Re: [RFC PATCH] ARM: smp: Fix the CPU hotplug race with scheduler.

[Santosh Shilimkar]

On 6/20/2011 3:20 PM, Russell King - ARM Linux wrote:
> On Mon, Jun 20, 2011 at 02:53:59PM +0530, Santosh Shilimkar wrote:
> > The current ARM CPU hotplug code suffers from couple of race conditions
> > in CPU online path with scheduler.
> > The ARM CPU hotplug code doesn't wait for hot-plugged CPU to be marked
> > active as part of cpu_notify() by the CPU which brought it up before
> > enabling interrupts.
>
> Hmm, why not just move the set_cpu_online() call before notify_cpu_starting()
> and add the wait after the set_cpu_online() ?
I think that's what patch is doing. Do you mean, calling hotplug
notifier chain immediately after CPU marked as online. Something
like below.

	set_cpu_online(cpu, true);
	notify_cpu_starting(cpu);
        while (!cpumask_test_cpu(smp_processor_id(), cpu_active_mask))
                cpu_relax();

        /*
         * Enable local interrupts.
         */
                local_irq_enable();
        local_fiq_enable();


Regards
Santosh

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