io_uring_wait_cqe not blocking code execution

[Nazar2]

simple tcp server to accept user connections. below is simplified code:

// create address
struct sockaddr_in address;
address.sin_family = AF_INET;
address.sin_addr.s_addr = INADDR_ANY;
address.sin_port = htons(port);

// create socket, bind, listen
int serverSocket = socket(AF_INET, SOCK_STREAM, 0);
setsockopt(serverSocket, SOL_SOCKET, SO_REUSEADDR, &opt, sizeof(opt));
setsockopt(serverSocket, IPPROTO_TCP, TCP_NODELAY, &opt, sizeof(opt));
setsockopt(serverSocket, IPPROTO_TCP, TCP_QUICKACK, &opt, sizeof(opt));
bind(serverSocket, (struct sockaddr*)&address, sizeof(address));
listen(serverSocket, SOMAXCONN);

// init io_uring
io_uring_queue_init(QUEUE_DEPTH, &ring, 0);

// submit accept
struct io_uring_sqe *sqe = io_uring_get_sqe(ring);
io_uring_prep_accept(sqe, serverSocket, (struct sockaddr *) req->clientAddr, &len, 0);
io_uring_sqe_set_data(sqe, req); // if needed some custom user data
io_uring_submit(ring);

// wait for client connection
struct io_uring_cqe * cqe;
io_uring_wait_cqe(&ring, &cqe); // should block until there is new event in completion queue event
printf("got new client\n"); // this code executes immediately without waiting for client connection in previous line
// cqe->res value is -22

io_uring_cqe_seen(&ring, cqe);

// cleanup
close(serverSocket);
io_uring_queue_exit(&ring);

is there anything wrong with the code? or it's ok and io_uring_wait_cqe should block? already tried without TCP_NODELAY and TCP_QUICKACK but it didn't helped.

[noteflakes]

You're getting -EINVAL, so you need to check the arguments you're passing to io_uring_prep_accept. From the accept(2) man page: Socket is not listening for connections, or addrlen is invalid (e.g., is negative). You're not doing any error checking on syscalls done before.

[Nazar2]

same code works on freshly installed Debian as expected and io_uring_wait_cqe is blocking :( wtf, it seems some settings in Linux should be made

[axboe]

same code works on freshly installed Debian as expected and io_uring_wait_cqe is blocking :( wtf, it seems some settings in Linux should be made

You would get that error on an older kernel that doesn't support the accept operation as well. Your original install is most likely too outdated to support accept over io_uring - what does uname -a say on both installs?

[Nazar2]

on first machine (Ubuntu with problem): Linux 5.4.0-97-generic #110-Ubuntu SMP Thu Jan 13 18:22:13 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux

on second machine (Debian no problem) I've just uninstalled it because I use it via VirtualBox and now I bought VPS and trying to set it up

[axboe]

5.4 is way too old, that's why it fails.

[axboe]

Closing this one up, not a liburing or io_uring issue, base is just too old to support accept.

[Nazar2]

thank you for quick reply