Re: [PATCH 1/5] stack overflow safe kdump (2.6.16-rc1-i386) - safe_smp_processor_id

[ebiederm@xmission.com (Eric W. Biederman)]

Fernando Luis Vazquez Cao <fernando@intellilink.co.jp> writes:

> On Wed, 2006-01-25 at 09:07 +0100, Arjan van de Ven wrote:
>> On Tue, 2006-01-24 at 23:59 -0800, Andrew Morton wrote:
>> > Andi Kleen <ak@suse.de> wrote:
>> > >
>> > > On Wednesday 25 January 2006 08:10, Andrew Morton wrote:
>> > > 
>> > > > It assumes that all x86 SMP machines have APICs.  That's untrue of
> Voyager.
>> > > > I think we can probably live with this assumption - others would know
>> > > > better than I.
>> > > 
>> > > Early x86s didn't have APICs and they are still often disabled on not so 
>> > > old mobile CPUs.  I don't think it's a good assumption to make for i386.
>> > > 
>> > 
>> > But how many of those do SMP?
>> 
>> even on SMP boxes you regularly need to (runtime) disable apics. Several
>> boards out there just have busted apics, or at least when used with
>> linux. "noapic" is one of the more frequent things distro support people
>> tell customers over the phone....
> Checking whether ioapic_setup_disabled is set should suffice, right?
> Does the patch below look good?

Actually hard_smp_processor_id should only care about local apics.
Disabling the io_apics should have no affect, on this code path.

So I believe testing for io_apics being enabled is actively wrong.

If the local apics are disabled the feature flag should be cleared,
and we are uniprocessor anyway.

Eric