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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Hsin-Yi Wang <hsinyi@chromium.org>
Cc:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Jiri Kosina <jkosina@suse.cz>,
        Pavankumar Kondeti <pkondeti@codeaurora.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Zhenzhong Duan <zhenzhong.duan@oracle.com>,
        Aaro Koskinen <aaro.koskinen@nokia.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Guenter Roeck <groeck@chromium.org>,
        Stephen Boyd <swboyd@chromium.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC v2] reboot: hotplug cpus in migrate_to_reboot_cpu()
In-Reply-To: <20191009232655.48583-1-hsinyi@chromium.org>
Date:   Thu, 09 Jan 2020 21:15:40 +0100
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Hsin-Yi Wang <hsinyi@chromium.org> writes:

> @@ -220,8 +221,6 @@ void migrate_to_reboot_cpu(void)
>  	/* The boot cpu is always logical cpu 0 */
>  	int cpu = reboot_cpu;
>  
> -	cpu_hotplug_disable();
> -
>  	/* Make certain the cpu I'm about to reboot on is online */
>  	if (!cpu_online(cpu))
>  		cpu = cpumask_first(cpu_online_mask);
> @@ -231,6 +230,11 @@ void migrate_to_reboot_cpu(void)
>  
>  	/* Make certain I only run on the appropriate processor */
>  	set_cpus_allowed_ptr(current, cpumask_of(cpu));
> +
> +	/* Hotplug other cpus if possible */
> +#ifdef CONFIG_HOTPLUG_CPU
> +	offline_secondary_cpus(cpu);
> +#endif

In general I like the idea, but shouldn't this remove the architecture
code as a follow up?

Also this needs to be explicitely enabled per architecture (opt-in) and
not as an unconditional operation for all architectures which support
CPU hotplug.

Thanks,

        tglx