From: Peter Zijlstra <peterz@infradead.org>
To: Huacai Chen <chenhuacai@loongson.cn>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@redhat.com>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Huacai Chen <chenhuacai@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org, Tiezhu Yang <yangtiezhu@loongson.cn>
Subject: Re: [PATCH] lib/smp_processor_id: Don't warn if there is only one CPU
Date: Wed, 11 Nov 2026 18:06:00 +0100 [thread overview]
Message-ID: <20261111170600.GS1779021@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20261111092421.3771992-1-chenhuacai@loongson.cn>
On Wed, Nov 11, 2026 at 05:24:21PM +0800, Huacai Chen wrote:
> When CONFIG_DEBUG_PREEMPT is enabled on a Non-SMP (single-core) kernel,
> calls to smp_processor_id() in preemptible contexts trigger some false
> positive "BUG: using smp_processor_id() in preemptible" warnings, which
> are harmless noise because the process always executes on CPU 0 and CPU
> migration is impossible.
The check is still valid, you don't want to have any code that uses
smp_processor_id() outside of preempt_disable(). Such code would be
invalid on SMP, even when ran on UP.
All code must be SMP ready.
Aside from that, nr_cpu_ids is the wrong number to check.
next prev parent reply other threads:[~2026-11-11 17:06 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-11 9:24 [PATCH] lib/smp_processor_id: Don't warn if there is only one CPU Huacai Chen
2026-11-11 17:06 ` Peter Zijlstra [this message]
2026-11-12 3:14 ` Huacai Chen
2026-11-12 8:13 ` Peter Zijlstra
2026-11-12 14:40 ` Steven Rostedt
2026-11-12 15:07 ` Peter Zijlstra
2026-11-13 2:06 ` Huacai Chen
2026-11-12 4:00 ` Tiezhu Yang
2026-11-12 9:24 ` sashiko-bot
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