Does need memory barrier to synchronize req->result with req->iopoll_completed

[Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>]

hi,

I have taken some further thoughts about previous IPOLL race fix patch,
if io_complete_rw_iopoll() is called in interrupt context, "req->result = res"
and "WRITE_ONCE(req->iopoll_completed, 1);" are independent store operations.
So in io_do_iopoll(), if iopoll_completed is ture, can we make sure that
req->result has already been perceived by the cpu executing io_do_iopoll()?

Regards,
Xiaoguang Wang