On Fri, Jan 15, 2021 at 08:49:41PM +0800, Muchun Song wrote:

There is a race between isolate_huge_page() and __free_huge_page().

CPU0:                                       CPU1:

if (PageHuge(page))
                                            put_page(page)
                                              __free_huge_page(page)
                                                  spin_lock(&hugetlb_lock)
                                                  update_and_free_page(page)
                                                    set_compound_page_dtor(page,
                                                      NULL_COMPOUND_DTOR)
                                                  spin_unlock(&hugetlb_lock)
  isolate_huge_page(page)
    // trigger BUG_ON
    VM_BUG_ON_PAGE(!PageHead(page), page)
    spin_lock(&hugetlb_lock)
    page_huge_active(page)
      // trigger BUG_ON
      VM_BUG_ON_PAGE(!PageHuge(page), page)
    spin_unlock(&hugetlb_lock)

When we isolate a HugeTLB page on CPU0. Meanwhile, we free it to the
buddy allocator on CPU1. Then, we can trigger a BUG_ON on CPU0. Because
it is already freed to the buddy allocator.

Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
Signed-off-by: Muchun Song <redacted>
Reviewed-by: Mike Kravetz <redacted>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: stable@vger.kernel.org

Reviewed-by: Oscar Salvador <osalvador@suse.de>

-- 
Oscar Salvador
SUSE L3