[V4 PATCH 4/4] x86/apic: Introduce noextnmi boot option

[Peter Zijlstra]

On Thu, Oct 01, 2015 at 02:33:18AM +0000, 河合英宏 / KAWAI，HIDEHIRO wrote:
> > On Fri, Sep 25, 2015 at 08:28:11PM +0900, Hidehiro Kawai wrote:
> > > This patch introduces new boot option "noextnmi" which disables
> > > external NMI.  This option is useful for the dump capture kernel
> > > so that an HA application or administrator wouldn't mistakenly
> > > shoot down the kernel by NMI.
> > 
> > So that they can get really stuck when the crash kernel crashes, right?
> > ;-)
> 
> No, it is different from my intention.
> 
> `mistakenly' in the above means; they issue NMI due to a misconception
> that the monitored host is stuck in the 1st kernel while it is actually
> taking a crash dump in the 2nd kernel.  To avoid this kind of accident,
> there is a tool such as fence_kdump which notifies "I'm taking a crash
> dump, so don't send NMI" to the HA clustering software.  However, there
> is a time window between kernel panic and the notification.
> 
> "noextnmi" allows users to avoid this kind of accident all the time of
> 2nd kernel.

Yes yes, I understand. But if the crash kernel also gets stuck they have
no means of recovery, right? (other than power cycling the hardware)

Just playing devils advocate here, I don't actually object to the patch.