Re: bug with fastpoll accept and sqpoll + IOSQE_FIXED_FILE

[Jens Axboe <axboe@kernel.dk>]

On 2/2/21 1:34 PM, Pavel Begunkov wrote:
> On 02/02/2021 17:41, Pavel Begunkov wrote:
>> On 02/02/2021 17:24, Jens Axboe wrote:
>>> On 2/2/21 10:10 AM, Victor Stewart wrote:
>>>>> Can you send the updated test app?
>>>>
>>>> https://gist.github.com/victorstewart/98814b65ed702c33480487c05b40eb56
>>>>
>>>> same link i just updated the same gist
>>>
>>> And how are you running it?
>>
>> with SQPOLL    with    FIXED FLAG -> FAILURE: failed with error = ???
>> 	-> io_uring_wait_cqe_timeout() strangely returns -1, (-EPERM??)
> 
> Ok, _io_uring_get_cqe() is just screwed twice
> 
> TL;DR
> we enter into it with submit=0, do an iteration, which decrements it,
> then a second iteration passes submit=-1, which is returned back by
> the kernel as a result and propagated back from liburing...

Yep, that's what I came up with too. We really just need a clear way
of knowing when to break out, and when to keep going. Eg if we've
done a loop and don't end up calling the system call, then there's
no point in continuing.

-- 
Jens Axboe