hugetlb: before freeing hugetlb page set dtor to appropriate value

When removing a hugetlb page from the pool the ref count is set to one (as
the free page has no ref count) and compound page destructor is set to
NULL_COMPOUND_DTOR.  Since a subsequent call to free the hugetlb page will
call __free_pages for non-gigantic pages and free_gigantic_page for
gigantic pages the destructor is not used.

However, consider the following race with code taking a speculative
reference on the page:

Thread 0				Thread 1
--------				--------
remove_hugetlb_page
  set_page_refcounted(page);
  set_compound_page_dtor(page,
           NULL_COMPOUND_DTOR);
					get_page_unless_zero(page)
__update_and_free_page
  __free_pages(page,
           huge_page_order(h));

		/* Note that __free_pages() will simply drop
		   the reference to the page. */

					put_page(page)
					  __put_compound_page()
					    destroy_compound_page
					      NULL_COMPOUND_DTOR
						BUG: kernel NULL pointer
						dereference, address:
						0000000000000000

To address this race, set the dtor to the normal compound page dtor for
non-gigantic pages.  The dtor for gigantic pages does not matter as
gigantic pages are changed from a compound page to 'just a group of pages'
before freeing.  Hence, the destructor is not used.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Kravetz <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Mina Almasry <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions