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From:   Richard Gooch <rgooch@ras.ucalgary.ca>
To:     Philipp Rumpf <prumpf@puffin.external.hp.com>
Cc:     Andrew Morton <andrewm@uow.edu.au>,
        Philipp Rumpf <prumpf@uzix.org>,
        Rusty Russell <rusty@linuxcare.com.au>,
        Keith Owens <kaos@ocs.com.au>,
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Subject: Re: modular net drivers
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Philipp Rumpf writes:
> 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.

Or why not use smp_call_function()? Just move it from the i386 tree to
the generic tree.

				Regards,

					Richard....
Permanent: rgooch@atnf.csiro.au
Current:   rgooch@ras.ucalgary.ca