linux-kernel - Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO

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Message-ID: <20190924074751.GB23050@dhcp22.suse.cz>
Date:   Tue, 24 Sep 2019 09:47:51 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Yunsheng Lin <linyunsheng@...wei.com>, catalin.marinas@....com,
        will@...nel.org, mingo@...hat.com, bp@...en8.de, rth@...ddle.net,
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Subject: Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO_NODE aware

On Mon 23-09-19 22:34:10, Peter Zijlstra wrote:
> On Mon, Sep 23, 2019 at 06:52:35PM +0200, Michal Hocko wrote:
[...]
> > I even the
> > ACPI standard is considering this optional. Yunsheng Lin has referred to
> > the specific part of the standard in one of the earlier discussions.
> > Trying to guess the node affinity is worse than providing all CPUs IMHO.
> 
> I'm saying the ACPI standard is wrong.

Even if you were right on this the reality is that a HW is likely to
follow that standard and we cannot rule out NUMA_NO_NODE being
specified. As of now we would access beyond the defined array and that
is clearly a bug.

Let's assume that this is really a bug for a moment. What are you going
to do about that? BUG_ON? I do not really see any solution besides to either
provide something sensible or BUG_ON. If you are worried about a
conditional then this should be pretty easy to solve by starting the
array at -1 index and associate it with the online cpu mask.
-- 
Michal Hocko
SUSE Labs