mm: migrate: fix missing update page_private to hugetlb_page_subpool

Since commit d6995da31122 ("hugetlb: use page.private for hugetlb specific
page flags") converts page.private for hugetlb specific page flags.  We
should use hugetlb_page_subpool() to get the subpool pointer instead of
page_private().

This 'could' prevent the migration of hugetlb pages.  page_private(hpage)
is now used for hugetlb page specific flags.  At migration time, the only
flag which could be set is HPageVmemmapOptimized.  This flag will only be
set if the new vmemmap reduction feature is enabled.  In addition,
!page_mapping() implies an anonymous mapping.  So, this will prevent
migration of hugetb pages in anonymous mappings if the vmemmap reduction
feature is enabled.

In addition, that if statement checked for the rare race condition of a
page being migrated while in the process of being freed.  Since that check
is now wrong, we could leak hugetlb subpool usage counts.

The commit forgot to update it in the page migration routine.  So fix it.

[[email protected]: fix compiler error when !CONFIG_HUGETLB_PAGE reported by Randy]
  Link: https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Fixes: d6995da31122 ("hugetlb: use page.private for hugetlb specific page flags")
Signed-off-by: Muchun Song <[email protected]>
Reported-by: Anshuman Khandual <[email protected]>
Reviewed-by: Mike Kravetz <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Tested-by: Anshuman Khandual <[email protected]>	[arm64]
Cc: Oscar Salvador <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Xiongchun Duan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

2 files changed, 6 insertions, 1 deletions

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index f11ba701e199..a58e11f2db15 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -898,6 +898,11 @@ static inline void huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
 #else	/* CONFIG_HUGETLB_PAGE */
 struct hstate {};
 
+static inline struct hugepage_subpool *hugetlb_page_subpool(struct page *hpage)
+{
+	return NULL;
+}
+
 static inline int isolate_or_dissolve_huge_page(struct page *page,
 						struct list_head *list)
 {
diff --git a/mm/migrate.c b/mm/migrate.c
index 8fc766e52e52..9bd6bc12aa72 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1293,7 +1293,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
 	 * page_mapping() set, hugetlbfs specific move page routine will not
 	 * be called and we could leak usage counts for subpools.
 	 */
-	if (page_private(hpage) && !page_mapping(hpage)) {
+	if (hugetlb_page_subpool(hpage) && !page_mapping(hpage)) {
 		rc = -EBUSY;
 		goto out_unlock;
 	}