linux-kernel - Re: [PATCH] sched/fair: Add null pointer check to pick_next

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Message-ID: <20250415080235.GK5600@noisy.programming.kicks-ass.net>
Date: Tue, 15 Apr 2025 10:02:35 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Rik van Riel <riel@...riel.com>
Cc: Chris Mason <clm@...a.com>, Pat Cody <pat@...cody.io>, mingo@...hat.com,
	juri.lelli@...hat.com, vincent.guittot@...aro.org,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, vschneid@...hat.com, linux-kernel@...r.kernel.org,
	patcody@...a.com, kernel-team@...a.com,
	Breno Leitao <leitao@...ian.org>
Subject: Re: [PATCH] sched/fair: Add null pointer check to pick_next_entity()

On Mon, Apr 14, 2025 at 03:57:42PM -0400, Rik van Riel wrote:
> On Wed, 2025-04-02 at 10:22 +0200, Peter Zijlstra wrote:
> > 
> > Please confirm what the reason for overflow is.
> > 
> Running a large enough sample size has its benefits.
> 
> We have hit 3 out of the 4 warnings below.
> 
> The only one we did not hit is the cfs_rq->avg_load != avg_load
> warning.

Fair enough, that one really isn't hard.

> Most of the time we seem to hit the warnings from the
> code that removes tasks from the runqueue, 

*blink*..

> but we are
> occasionally seeing it when adding tasks to the runqueue,
> as well.

OK, let me try and get my head around that.