Re: [PATCH][2.5] fix preempt-issues with smp_call_function()

[Alan Cox]

On Wed, 2003-02-26 at 10:28, Andrew Morton wrote:
> Dave Jones <[e-mail]> wrote:
> >
> > btw, (unrelated) shouldn't smp_call_function be doing magick checks
> > with cpu_online() ?
> 
> Looks OK?  It sprays the IPI out to all the other CPUs in cpu_online_map,
> and waits for num_online_cpus()-1 CPUs to answer.

You cannot do that by counting without a lot of care. IPI messages do not have
guaranteed "once only" semantics. On an error a resend can and has been observed
to cause a reissue of an IPI on PII/PIII setups