Re: [PATCH net-next v5 3/3] vsock/test: SO_RCVLOWAT + deferred credit update test

Stefano Garzarella
2023-11-30T13:36:14Z

On Thu, Nov 30, 2023 at 04:08:40PM +0300, Arseniy Krasnov wrote:
>Test which checks, that updating SO_RCVLOWAT value also sends credit
>update message. Otherwise mutual hungup may happen when receiver didn't
>send credit update and then calls 'poll()' with non default SO_RCVLOWAT
>value (e.g. waiting enough bytes to read), while sender waits for free
>space at receiver's side. Important thing is that this test relies on
>kernel's define for maximum packet size for virtio transport and this
>value is not exported to user: VIRTIO_VSOCK_MAX_PKT_BUF_SIZE (this
>define is used to control moment when to send credit update message).
>If this value or its usage will be changed in kernel - this test may
>become useless/broken.
>
>Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
>---
> Changelog:
> v1 -> v2:
> * Update commit message by removing 'This patch adds XXX' manner.
> * Update commit message by adding details about dependency for this
> test from kernel internal define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE.
> * Add comment for this dependency in 'vsock_test.c' where this define
> is duplicated.
> v2 -> v3:
> * Replace synchronization based on control TCP socket with vsock
> data socket - this is needed to allow sender transmit data only
> when new buffer size of receiver is visible to sender. Otherwise
> there is race and test fails sometimes.
> v3 -> v4:
> * Replace 'recv_buf()' to 'recv(MSG_DONTWAIT)' in last read operation
> in server part. This is needed to ensure that 'poll()' wake up us
> when number of bytes ready to read is equal to SO_RCVLOWAT value.
> v4 -> v5:
> * Use 'recv_buf(MSG_DONTWAIT)' instead of 'recv(MSG_DONTWAIT)'.
>
> tools/testing/vsock/vsock_test.c | 142 +++++++++++++++++++++++++++++++
> 1 file changed, 142 insertions(+)
>
>diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
>index 01fa816868bc..d66bc4987026 100644
>--- a/tools/testing/vsock/vsock_test.c
>+++ b/tools/testing/vsock/vsock_test.c
>@@ -1232,6 +1232,143 @@ static void test_double_bind_connect_client(const struct test_opts *opts)
> }
> }
>
>+#define RCVLOWAT_CREDIT_UPD_BUF_SIZE (1024 * 128)
>+/* This define is the same as in 'include/linux/virtio_vsock.h':
>+ * it is used to decide when to send credit update message during
>+ * reading from rx queue of a socket. Value and its usage in
>+ * kernel is important for this test.
>+ */
>+#define VIRTIO_VSOCK_MAX_PKT_BUF_SIZE (1024 * 64)
>+
>+static void test_stream_rcvlowat_def_cred_upd_client(const struct test_opts *opts)
>+{
>+ size_t buf_size;
>+ void *buf;
>+ int fd;
>+
>+ fd = vsock_stream_connect(opts->peer_cid, 1234);
>+ if (fd < 0) {
>+ perror("connect");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ /* Send 1 byte more than peer's buffer size. */
>+ buf_size = RCVLOWAT_CREDIT_UPD_BUF_SIZE + 1;
>+
>+ buf = malloc(buf_size);
>+ if (!buf) {
>+ perror("malloc");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ /* Wait until peer sets needed buffer size. */
>+ recv_byte(fd, 1, 0);
>+
>+ if (send(fd, buf, buf_size, 0) != buf_size) {
>+ perror("send failed");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ free(buf);
>+ close(fd);
>+}
>+
>+static void test_stream_rcvlowat_def_cred_upd_server(const struct test_opts *opts)
>+{
>+ size_t recv_buf_size;
>+ struct pollfd fds;
>+ size_t buf_size;
>+ void *buf;
>+ int fd;
>+
>+ fd = vsock_stream_accept(VMADDR_CID_ANY, 1234, NULL);
>+ if (fd < 0) {
>+ perror("accept");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ buf_size = RCVLOWAT_CREDIT_UPD_BUF_SIZE;
>+
>+ if (setsockopt(fd, AF_VSOCK, SO_VM_SOCKETS_BUFFER_SIZE,
>+ &buf_size, sizeof(buf_size))) {
>+ perror("setsockopt(SO_VM_SOCKETS_BUFFER_SIZE)");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ /* Send one dummy byte here, because 'setsockopt()' above also
>+ * sends special packet which tells sender to update our buffer
>+ * size. This 'send_byte()' will serialize such packet with data
>+ * reads in a loop below. Sender starts transmission only when
>+ * it receives this single byte.
>+ */
>+ send_byte(fd, 1, 0);
>+
>+ buf = malloc(buf_size);
>+ if (!buf) {
>+ perror("malloc");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ /* Wait until there will be 128KB of data in rx queue. */
>+ while (1) {
>+ ssize_t res;
>+
>+ res = recv(fd, buf, buf_size, MSG_PEEK);
>+ if (res == buf_size)
>+ break;
>+
>+ if (res <= 0) {
>+ fprintf(stderr, "unexpected 'recv()' return: %zi\n", res);
>+ exit(EXIT_FAILURE);
>+ }
>+ }
>+
>+ /* There is 128KB of data in the socket's rx queue,
>+ * dequeue first 64KB, credit update is not sent.
>+ */
>+ recv_buf_size = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
>+ recv_buf(fd, buf, recv_buf_size, 0, recv_buf_size);
>+ recv_buf_size++;
>+
>+ /* Updating SO_RCVLOWAT will send credit update. */
>+ if (setsockopt(fd, SOL_SOCKET, SO_RCVLOWAT,
>+ &recv_buf_size, sizeof(recv_buf_size))) {
>+ perror("setsockopt(SO_RCVLOWAT)");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ memset(&fds, 0, sizeof(fds));
>+ fds.fd = fd;
>+ fds.events = POLLIN | POLLRDNORM | POLLERR |
>+ POLLRDHUP | POLLHUP;
>+
>+ /* This 'poll()' will return once we receive last byte
>+ * sent by client.
>+ */
>+ if (poll(&fds, 1, -1) < 0) {
>+ perror("poll");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ if (fds.revents & POLLERR) {
>+ fprintf(stderr, "'poll()' error\n");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ if (fds.revents & (POLLIN | POLLRDNORM)) {

I would add a comment here, like this:

We expect poll to wake up only after receiving all the
bytes requested with SO_RCVLOWAT, so we don't want the
read to block waiting for more.

The rest LGTM.

Thanks,
Stefano

>+ recv_buf(fd, buf, recv_buf_size, MSG_DONTWAIT, recv_buf_size);
>+ } else {
>+ /* These flags must be set, as there is at
>+ * least 64KB of data ready to read.
>+ */
>+ fprintf(stderr, "POLLIN | POLLRDNORM expected\n");
>+ exit(EXIT_FAILURE);
>+ }
>+
>+ free(buf);
>+ close(fd);
>+}
>+
> static struct test_case test_cases[] = {
> {
> .name = "SOCK_STREAM connection reset",
>@@ -1342,6 +1479,11 @@ static struct test_case test_cases[] = {
> .run_client = test_double_bind_connect_client,
> .run_server = test_double_bind_connect_server,
> },
>+ {
>+ .name = "SOCK_STREAM virtio SO_RCVLOWAT + deferred cred update",
>+ .run_client = test_stream_rcvlowat_def_cred_upd_client,
>+ .run_server = test_stream_rcvlowat_def_cred_upd_server,
>+ },
> {},
> };
>
>--
>2.25.1
>