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

[Jan Beulich <jbeulich@suse.com>]

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.

--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1339,6 +1339,10 @@ int __init_memblock memblock_set_node(ph
 	int start_rgn, end_rgn;
 	int i, ret;
 
+	if (WARN_ONCE(nid == MAX_NUMNODES,
+		      "Usage of MAX_NUMNODES is deprecated. Use NUMA_NO_NODE instead\n"))
+		nid = NUMA_NO_NODE;
+
 	ret = memblock_isolate_range(type, base, size, &start_rgn, &end_rgn);
 	if (ret)
 		return ret;