Index: example/io/attach-block.c
===================================================================
--- example/io/attach-block.c	(revision 5869cea3d27c1f6c01a80f191c1c078f5385adcb)
+++ example/io/attach-block.c	(revision 5869cea3d27c1f6c01a80f191c1c078f5385adcb)
@@ -0,0 +1,108 @@
+/*
+This is an example that uses io_uring with attach mode.
+It demonstrates the what happens if some thread submits to
+the original ring and then spins, while a second thread waits
+on the attached ring. This deadlocks because even if rings are
+attached, they don't share a completion queue. Therefore all
+completion queues must be polled for progress to be made.
+
+It uses liburing for simplicity.
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include <pthread.h>
+#include <liburing.h>
+
+volatile bool done = false;
+
+void * submitter(void * arg) {
+	struct io_uring * ring = (struct io_uring *)arg;
+
+	const char * path = __FILE__;
+
+	int fd = open(path, 0, O_RDONLY);
+	if( fd < 0) {
+		fprintf(stderr, "Can't open file: (%d) %s\n", errno, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+	printf("Opened file: %d\n", fd);
+
+	char buffer[1024];
+	struct io_uring_sqe * sqe = io_uring_get_sqe(ring);
+	io_uring_prep_read(sqe, fd, buffer, 1024, 0);
+	io_uring_submit(ring);
+
+	printf("Submitted read\n");
+
+	printf("Spinning\n");
+	while(!__atomic_load_n(&done, __ATOMIC_SEQ_CST));
+
+	return NULL;
+}
+
+void * poller(void * arg) {
+	struct io_uring * ring = (struct io_uring *)arg;
+	struct io_uring_cqe *cqe;
+
+	printf("Waiting for results\n");
+
+	int ret = io_uring_wait_cqe(ring, &cqe);
+	if( ret < 0) {
+		fprintf(stderr, "ioring wait failed: (%d) %s\n", -ret, strerror(-ret));
+		exit(EXIT_FAILURE);
+	}
+	io_uring_cqe_seen(ring, cqe);
+
+	printf("Got result\n");
+
+	__atomic_store_n(&done, true, __ATOMIC_SEQ_CST);
+	return NULL;
+}
+
+int main() {
+	struct io_uring base_ring;
+	io_uring_queue_init(8, &base_ring, 0);
+	printf("Created first ring: %d\n", base_ring.ring_fd);
+
+	struct io_uring attached_ring;
+	struct io_uring_params par;
+	memset(&par, '\0', sizeof(struct io_uring_params));
+	par.flags |= IORING_SETUP_ATTACH_WQ;
+	par.wq_fd = base_ring.ring_fd;
+	io_uring_queue_init_params(8, &attached_ring, &par);
+	printf("Attached second ring: %d\n", attached_ring.ring_fd);
+
+	printf("Forking\n");
+	pthread_t s, p;
+
+	int ret = pthread_create(&s, NULL, submitter, &base_ring);
+	if( ret < 0) {
+		fprintf(stderr, "pthread create 1 error: (%d) %s\n", errno, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	ret = pthread_create(&p, NULL, poller, &attached_ring);
+	if( ret < 0) {
+		fprintf(stderr, "pthread create 2 error: (%d) %s\n", errno, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	ret = pthread_join(p, NULL);
+	if( ret < 0) {
+		fprintf(stderr, "pthread join 2 error: (%d) %s\n", errno, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+
+	ret = pthread_join(s, NULL);
+	if( ret < 0) {
+		fprintf(stderr, "pthread join 1 error: (%d) %s\n", errno, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+}