Date: Thu, 30 Nov 2023 14:36:03 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: Arseniy Krasnov <avkrasnov@...utedevices.com>
Cc: Stefan Hajnoczi <stefanha@...hat.com>, 
	"David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	"Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>, 
	Bobby Eshleman <bobby.eshleman@...edance.com>, kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org, kernel@...rdevices.ru, 
	oxffffaa@...il.com
Subject: Re: [PATCH net-next v5 3/3] vsock/test: SO_RCVLOWAT + deferred
 credit update test

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@...utedevices.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
>

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