commit 656d571193262a11c2daa4012e53e4d645bbce56 upstream.

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@redhat.com Fixes: 00d6c019b5bc ("mm/memory_hotplug: don't access uninitialized memmaps in shrink_pgdat_span()") Signed-off-by: David Hildenbrand david@redhat.com Cc: Michal Hocko mhocko@suse.com Cc: Oscar Salvador osalvador@suse.de Cc: Stephen Rothwell sfr@canb.auug.org.au Cc: Dan Williams dan.j.williams@intel.com Cc: Pavel Tatashin pasha.tatashin@soleen.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org --- mm/memory_hotplug.c | 8 ++++++++ 1 file changed, 8 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 619b81383e1f..7965112eb063 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -448,6 +448,14 @@ static void update_pgdat_span(struct pglist_data *pgdat) 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)