Re: [PATCH] memblock: make memblock_set_node() also warn about use of MAX_NUMNODES

[Jan Beulich <jbeulich@suse.com>]

On 30.05.2024 09:48, Mike Rapoport wrote:
> On Wed, May 29, 2024 at 09:39:10AM +0200, Jan Beulich wrote:
>> On an (old) x86 system with SRAT just covering space above 4Gb:
>>
>>     ACPI: SRAT: Node 0 PXM 0 [mem 0x100000000-0xfffffffff] hotplug
>>
>> the commit referenced below leads to this NUMA configuration no longer
>> being refused by a CONFIG_NUMA=y kernel (previously
>>
>>     NUMA: nodes only cover 6144MB of your 8185MB e820 RAM. Not used.
>>     No NUMA configuration found
>>     Faking a node at [mem 0x0000000000000000-0x000000027fffffff]
>>
>> was seen in the log directly after the message quoted above), because of
>> memblock_validate_numa_coverage() checking for NUMA_NO_NODE (only). This
>> in turn led to memblock_alloc_range_nid()'s warning about MAX_NUMNODES
>> triggering, followed by a NULL deref in memmap_init() when trying to
>> access node 64's (NODE_SHIFT=6) node data.
>>
>> To compensate said change, make memblock_set_node() warn on and adjust
>> a passed in value of MAX_NUMNODES, just like various other functions
>> already do.
>>
>> Fixes: ff6c3d81f2e8 ("NUMA: optimize detection of memory with no node id assigned by firmware")
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> Cc: stable@vger.kernel.org
>> ---
>> This still leaves MAX_NUMNODES uses in various other places.
>> Interestingly
>> https://lore.kernel.org/lkml/20170309034415.GA16588@WeideMacBook-Pro.local/T/#t
>> was a more complete patch which, for an unclear reason, looks to never
>> have made it anywhere. IOW the two memblock_set_node() invocations from x86'es
>> numa_init() likely also want adjusting, among others.
> 
> They do. And I think that actually would be the right fix.
> The warning and nid adjustment in memblock can be added for robustness, but
> the calls to memblock_set_node() in x86 should be fixed regardless.

And indeed I sent one already:
https://lkml.org/lkml/2024/5/29/354

For addressing the regression either is sufficient.

Jan