Re: [patch] x86: 2.6.31-rc7 crash due to buggy flat_phys_pkg_id

From: Cyrill Gorcunov <gorcunov@gmail.com>
To: Ravikiran G Thirumalai <kiran@scalex86.org>
Cc: Ingo Molnar <mingo@elte.hu>, Yinghai Lu <yinghai@kernel.org>,
	torvalds@linux-foundation.org, linux-kernel@vger.kernel.org,
	shai@scalex86.org, Suresh Siddha <suresh.b.siddha@intel.com>
Subject: Re: [patch] x86: 2.6.31-rc7 crash due to buggy flat_phys_pkg_id
Date: Tue, 25 Aug 2009 23:40:11 +0400	[thread overview]
Message-ID: <20090825194011.GD5806@lenovo> (raw)
In-Reply-To: <20090825192055.GD6456@localdomain>

[Ravikiran G Thirumalai - Tue, Aug 25, 2009 at 12:20:55PM -0700]
| On Tue, Aug 25, 2009 at 10:31:30PM +0400, Cyrill Gorcunov wrote:
| >[Ingo Molnar - Tue, Aug 25, 2009 at 08:15:00PM +0200]
| >| 
| >
| >I'm definitely not APIC expert but since I was partially involved
| >letme turn in.
| >
| >Original commit which causes problem for vSMP seems to be due
| >to cpu_has_apic bit turned off (ie due to being manually disabled
| >or acpi table broken) so further read apic id will return plain
| >zero (we're talking about 64 bits now). So frnakly I don't understand
| >what is wrong with Ravikiran's patch. In case of apic disabled
| >initial apic value will be used anyway (which is latched but
| >actually may be changed, but it's not our case).
| >
| 
| Exactly my thinking.  I hoped the patch I posted solves both cases --
| does not depend on local apic id for the "fix crash on certain UP configs"
| case in the commit here:
| 
| http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=2759c3287de27266e06f1f4e82cbd2d65f6a044c
| 
| And fixes vsmp too.
| 
| >Or perhaps there is an issue in srat numa nodes numbering?
| >
| 
| Don't think so, local apic id has been used for for 'flat' and 'cluster'
| apic (which was used prior to 'flat') for atleast 15 major releases.
| 
| Cyrill/Yinghai, can you test and confirm if the patch attached does not
| regress the 'UP crash case' mentioned in
| commit 2759c3287de27266e06f1f4e82cbd2d65f6a044c please?
| 
| ---
| 

I would like to but I can;t. I don;t even know where were we hanging
at this crash case. I was only reading commit changelog and since
it was said about "not apic bit set" I thought about disabled apic case.

Personally I like much more quirk Yinghai posted which leaves phys id function
_bared_ and simple as it should be :)

And since it's too late before kernel release -- introducing read apic back
seems to be dangerous I suppose: there are a number of configs which could
be having side effect. At moment they are tested _with_ Yinghai patch and
only vSMP is issued. Though the problem need to be investigated more
closely. But I'm not knowing that much in this area.

	-- Cyrill