Re: [patch 2/5] x86_64: CPU hotplug support.

[Ashok Raj <ashok.raj@intel.com>]

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.