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From:   Philipp Rumpf <prumpf@puffin.external.hp.com>
To:     Andrew Morton <andrewm@uow.edu.au>, Philipp Rumpf <prumpf@uzix.org>
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Subject: Re: modular net drivers
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On Sun, Jun 25, 2000 at 01:30:50AM +1000, Andrew Morton wrote:
> +static volatile int ice_block;
> +static spinlock_t freeze_lock = SPIN_LOCK_UNLOCKED;
> +
> +static int
> +antarctica(void *dummy)
> +{
> +	printk("start antarctica on %d\n", smp_processor_id());
> +	while (ice_block)
> +		;
> +	printk("stop antarctica on %d\n", smp_processor_id());
> +	return 0;
> +}
> +
> +static int
> +freeze_other_cpus(void)
> +{
> +	int cpu, retval;
> +
> +	if (!spin_trylock(&freeze_lock))
> +		return -EAGAIN;
> +
> +	printk("start freeze_other_cpus()\n");
> +	ice_block = 1;
> +	for (cpu = 0; cpu < smp_num_cpus - 1; cpu++) {
> +		retval = kernel_thread(antarctica, (void *)0, 0);
> +		if (retval < 0)
> +			goto out_melt;
> +	}
> +	printk("continue freeze_other_cpus()\n");
> +	return 0;
> +out_melt:
> +	ice_block = 0;
> +	spin_unlock(&freeze_lock);
> +	return retval;
> +}

You don't guarantee all the other kernel_threads have started executing.

Basically you need either an atomic_inc or a per-CPU flag somewhere.

	Philipp Rumpf