Re: Polled I/O cannot find completions

[Bijan Mottahedeh <bijan.mottahedeh@oracle.com>]

>> Does io_uring though have to deal with BLK_QC_T_NONE at all?  Or are you
>> saying that it should never receive that result?
>> That's one of the things I'm not clear about.
> BLK_QC_T_* are block cookies, they are only valid in the block layer.
> Only the poll handler called should have to deal with them, inside
> their f_op->iopoll() handler. It's simply passed from the queue to
> the poll side.
>
> So no, io_uring shouldn't have to deal with them at all.
>
> The problem, as I see it, is if the block layer returns BLK_QC_T_NONE
> and the IO was actually queued and requires polling to be found. We'd
> end up with IO timeouts for handling those requests, and that's not a
> good thing...

I see requests in io_do_iopoll() on poll_list with req->res == -EAGAIN, 
I think because the completion happened after an issued request was 
added to poll_list in io_iopoll_req_issued().

How should we deal with such a request, reissue unconditionally or 
something else?

--bijan