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

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Message-ID: <20250710101316.GJ1613376@noisy.programming.kicks-ass.net>
Date: Thu, 10 Jul 2025 12:13:16 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Chen, Yu C" <yu.c.chen@...el.com>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	kernel test robot <oliver.sang@...el.com>, oe-lkp@...ts.linux.dev,
	lkp@...el.com, linux-kernel@...r.kernel.org, x86@...nel.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 Thu, Jul 10, 2025 at 04:32:57PM +0800, Chen, Yu C wrote:
> 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>

Thanks; let me go stick this in a tree somewhere.