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

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Message-ID: <20190924091714.GJ2369@hirez.programming.kicks-ass.net>
Date:   Tue, 24 Sep 2019 11:17:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Yunsheng Lin <linyunsheng@...wei.com>, catalin.marinas@....com,
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Subject: Re: [PATCH v6] numa: make node_to_cpumask_map() NUMA_NO_NODE aware

On Tue, Sep 24, 2019 at 09:47:51AM +0200, Michal Hocko wrote:
> 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.

Right, because the device node is wrong, so we fix _that_!

> 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.

The same thing I proposed earlier; force the device node to 0 (or any
other convenient random valid value) and issue a FW_BUG message to the
console.