linux-kernel - Re: [PATCH] lib/smp_processor_id: Make migration check unconditional of SMP

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Message-ID: <cf437def-4542-4b73-b62b-ae9b304d40be@intel.com>
Date: Thu, 10 Jul 2025 16:32:57 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Ingo Molnar
	<mingo@...nel.org>
CC: kernel test robot <oliver.sang@...el.com>, <oe-lkp@...ts.linux.dev>,
	<lkp@...el.com>, <linux-kernel@...r.kernel.org>, <x86@...nel.org>, "Peter
 Zijlstra" <peterz@...radead.org>, Dietmar Eggemann
	<dietmar.eggemann@....com>, Juri Lelli <juri.lelli@...hat.com>, Linus
 Torvalds <torvalds@...ux-foundation.org>, Mel Gorman <mgorman@...e.de>,
	"Shrikanth Hegde" <sshegde@...ux.ibm.com>, Steven Rostedt
	<rostedt@...dmis.org>, "Valentin Schneider" <vschneid@...hat.com>, Vincent
 Guittot <vincent.guittot@...aro.org>, <aubrey.li@...ux.intel.com>
Subject: Re: [PATCH] lib/smp_processor_id: Make migration check unconditional
 of SMP

On 7/10/2025 4:27 PM, Sebastian Andrzej Siewior wrote:
> Commit cac5cefbade90 ("sched/smp: Make SMP unconditional")
> migrate_disable() even on UP builds.
> Commit 06ddd17521bf1 ("sched/smp: Always define is_percpu_thread() and
> scheduler_ipi()") made is_percpu_thread() check the affinity mask
> instead replying always true for UP mask.
> 
> As a consequence smp_processor_id() now complains if invoked within a
> migrate_disable() section because is_percpu_thread() checks its mask and
> the migration check is left out.
> 
> Make migration check unconditional of SMP.
> 
> Fixes: cac5cefbade90 ("sched/smp: Make SMP unconditional")
> Reported-by: kernel test robot <oliver.sang@...el.com>
> Closes: https://lore.kernel.org/oe-lkp/202507100448.6b88d6f1-lkp@intel.com
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
> ---

 From my understanding,

Reviewed-by: Chen Yu <yu.c.chen@...el.com>

thank you for fixing this.

best,
Chenyu