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Message-ID: <6a10ec48-3940-cd8d-5e34-b9ade9f87b82@gmail.com>
Date: Mon, 29 May 2023 08:50:51 +0700
From: Bagas Sanjaya <bagasdotme@...il.com>
To: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linux Regressions <regressions@...ts.linux.dev>,
Linux x86 <x86@...nel.org>
Cc: David Woodhouse <dwmw@...zon.co.uk>,
Thomas Gleixner <tglx@...utronix.de>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Michael Kelley <mikelley@...rosoft.com>,
Oleksandr Natalenko <oleksandr@...alenko.name>,
Helge Deller <deller@....de>,
"Guilherme G. Piccoli" <gpiccoli@...lia.com>,
Vincent Donnefort <vdonnefort@...gle.com>,
Bert Karwatzki <spasswolf@....de>
Subject: Fwd: kernel/cpu.c: linux misses the initialization of one CPU
(off-by-one regression)
Hi,
I notice a regression report on Bugzilla [1]. Quoting from it:
> Since commit 18415f33e2ac4ab382cbca8b5ff82a9036b5bd49 linux misses the initialization of 1 CPU when the CONFIG_NR_CPUS is equal to the actual number of CPUs in the system. One can work around the issue by increasing CONFIG_NR_CPUS or apply the following patch:
>
> From aa5ef661936655f0d806fdbf2d28fc9513dd5c69 Mon Sep 17 00:00:00 2001
> From: Bert Karwatzki <spasswolf@....de>
> Date: Sun, 28 May 2023 14:35:45 +0200
> Subject: [PATCH] Fix CPU detection when CONFIG_NR_CPUS is equal to the actual
> number of CPUs.
>
> Signed-off-by: Bert Karwatzki <spasswolf@....de>
> ---
> kernel/cpu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 005f863a3d2b..5e900b531827 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1770,7 +1770,7 @@ static void __init cpuhp_bringup_mask(const struct cpumask *mask, unsigned int n
> for_each_cpu(cpu, mask) {
> struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
>
> - if (!--ncpus)
> + if (!ncpus--)
> break;
>
> if (cpu_up(cpu, target) && can_rollback_cpu(st)) {
> --
> 2.40.1
Anyway, I'm adding it to regzbot:
#regzbot introduced: 18415f33e2ac4a https://bugzilla.kernel.org/show_bug.cgi?id=217498
#regzbot title: Off-by-one CPU initalization when CONFIG_NR_CPUS equal to actual system CPU count
Thanks.
[1]: https://bugzilla.kernel.org/show_bug.cgi?id=217498
--
An old man doll... just what I always wanted! - Clara
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