hugetlb: fix memoryleak in hugetlb_mcopy_atomic_pte

When alloc_huge_page fails, *pagep is set to NULL without put_page first.
So the hugepage indicated by *pagep is leaked.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 8cc5fcb ("mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY")
Signed-off-by: Miaohe Lin <[email protected]>
Acked-by: Muchun Song <[email protected]>
Reviewed-by: Anshuman Khandual <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Reviewed-by: Mike Kravetz <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: MiaoheLin

mm/hugetlb.c

@@ -5952,6 +5952,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 
 		page = alloc_huge_page(dst_vma, dst_addr, 0);
 		if (IS_ERR(page)) {
+			put_page(*pagep);
 			ret = -ENOMEM;
 			*pagep = NULL;
 			goto out;