash from 6.11.0-rc4-next-20240820.
>>
>>
>> Tried to do git bisect, but it didnt point to right patch. Attached is
>> the bisect log.
>>
>> Any help in fixing this is much appriciated.
> I met this, as well as other ways the wheels can fall off that turned
> out to have the same root.  I gave Peter a heads up with diag offline,
> but having now convinced myself that all is well, I'll go ahead and
> post a patchlet.
>
> At the very least it's worth putting out for wider testing.. and should
> anyone have something prettier in mind, yeah, do that instead.
>
> 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")
> Signed-off-by: Mike Galbraith <efault@....de>
> ---
>   kernel/sched/fair.c |   10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6049,10 +6049,14 @@ 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);
> -			break;
> +		/* Handle any unfinished DELAY_DEQUEUE business first. */
> +		if (unlikely(se->on_rq && se->sched_delayed)) {
> +			int flags = DEQUEUE_SLEEP | DEQUEUE_SPECIAL;
> +
> +			dequeue_entity(qcfs_rq, se, flags | DEQUEUE_DELAYED);
>   		}
> +		if (se->on_rq)
> +			break;
>   		enqueue_entity(qcfs_rq, se, ENQUEUE_WAKEUP);
>
>   		if (cfs_rq_is_idle(group_cfs_rq(se)))
>
>