Re: smp_call_function_single lockups

From: Ingo Molnar
Date: Fri Feb 20 2015 - 15:11:32 EST

* Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:

> 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,

Ah, ok! Then the patch looks good to me.

( Originally we didn't wait for the ICR bit either, but
then it was added due to later erratas and was eventually
made an architectural requirement. )

> 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".



To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at