It'll probably give up after some seconds trying and unmount the directory, this behavior should be default, because making the whole system unresponsive due to I/O delays is not something that makes sense.
That being said and just as I was typing the above, I just remembered that the machine where I had this particular issue uses a realtime kernel. Why you might ask, I dunno, ask those mongoloids from Debian as to why Wireguard requires rt Linux rather than just shipping Wireguard with the regular kernel.
