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