What does -EIOCBQUEUED do?

Hello.

There are several locations that handle
-EIOCBQUEUED error code.
According to include/linux/errno.h ,
it seems this code is NFS related and
caller will receive completion event later.
But I couldn't figure out where is the beginning point
and what is happening.

What functions are called before aio_complete() is called?
(For example, is udp_recvmsg() called if sock_recvmsg() for
UDP socket returned -EIOCBQUEUED?)

What memory regions are accessed before aio_complete() is called?
(For example, is "struct msghdr"->msg_name accessed
if sock_recvmsg() for UDP socket returned -EIOCBQUEUED?)

Regards.