extern ssize_t mfill_atomic_continue(struct mm_struct *dst_mm, unsigned long dst_start,
				     unsigned long len, atomic_t *mmap_changing,
				     uffd_flags_t flags)
extern ssize_t mfill_atomic_continue(struct userfaultfd_ctx *ctx, unsigned long dst_start,
				     unsigned long len, uffd_flags_t flags)