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

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Message-ID: <20250710082748.-DPO1rjO@linutronix.de>
Date: Thu, 10 Jul 2025 10:27:48 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: "Chen, Yu C" <yu.c.chen@...el.com>, 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: [PATCH] lib/smp_processor_id: Make migration check unconditional of
 SMP

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>
---
 lib/smp_processor_id.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/lib/smp_processor_id.c b/lib/smp_processor_id.c
index a2bb7738c373c..94b3f6b195388 100644
--- a/lib/smp_processor_id.c
+++ b/lib/smp_processor_id.c
@@ -22,10 +22,8 @@ unsigned int check_preemption_disabled(const char *what1, const char *what2)
 	if (is_percpu_thread())
 		goto out;
 
-#ifdef CONFIG_SMP
 	if (current->migration_disabled)
 		goto out;
-#endif
 
 	/*
 	 * It is valid to assume CPU-locality during early bootup:
-- 
2.50.0