Re: shutdown not affecting connection?

[Avi Kivity <avi@scylladb.com>]

On 2/8/20 10:20 PM, Glauber Costa wrote:
>>
>>> Perhaps you can reduce the
>>> problem to a small C reproducer?
>>>
>> That was my intended next step, yes
> s***, I didn't resist and I had to explain to my wife that no, I don't
> like io_uring more than I like her.
>
> But here it is.
>
> This is a modification of test/connect.c.
> I added a pthread comparison example that should achieve the same
> sequence of events:
> - try to sync connect
> - wait a bit
> - shutdown
>
> I added a fixed wait for pthread to make sure that shutdown is not
> called before connect.
>
> For io_uring, the shutdown is configurable with the program argument.
> This works just fine if I sleep before shutdown (as I would expect from a race).
> This hangs every time if I don't.
>
> Unless I am missing something I don't think this is the expected behavior


I think it is understandable. Since the socket is blocking uring moves 
the work to a workqueue, and the shutdown() happens before the workqueue 
has had a chance to process the connection attempt. So we'll have to 
cancel the sqe.


Jens, does the blocking connect doesn't consume a kernel thread while 
it's waiting for a connection? Or does it just set things up and move on?