So if removing O_NONBLOCK in wineserver really helps here and if there is a more or less nice way to avoid setting the flag on regular files in wineserver maybe that's a valid change?
Agreed, and I think a crucial point you've helped me see is that removing `O_NONBLOCK` will *only* affect 9p (based on my census of the `linux/fs/` tree)...which is currently broken anyway, so there shouldn't be any risk.
Tomorrow I'll close this MR and open a fresh one.