linux-kernel - Re: [PATCH] cpu/hotplug: disallow writing any state in atomic AP section to sysfs target

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Message-ID: <87zfjqao8l.ffs@tglx>
Date: Thu, 16 Jan 2025 14:21:14 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Koichiro Den <koichiro.den@...onical.com>, linux-kernel@...r.kernel.org
Cc: peterz@...radead.org
Subject: Re: [PATCH] cpu/hotplug: disallow writing any state in atomic AP
 section to sysfs target

On Fri, Dec 20 2024 at 23:15, Koichiro Den wrote:
> diff --git a/kernel/cpu.c b/kernel/cpu.c
> index 34f1a09349fc..c877443f5888 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -2127,6 +2127,7 @@ static struct cpuhp_step cpuhp_hp_states[] = {
>  	[CPUHP_BP_KICK_AP] = {
>  		.name			= "cpu:kick_ap",
>  		.startup.single		= cpuhp_kick_ap_alive,
> +		.cant_stop		= true,

Why? If it stops here, then no harm is done. The AP just waits for being
released. It won't change the state as that's a seperate handshake
mechanism.

>  	},
>  
>  	/*
> @@ -2192,6 +2193,7 @@ static struct cpuhp_step cpuhp_hp_states[] = {
>  	 * state for synchronsization */
>  	[CPUHP_AP_ONLINE] = {
>  		.name			= "ap:online",
> +		.cant_stop		= true,

Your change log is pretty unclear about the reason for this change.

Thanks,

        tglx