extern ssize_t mfill_atomic_hugetlb(struct vm_area_struct *dst_vma,
				    unsigned long dst_start,
				    unsigned long src_start,
				    unsigned long len,
				    atomic_t *mmap_changing,
				    uffd_flags_t flags)
extern ssize_t mfill_atomic_hugetlb(struct userfaultfd_ctx *ctx,
				    struct vm_area_struct *dst_vma,
				    unsigned long dst_start,
				    unsigned long src_start,
				    unsigned long len,
				    uffd_flags_t flags)