linux-kernel - Re: [PATCH] Revert "sched/core: Tweak wait_task_inactive() to force dequeue sched

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Message-ID: <0fc0943c-8ec1-47dd-9b3a-82c68c6bde34@amd.com>
Date: Mon, 29 Sep 2025 09:23:06 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Matt Fleming <matt@...dmodwrite.com>
CC: John Stultz <jstultz@...gle.com>, Ingo Molnar <mingo@...hat.com>, "Peter
 Zijlstra" <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
	"Vincent Guittot" <vincent.guittot@...aro.org>, Dietmar Eggemann
	<dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall
	<bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Valentin Schneider
	<vschneid@...hat.com>, <linux-kernel@...r.kernel.org>,
	<kernel-team@...udflare.com>, Matt Fleming <mfleming@...udflare.com>, "Oleg
 Nesterov" <oleg@...hat.com>, Chris Arges <carges@...udflare.com>,
	<stable@...r.kernel.org>
Subject: Re: [PATCH] Revert "sched/core: Tweak wait_task_inactive() to force
 dequeue sched_delayed tasks"

Hello Matt,

On 9/26/2025 9:04 PM, Matt Fleming wrote:
> On Fri, Sep 26, 2025 at 3:43 AM K Prateek Nayak <kprateek.nayak@....com> wrote:
>>
>> Hello John, Matt,
>>
>> On 9/26/2025 5:35 AM, John Stultz wrote:
>>>
>>> However, there are two spots where we might exit dequeue_entities()
>>> early when cfs_rq_throttled(rq), so maybe that's what's catching us
>>> here?
>>
>> That could very likely be it.
> 
> That tracks -- we're heavy users of cgroups and this particular issue
> only appeared on our kubernetes nodes.
> 
>> Matt, if possible can you try the patch attached below to check if the
>> bailout for throttled hierarchy is indeed the root cause. Thanks in
>> advance.
> 
> I've been running our reproducer with this patch for the last few
> hours without any issues, so the fix looks good to me.
> 
> Tested-by: Matt Fleming <mfleming@...udflare.com>

Thank you for testing the diff. I see Ingo has already posted the
scheduler pull for v6.18 which indirectly solves this by removing those
early returns.

Once that lands, I'll attach a formal commit log and send out a patch
targeting the stable kernels >= 6.12.

-- 
Thanks and Regards,
Prateek