Re: [PATCH RFC] io_uring: remove retries from io_wq_submit_work()

[Jens Axboe <axboe@kernel.dk>]

On 2/24/20 8:40 AM, Pavel Begunkov wrote:
> On 24/02/2020 18:27, Jens Axboe wrote:
>> On 2/24/20 2:15 AM, Pavel Begunkov wrote:
>>> It seems no opcode may return -EAGAIN for non-blocking case and expect
>>> to be reissued. Remove retry code from io_wq_submit_work().
>>
>> There's actually a comment right there on how that's possible :-)
> 
> Yeah, I saw it and understand the motive, and how it may happen, but can't
> find a line, which can actually return -EAGAIN. Could you please point to an
> example?

Just give it a whirl, should be easy to reproduce if you just do:

# echo 2 > /sys/block/nvme0n1/queue/nr_requests
# fio/t/io_uring /dev/nvme0n1

or something like that. It's propagated from the kiocb endio handler,
through, req->result at the bottom of io_issue_sqe()

	if (ctx->flags & IORING_SETUP_IOPOLL) {
		const bool in_async = io_wq_current_is_worker();

		if (req->result == -EAGAIN)                                     
			return -EAGAIN;
	[...]


-- 
Jens Axboe