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Offlining a zone's last block > rebuilds the zonelists in place, and the shrunk list's NULL terminator > can land on the preferred slot mid-walk: > > CPU 0 CPU 1 > get_page_from_freelist(GFP_KERNEL | __GFP_THISNODE) > zone =3D NORMAL (slot 1) > offline_pages() > build_all_zonelists() > [MOVABLE, NORMAL, NULL] > -> [NORMAL, NULL] > rmqueue(zonelist_zone(slot 1), zone) > zone_statistics(NULL, zone) > > BUG: kernel NULL pointer dereference, address: 0000000000000060 > RIP: 0010:get_page_from_freelist+0x6a5/0x15f0 > Call Trace: > __alloc_frozen_pages_noprof+0x125/0x330 > > Read the slot once. Zones are never freed, so a stale zone is safe, and > a NULL slot fails the same way as walking off the end. > > Fixes: 11cd8638c37f ("mm, page_alloc: remove stop_machine from build_all_= zonelists") > Cc: stable@vger.kernel.org > Signed-off-by: Gregory Price (Meta) > Reviewed-by: Vlastimil Babka (SUSE) > --- > mm/page_alloc.c | 31 +++++++++++++++++++++++-------- > 1 file changed, 23 insertions(+), 8 deletions(-) > Makes sense. Acked-by: Zi Yan --=20 Best Regards, Yan, Zi