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Date: Fri, 28 Jul 2006 22:15:08 -0700
From: Andrew Morton <akpm@osdl.org>
To: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: linux-kernel@vger.kernel.org, pavel@ucw.cz
Subject: Re: [PATCH -mm][resend] Disable CPU hotplug during suspend
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On Fri, 28 Jul 2006 10:15:29 +0200
"Rafael J. Wysocki" <rjw@sisk.pl> wrote:

> int disable_nonboot_cpus(void)
> +{
> +	int cpu, error = 0;
> +
> +	/* We take all of the non-boot CPUs down in one shot to avoid races
> +	 * with the userspace trying to use the CPU hotplug at the same time
> +	 */
> +	mutex_lock(&cpu_add_remove_lock);
> +	cpus_clear(frozen_cpus);
> +	printk("Disabling non-boot CPUs ...\n");
> +	for_each_online_cpu(cpu) {
> +		if (cpu == 0)
> +			continue;

This is presumably only called on cpu 0, yes?

How can we guarantee that, given that preemption is enabled?

What happens if cpu 0 isn't online?