Re: [PATCH v5 04/12] mm/page_alloc: detect zonelist rebuilds from memory hot-add

["Zi Yan" <ziy@nvidia.com>]

On Sat Oct 31, 2026 at 10:13 PM EDT, Gregory Price (Meta) wrote:
> The zonelist_update_seq retry was limited to CONFIG_MEMORY_HOTREMOVE,
> presumably because only hot-remove takes zones out of a zonelist.
>
> However, build_zonerefs_node() rewrites the zonelists in place, so
> onlining the first block of a zone shifts the entries that follow it
> in every zonelist containing that zone.  This can cause a spurious
> allocation failure for a __GFP_THISNODE caller.
>
> For a node with only ZONE_NORMAL, onlining its first ZONE_MOVABLE block
> rewrites the node's ZONELIST_NOFALLBACK list as:
>
>   [NORMAL, NULL] -> [MOVABLE, NULL] -> [MOVABLE, NORMAL, NULL]
>
> A concurrent GFP_KERNEL | __GFP_THISNODE allocation can observe the
> intermediate list, skip ZONE_MOVABLE, and find no eligible zone. With
> CONFIG_MEMORY_HOTREMOVE=n, check_retry_zonelist() returns 0 and the
> allocation fails even though the node has free ZONE_NORMAL memory.
>
> Gate the sequence checks on CONFIG_MEMORY_HOTPLUG, which covers every
> configuration that rebuilds zonelists after boot.
>
> Fixes: 3d36424b3b58 ("mm/page_alloc: fix race condition between build_all_zonelists and page allocation")
> Cc: stable@vger.kernel.org
> Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
> Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
> ---
>  mm/page_alloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>

Acked-by: Zi Yan <ziy@nvidia.com>


-- 
Best Regards,
Yan, Zi