Re: smp_call_function_single lockups

[Linus Torvalds]

On Fri, Feb 20, 2015 at 11:41 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
> I'm not so sure about that aspect: I think disabling IRQs
> might be necessary with some APICs (if lower levels don't
> disable IRQs), to make sure the 'local APIC busy' bit isn't
> set:

Right. But afaik not for the x2apic case, which this is.  The x2apic
doesn't even have a busy bit, and sending the ipi is a single write,

I agree that when doing other apic implementations, we may need to
guarantee atomicity for things like "wait for apic idle, then send the
ipi".

                        Linus
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