From: David Hildenbrand <david@xxxxxxxxxx> Subject: mm/memory_hotplug: fix updating the node span We recently started updating the node span based on the zone span to avoid touching uninitialized memmaps. Currently, we will always detect the node span to start at 0, meaning a node can easily span too many pages. pgdat_is_empty() will still work correctly if all zones span no pages. We should skip over all zones without spanned pages and properly handle the first detected zone that spans pages. Unfortunately, in contrast to the zone span (/proc/zoneinfo), the node span cannot easily be inspected and tested. The node span gives no real guarantees when an architecture supports memory hotplug, meaning it can easily contain holes or span pages of different nodes. The node span is not really used after init on architectures that support memory hotplug. E.g., we use it in mm/memory_hotplug.c:try_offline_node() and in mm/kmemleak.c:kmemleak_scan(). These users seem to be fine. Link: http://lkml.kernel.org/r/20191027222714.5313-1-david@xxxxxxxxxx Fixes: 00d6c019b5bc ("mm/memory_hotplug: don't access uninitialized memmaps in shrink_pgdat_span()") Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memory_hotplug.c | 8 ++++++++ 1 file changed, 8 insertions(+) --- a/mm/memory_hotplug.c~mm-memory_hotplug-fix-updating-the-node-span +++ a/mm/memory_hotplug.c @@ -447,6 +447,14 @@ static void update_pgdat_span(struct pgl zone->spanned_pages; /* No need to lock the zones, they can't change. */ + if (!zone->spanned_pages) + continue; + if (!node_end_pfn) { + node_start_pfn = zone->zone_start_pfn; + node_end_pfn = zone_end_pfn; + continue; + } + if (zone_end_pfn > node_end_pfn) node_end_pfn = zone_end_pfn; if (zone->zone_start_pfn < node_start_pfn) _
