add test case for 5.4 io merge regression logic

Prior to switching io-wq we try to merge adjacent read/write requests.
But because of bug in merge logic io may stuck

test/462ef1f514d3-test.c

@@ -0,0 +1,90 @@
+/* SPDX-License-Identifier: MIT */
+/*
+ * Regression test for incorrect async_list io_should_merge() logic
+ * Bug was fixed in 5.5 by (commit: 561fb04 io_uring: replace workqueue usage with io-wq")
+ * Affects 5.4 lts branch, at least 5.4.106 is affected.
+ */
+#include <stdio.h>
+#include <errno.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <assert.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+#include "liburing.h"
+#include "liburing.h"
+
+
+int main(int argc, char *argv[])
+{
+	struct io_uring_sqe *sqe;
+	struct io_uring_cqe *cqe;
+	struct io_uring ring;
+	int ret, fd, pipe1[2];
+	char buf[4096];
+	struct iovec vec = {
+		.iov_base = buf,
+		.iov_len = sizeof(buf)
+	};
+	struct __kernel_timespec ts = {.tv_sec = 3, .tv_nsec = 0};
+
+	ret = pipe(pipe1);
+	assert(!ret);
+
+	fd = open("testfile", O_RDWR | O_CREAT, 0644);
+	assert(ret>=0);
+	ret = ftruncate(fd, 4096);
+	assert(!ret);
+
+	ret = io_uring_queue_init(4, &ring, 0);
+	assert(!ret);
+
+	sqe = io_uring_get_sqe(&ring);
+	io_uring_prep_readv(sqe, pipe1[0], &vec, 1, 0);
+	sqe->user_data = 1;
+
+	sqe = io_uring_get_sqe(&ring);
+	io_uring_prep_readv(sqe, fd, &vec, 1, 4096);
+	sqe->user_data = 2;
+
+	ret = io_uring_submit(&ring);
+	assert(ret == 2);
+
+	ret = io_uring_wait_cqe(&ring, &cqe);
+	assert(!ret);
+	assert(cqe->res == 0);
+	assert(cqe->user_data == 2);
+	io_uring_cqe_seen(&ring, cqe);
+
+	/*
+	 * Prepare request adjusent to previous one, so merge logic may want to
+	 * link it previous request, but because of a bug in merge logic
+	 * it may be merged with pipe-read request
+	 */
+	sqe = io_uring_get_sqe(&ring);
+	io_uring_prep_readv(sqe, fd, &vec, 1, 2048);
+	sqe->user_data = 3;
+
+	ret = io_uring_submit(&ring);
+	assert(ret == 1);
+
+	/*
+	 * Read may stuck because of because a bug there request was incorrecly
+	 * merged with pipe-read request
+	 */
+	ret = io_uring_wait_cqe_timeout(&ring, &cqe, &ts);
+	if (ret == -ETIME) {
+		printf("TEST_FAIL: readv request stuck\n");
+		return 1;
+	}
+	assert(!ret);
+
+	assert(cqe->res == 2048);
+	assert(cqe->user_data == 3);
+
+	io_uring_cqe_seen(&ring, cqe);
+	io_uring_queue_exit(&ring);
+
+	return 0;
+}

test/Makefile

@@ -17,6 +17,7 @@ test_targets += \
 	232c93d07b74-test \
 	35fa71a030ca-test \
 	500f9fbadef8-test \
+	462ef1f514d3-test \
 	7ad0e4b2f83c-test \
 	8a9973408177-test \
 	917257daa0fe-test \
@@ -150,6 +151,7 @@ test_srcs := \
 	helpers.c \
 	232c93d07b74-test.c \
 	35fa71a030ca-test.c \
+	462ef1f514d3-test.c \
 	500f9fbadef8-test.c \
 	7ad0e4b2f83c-test.c \
 	8a9973408177-test.c \