Re: Lost IPIs during CPU Hotplug

From: Heiko Carstens
Date: Tue May 21 2013 - 10:52:59 EST

On Mon, May 20, 2013 at 02:37:43PM +0200, Heiko Carstens wrote:
> I just got a dump from a system running a 3.0.something kernel, however I
> think the problem exists with current kernels as well.
> Testcase was some I/O intense workload together with cpu hotplug stress.
> When trying to bring a cpu online we got an endless loop on the cpu that
> issued the cpu_up and called smp_call_function_single() within its cpu
> hotplug notifier:


> It looks to me like the IPI(s) was lost when cpu 3 was brought down before:


> So it looks to me like yet another CPU_DYING cpu hotplug notifier is needed
> for the generic smp code, which looks for pending IPIs on the to be brought
> down cpu and executes them.
> Does that make sense?

Ok, I was able to reproduce it. And the fix should be in the s390 specific
arch code within __cpu_disable() just before the cpu gets removed from the
cpu online mask.
No idea why this never has been seen before.

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