linux-kernel - Re: [PATCH] x86/NUMA: don't pass MAX_NUMNODES to memblock_set

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Date: Wed, 29 May 2024 09:08:12 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Jan Beulich <jbeulich@...e.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>,
 Andrew Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/NUMA: don't pass MAX_NUMNODES to memblock_set_node()

On 5/29/24 09:00, Jan Beulich wrote:
>> In other words, it's not completely clear why ff6c3d81f2e8 introduced
>> this problem.
> It is my understanding that said change, by preventing the NUMA
> configuration from being rejected, resulted in different code paths to
> be taken. The observed crash was somewhat later than the "No NUMA
> configuration found" etc messages. Thus I don't really see a connection
> between said change not having had any MAX_NUMNODES check and it having
> introduced the (only perceived?) regression.

So your system has a bad NUMA config.  If it's rejected, then all is
merry.  Something goes and writes over the nids in all of the memblocks
to point to 0 (probably).

If it _isn't_ rejected, then it leaves a memblock in place that points
to MAX_NUMNODES.  That MAX_NUMNODES is a ticking time bomb for later.

So this patch doesn't actually revert the rejection behavior change in
the Fixes: commit.  It just makes the rest of the code more tolerant to
_not_ rejecting the NUMA config?