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

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Message-ID: <Z92nQ8fQRGoEh4+k@devvm1948.rva0.facebook.com>
Date: Fri, 21 Mar 2025 10:52:29 -0700
From: Pat Cody <pat@...cody.io>
To: Christian Loehle <christian.loehle@....com>
Cc: mingo@...hat.com, peterz@...radead.org, 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, riel@...riel.com,
	patcody@...a.com, kernel-team@...a.com, stable@...r.kernel.org
Subject: Re: [PATCH] sched/fair: Add null pointer check to pick_next_entity()

On Thu, Mar 20, 2025 at 10:42:44PM +0000, Christian Loehle wrote:
> Did this happen on mainline? Any chance it's reproducible?

We have the following back-ported on top of 6.13:

sched/fair: Adhere to place_entity() constraints (not upstreamed, see https://lore.kernel.org/all/20250207111141.GD7145@noisy.programming.kicks-ass.net/)
a430d99e3490 sched/fair: Fix value reported by hot tasks pulled in /proc/schedstat
2a77e4be12cb sched/fair: Untangle NEXT_BUDDY and pick_next_task()

We don't have a repro, but the crash in pick_task_fair happens more
often than MCE crashes with our limited deployment of 6.13.