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

Alan Cox
2003-02-26T12:27:43Z

On Wed, 2003-02-26 at 10:28, Andrew Morton wrote:
> Dave Jones <davej@codemonkey.org.uk> 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