On Tue 15-10-19 14:07:17, David Hildenbrand wrote:

Uninitialized memmaps contain garbage and in the worst case trigger kernel BUGs, especially with CONFIG_PAGE_POISONING. They should not get touched.

Let's make sure that we only consider online memory (managed by the buddy) that has initialized memmaps. ZONE_DEVICE is not applicable.

page_zone() will call page_to_nid(), which will trigger VM_BUG_ON_PGFLAGS(PagePoisoned(page), page) with CONFIG_PAGE_POISONING and CONFIG_DEBUG_VM_PGFLAGS when called on uninitialized memmaps. This can be the case when an offline memory block (e.g., never onlined) is spanned by a zone.

Note: As explained by Michal in [1], alloc_contig_range() will verify the range. So it boils down to the wrong access in this function.

[1] http://lkml.kernel.org/r/20180423000943.GO17484@dhcp22.suse.cz

Reported-by: Michal Hocko mhocko@kernel.org Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319 Cc: stable@vger.kernel.org # v4.13+ Cc: Anshuman Khandual anshuman.khandual@arm.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Andrew Morton akpm@linux-foundation.org Cc: Michal Hocko mhocko@kernel.org Signed-off-by: David Hildenbrand david@redhat.com

Acked-by: Michal Hocko mhocko@suse.com

Thanks!

---

mm/hugetlb.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c index ef37c85423a5..b45a95363a84 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1084,11 +1084,10 @@ static bool pfn_range_valid_gigantic(struct zone *z, struct page *page; for (i = start_pfn; i < end_pfn; i++) {

• if (!pfn_valid(i))
  

• page = pfn_to_online_page(i);
  

• if (!page)
  return false;
  

• page = pfn_to_page(i);
  

• if (page_zone(page) != z) return false;

2.21.0