linux-kernel - Re: PATCH] sched: Fix sched_numa_find_nth

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Message-ID: <aLhplQVvIJqWo1ac@yury>
Date: Wed, 3 Sep 2025 12:15:17 -0400
From: Yury Norov <yury.norov@...il.com>
To: Christian Loehle <christian.loehle@....com>
Cc: Peter Zijlstra <peterz@...radead.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Mark Rutland <Mark.Rutland@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>
Subject: Re: PATCH] sched: Fix sched_numa_find_nth_cpu() if mask offline

On Wed, Sep 03, 2025 at 04:48:32PM +0100, Christian Loehle wrote:
> sched_numa_find_nth_cpu() uses a bsearch to look for the 'closest'
> CPU in sched_domains_numa_masks and given cpus mask. However they
> might not intersect if all CPUs in the cpus mask are offline. bsearch
> will return NULL in that case, bail out instead of dereferencing a
> bogus pointer.
> 
> The previous behaviour lead to this bug when using maxcpus=4 on an
> rk3399 (LLLLbb) (i.e. booting with all big CPUs offline):

Thanks! Scheduling for -rc5.