Re: io_uring file descriptor address already in use error

[Jens Axboe <axboe@kernel.dk>]

On 8/25/20 9:12 AM, Jens Axboe wrote:
> On 8/25/20 9:00 AM, Josef wrote:
>> Hi,
>>
>> I found a bug submitting a server socket poll in io_uring. The file
>> descriptor is not really closed when calling close(2), if I bind a new
>> socket with the same address & port I'll get an "Already in use" error
>> message
>>
>> example to reproduce it
>> https://gist.github.com/1Jo1/3ace601884b86f7495fd5241190494dc
> 
> Not sure this is an actual bug, but depends on how you look at it. Your
> poll command has a reference to the file, which means that when you close
> it here:
> 
>     assert(close(sock_listen_fd1) == 0); 
> 
> then that's not the final close. If you move the io_uring_queue_exit()
> before that last create_server_socket() it should work, since the poll
> will have been canceled (and hence the file closed) at that point.
> 
> That said, I don't believe we actually need the file after arming the
> poll, so we could potentially close it once we've armed it. That would
> make your example work.

Actually we do need the file, in case we're re-arming poll. But as stated
in the above email, this isn't unexpected behavior. You could cancel the
poll before trying to setup the new server socket, that'd close it as
well. Then the close() would actually close it. Ordering of the two
operations wouldn't matter.

-- 
Jens Axboe