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SubjectRe: [patch 2/5] x86_64: CPU hotplug support.
On Thu, Jun 02, 2005 at 05:45:14PM -0600, Zwane Mwaikambo wrote:
> On Thu, 2 Jun 2005, Ashok Raj wrote:
>
> > > > + lock_ipi_call_lock();
> > > > cpu_set(smp_processor_id(), cpu_online_map);
> > > > mb();
> > > > + unlock_ipi_call_lock();
> > >
> > > What's that? Is this another smp_call_function race workaround? I thought
> > > there was an additional patch to avoid the broadcast.
> >
> > The other patch avoids sending to offline cpu's, but we read cpu_online_map
> > and clear self bit in smp_call_function. If a cpu comes online, dont we
> > want this cpu to take part in smp_call_function?
>
> The lock being held in smp_call_function whilst we access cpu_online_map
> should prevent another processor coming online within that operation
> shouldn't it? So There shouldn't be any processors coming online except
> for right after or before an smp_call_function.

precicely why we hold the same lock when we set the bit in cpu_online_map
during cpu_up as well.
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