[PATCH net-next v10 0/3] send credit update during setting SO_RCVLOWAT

[PATCH net-next v10 0/3] send credit update during setting SO_RCVLOWAT

[Arseniy Krasnov]

Hello,

                               DESCRIPTION

This patchset fixes old problem with hungup of both rx/tx sides and adds
test for it. This happens due to non-default SO_RCVLOWAT value and
deferred credit update in virtio/vsock. Link to previous old patchset:
https://lore.kernel.org/netdev/39b2e9fd-601b-189d-39a9-914e5574524c@sberdevices.ru/

Here is what happens step by step:

                                  TEST

                            INITIAL CONDITIONS

1) Vsock buffer size is 128KB.
2) Maximum packet size is also 64KB as defined in header (yes it is
   hardcoded, just to remind about that value).
3) SO_RCVLOWAT is default, e.g. 1 byte.


                                 STEPS

            SENDER                              RECEIVER
1) sends 128KB + 1 byte in a
   single buffer. 128KB will
   be sent, but for 1 byte
   sender will wait for free
   space at peer. Sender goes
   to sleep.


2)                                     reads 64KB, credit update not sent
3)                                     sets SO_RCVLOWAT to 64KB + 1
4)                                     poll() -> wait forever, there is
                                       only 64KB available to read.

So in step 4) receiver also goes to sleep, waiting for enough data or
connection shutdown message from the sender. Idea to fix it is that rx
kicks tx side to continue transmission (and may be close connection)
when rx changes number of bytes to be woken up (e.g. SO_RCVLOWAT) and
this value is bigger than number of available bytes to read.

I've added small test for this, but not sure as it uses hardcoded value
for maximum packet length, this value is defined in kernel header and
used to control deferred credit update. And as this is not available to
userspace, I can't control test parameters correctly (if one day this
define will be changed - test may become useless). 

Head for this patchset is:
https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net-next.git/commit/?id=9bab51bd662be4c3ebb18a28879981d69f3ef15a

Link to v1:
https://lore.kernel.org/netdev/20231108072004.1045669-1-avkrasnov@salutedevices.com/
Link to v2:
https://lore.kernel.org/netdev/20231119204922.2251912-1-avkrasnov@salutedevices.com/
Link to v3:
https://lore.kernel.org/netdev/20231122180510.2297075-1-avkrasnov@salutedevices.com/
Link to v4:
https://lore.kernel.org/netdev/20231129212519.2938875-1-avkrasnov@salutedevices.com/
Link to v5:
https://lore.kernel.org/netdev/20231130130840.253733-1-avkrasnov@salutedevices.com/
Link to v6:
https://lore.kernel.org/netdev/20231205064806.2851305-1-avkrasnov@salutedevices.com/
Link to v7:
https://lore.kernel.org/netdev/20231206211849.2707151-1-avkrasnov@salutedevices.com/
Link to v8:
https://lore.kernel.org/netdev/20231211211658.2904268-1-avkrasnov@salutedevices.com/
Link to v9:
https://lore.kernel.org/netdev/20231214091947.395892-1-avkrasnov@salutedevices.com/

Changelog:
v1 -> v2:
 * Patchset rebased and tested on new HEAD of net-next (see hash above).
 * New patch is added as 0001 - it removes return from SO_RCVLOWAT set
   callback in 'af_vsock.c' when transport callback is set - with that
   we can set 'sk_rcvlowat' only once in 'af_vsock.c' and in future do
   not copy-paste it to every transport. It was discussed in v1.
 * See per-patch changelog after ---.
v2 -> v3:
 * See changelog after --- in 0003 only (0001 and 0002 still same).
v3 -> v4:
 * Patchset rebased and tested on new HEAD of net-next (see hash above).
 * See per-patch changelog after ---.
v4 -> v5:
 * Change patchset tag 'RFC' -> 'net-next'.
 * See per-patch changelog after ---.
v5 -> v6:
 * New patch 0003 which sends credit update during reading bytes from
   socket.
 * See per-patch changelog after ---.
v6 -> v7:
 * Patchset rebased and tested on new HEAD of net-next (see hash above).
 * See per-patch changelog after ---.
v7 -> v8:
 * See per-patch changelog after ---.
v8 -> v9:
 * Patchset rebased and tested on new HEAD of net-next (see hash above).
 * Add 'Fixes' tag for the current 0002.
 * Reorder patches by moving two fixes first.
v9 -> v10:
 * Squash 0002 and 0003 and update commit message in result.

Arseniy Krasnov (3):
  virtio/vsock: fix logic which reduces credit update messages
  virtio/vsock: send credit update during setting SO_RCVLOWAT
  vsock/test: two tests to check credit update logic

 drivers/vhost/vsock.c                   |   1 +
 include/linux/virtio_vsock.h            |   1 +
 include/net/af_vsock.h                  |   2 +-
 net/vmw_vsock/af_vsock.c                |   9 +-
 net/vmw_vsock/hyperv_transport.c        |   4 +-
 net/vmw_vsock/virtio_transport.c        |   1 +
 net/vmw_vsock/virtio_transport_common.c |  43 +++++-
 net/vmw_vsock/vsock_loopback.c          |   1 +
 tools/testing/vsock/vsock_test.c        | 175 ++++++++++++++++++++++++
 9 files changed, 229 insertions(+), 8 deletions(-)

-- 
2.25.1

[PATCH net-next v10 1/3] virtio/vsock: fix logic which reduces credit update messages

[Arseniy Krasnov]

Add one more condition for sending credit update during dequeue from
stream socket: when number of bytes in the rx queue is smaller than
SO_RCVLOWAT value of the socket. This is actual for non-default value
of SO_RCVLOWAT (e.g. not 1) - idea is to "kick" peer to continue data
transmission, because we need at least SO_RCVLOWAT bytes in our rx
queue to wake up user for reading data (in corner case it is also
possible to stuck both tx and rx sides, this is why 'Fixes' is used).

Fixes: b89d882dc9fc ("vsock/virtio: reduce credit update messages")
Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
---
 Changelog:
 v6 -> v7:
  * Handle wrap of 'fwd_cnt'.
  * Do to send credit update when 'fwd_cnt' == 'last_fwd_cnt'.
 v7 -> v8:
  * Remove unneeded/wrong handling of wrap for 'fwd_cnt'.

 net/vmw_vsock/virtio_transport_common.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index c8e162c9d1df..7eabe5219ef7 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -557,6 +557,8 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	struct virtio_vsock_sock *vvs = vsk->trans;
 	size_t bytes, total = 0;
 	struct sk_buff *skb;
+	u32 fwd_cnt_delta;
+	bool low_rx_bytes;
 	int err = -EFAULT;
 	u32 free_space;
 
@@ -600,7 +602,10 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 		}
 	}
 
-	free_space = vvs->buf_alloc - (vvs->fwd_cnt - vvs->last_fwd_cnt);
+	fwd_cnt_delta = vvs->fwd_cnt - vvs->last_fwd_cnt;
+	free_space = vvs->buf_alloc - fwd_cnt_delta;
+	low_rx_bytes = (vvs->rx_bytes <
+			sock_rcvlowat(sk_vsock(vsk), 0, INT_MAX));
 
 	spin_unlock_bh(&vvs->rx_lock);
 
@@ -610,9 +615,11 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
 	 * too high causes extra messages. Too low causes transmitter
 	 * stalls. As stalls are in theory more expensive than extra
 	 * messages, we set the limit to a high value. TODO: experiment
-	 * with different values.
+	 * with different values. Also send credit update message when
+	 * number of bytes in rx queue is not enough to wake up reader.
 	 */
-	if (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
+	if (fwd_cnt_delta &&
+	    (free_space < VIRTIO_VSOCK_MAX_PKT_BUF_SIZE || low_rx_bytes))
 		virtio_transport_send_credit_update(vsk);
 
 	return total;
-- 
2.25.1

[PATCH net-next v10 2/3] virtio/vsock: send credit update during setting SO_RCVLOWAT

[Arseniy Krasnov]

Send credit update message when SO_RCVLOWAT is updated and it is bigger
than number of bytes in rx queue. It is needed, because 'poll()' will
wait until number of bytes in rx queue will be not smaller than
O_RCVLOWAT, so kick sender to send more data. Otherwise mutual hungup
for tx/rx is possible: sender waits for free space and receiver is
waiting data in 'poll()'.

Rename 'set_rcvlowat' callback to 'notify_set_rcvlowat' and set
'sk->sk_rcvlowat' only in one place (i.e. 'vsock_set_rcvlowat'), so the
transport doesn't need to do it.

Fixes: b89d882dc9fc ("vsock/virtio: reduce credit update messages")
Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
---
 Changelog:
 v9 -> v10:
  * This is squash of 0002 and 0003 from v9.

 drivers/vhost/vsock.c                   |  1 +
 include/linux/virtio_vsock.h            |  1 +
 include/net/af_vsock.h                  |  2 +-
 net/vmw_vsock/af_vsock.c                |  9 ++++++--
 net/vmw_vsock/hyperv_transport.c        |  4 ++--
 net/vmw_vsock/virtio_transport.c        |  1 +
 net/vmw_vsock/virtio_transport_common.c | 30 +++++++++++++++++++++++++
 net/vmw_vsock/vsock_loopback.c          |  1 +
 8 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index f75731396b7e..ec20ecff85c7 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -449,6 +449,7 @@ static struct virtio_transport vhost_transport = {
 		.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
+		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
 
 		.read_skb = virtio_transport_read_skb,
 	},
diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index ebb3ce63d64d..c82089dee0c8 100644
--- a/include/linux/virtio_vsock.h
+++ b/include/linux/virtio_vsock.h
@@ -256,4 +256,5 @@ void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit);
 void virtio_transport_deliver_tap_pkt(struct sk_buff *skb);
 int virtio_transport_purge_skbs(void *vsk, struct sk_buff_head *list);
 int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t read_actor);
+int virtio_transport_notify_set_rcvlowat(struct vsock_sock *vsk, int val);
 #endif /* _LINUX_VIRTIO_VSOCK_H */
diff --git a/include/net/af_vsock.h b/include/net/af_vsock.h
index e302c0e804d0..535701efc1e5 100644
--- a/include/net/af_vsock.h
+++ b/include/net/af_vsock.h
@@ -137,7 +137,6 @@ struct vsock_transport {
 	u64 (*stream_rcvhiwat)(struct vsock_sock *);
 	bool (*stream_is_active)(struct vsock_sock *);
 	bool (*stream_allow)(u32 cid, u32 port);
-	int (*set_rcvlowat)(struct vsock_sock *vsk, int val);
 
 	/* SEQ_PACKET. */
 	ssize_t (*seqpacket_dequeue)(struct vsock_sock *vsk, struct msghdr *msg,
@@ -168,6 +167,7 @@ struct vsock_transport {
 		struct vsock_transport_send_notify_data *);
 	/* sk_lock held by the caller */
 	void (*notify_buffer_size)(struct vsock_sock *, u64 *);
+	int (*notify_set_rcvlowat)(struct vsock_sock *vsk, int val);
 
 	/* Shutdown. */
 	int (*shutdown)(struct vsock_sock *, int);
diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index 816725af281f..54ba7316f808 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c
@@ -2264,8 +2264,13 @@ static int vsock_set_rcvlowat(struct sock *sk, int val)
 
 	transport = vsk->transport;
 
-	if (transport && transport->set_rcvlowat)
-		return transport->set_rcvlowat(vsk, val);
+	if (transport && transport->notify_set_rcvlowat) {
+		int err;
+
+		err = transport->notify_set_rcvlowat(vsk, val);
+		if (err)
+			return err;
+	}
 
 	WRITE_ONCE(sk->sk_rcvlowat, val ? : 1);
 	return 0;
diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
index 7cb1a9d2cdb4..e2157e387217 100644
--- a/net/vmw_vsock/hyperv_transport.c
+++ b/net/vmw_vsock/hyperv_transport.c
@@ -816,7 +816,7 @@ int hvs_notify_send_post_enqueue(struct vsock_sock *vsk, ssize_t written,
 }
 
 static
-int hvs_set_rcvlowat(struct vsock_sock *vsk, int val)
+int hvs_notify_set_rcvlowat(struct vsock_sock *vsk, int val)
 {
 	return -EOPNOTSUPP;
 }
@@ -856,7 +856,7 @@ static struct vsock_transport hvs_transport = {
 	.notify_send_pre_enqueue  = hvs_notify_send_pre_enqueue,
 	.notify_send_post_enqueue = hvs_notify_send_post_enqueue,
 
-	.set_rcvlowat             = hvs_set_rcvlowat
+	.notify_set_rcvlowat      = hvs_notify_set_rcvlowat
 };
 
 static bool hvs_check_transport(struct vsock_sock *vsk)
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index af5bab1acee1..f495b9e5186b 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -537,6 +537,7 @@ static struct virtio_transport virtio_transport = {
 		.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
+		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
 
 		.read_skb = virtio_transport_read_skb,
 	},
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 7eabe5219ef7..9d2305fdc65c 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -1690,6 +1690,36 @@ int virtio_transport_read_skb(struct vsock_sock *vsk, skb_read_actor_t recv_acto
 }
 EXPORT_SYMBOL_GPL(virtio_transport_read_skb);
 
+int virtio_transport_notify_set_rcvlowat(struct vsock_sock *vsk, int val)
+{
+	struct virtio_vsock_sock *vvs = vsk->trans;
+	bool send_update;
+
+	spin_lock_bh(&vvs->rx_lock);
+
+	/* If number of available bytes is less than new SO_RCVLOWAT value,
+	 * kick sender to send more data, because sender may sleep in its
+	 * 'send()' syscall waiting for enough space at our side. Also
+	 * don't send credit update when peer already knows actual value -
+	 * such transmission will be useless.
+	 */
+	send_update = (vvs->rx_bytes < val) &&
+		      (vvs->fwd_cnt != vvs->last_fwd_cnt);
+
+	spin_unlock_bh(&vvs->rx_lock);
+
+	if (send_update) {
+		int err;
+
+		err = virtio_transport_send_credit_update(vsk);
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(virtio_transport_notify_set_rcvlowat);
+
 MODULE_LICENSE("GPL v2");
 MODULE_AUTHOR("Asias He");
 MODULE_DESCRIPTION("common code for virtio vsock");
diff --git a/net/vmw_vsock/vsock_loopback.c b/net/vmw_vsock/vsock_loopback.c
index 048640167411..6dea6119f5b2 100644
--- a/net/vmw_vsock/vsock_loopback.c
+++ b/net/vmw_vsock/vsock_loopback.c
@@ -96,6 +96,7 @@ static struct virtio_transport loopback_transport = {
 		.notify_send_pre_enqueue  = virtio_transport_notify_send_pre_enqueue,
 		.notify_send_post_enqueue = virtio_transport_notify_send_post_enqueue,
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
+		.notify_set_rcvlowat      = virtio_transport_notify_set_rcvlowat,
 
 		.read_skb = virtio_transport_read_skb,
 	},
-- 
2.25.1

[PATCH net-next v10 3/3] vsock/test: two tests to check credit update logic

[Arseniy Krasnov]

Both tests are almost same, only differs in two 'if' conditions, so
implemented in a single function. Tests check, that credit update
message is sent:

1) During setting SO_RCVLOWAT value of the socket.
2) When number of 'rx_bytes' become smaller than SO_RCVLOWAT value.

Signed-off-by: Arseniy Krasnov <avkrasnov@salutedevices.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.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)'.
 v5 -> v6:
  * Add second test which checks, that credit update is sent during
    reading data from socket.
  * Update commit message.

 tools/testing/vsock/vsock_test.c | 175 +++++++++++++++++++++++++++++++
 1 file changed, 175 insertions(+)

diff --git a/tools/testing/vsock/vsock_test.c b/tools/testing/vsock/vsock_test.c
index 01fa816868bc..66246d81d654 100644
--- a/tools/testing/vsock/vsock_test.c
+++ b/tools/testing/vsock/vsock_test.c
@@ -1232,6 +1232,171 @@ 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_credit_update_test(const struct test_opts *opts,
+					   bool low_rx_bytes_test)
+{
+	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);
+	}
+
+	if (low_rx_bytes_test) {
+		/* Set new SO_RCVLOWAT here. This enables sending credit
+		 * update when number of bytes if our rx queue become <
+		 * SO_RCVLOWAT value.
+		 */
+		recv_buf_size = 1 + VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
+
+		if (setsockopt(fd, SOL_SOCKET, SO_RCVLOWAT,
+			       &recv_buf_size, sizeof(recv_buf_size))) {
+			perror("setsockopt(SO_RCVLOWAT)");
+			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 sent if 'low_rx_bytes_test' == true.
+	 * Otherwise, credit update is sent in 'if (!low_rx_bytes_test)'.
+	 */
+	recv_buf_size = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
+	recv_buf(fd, buf, recv_buf_size, 0, recv_buf_size);
+
+	if (!low_rx_bytes_test) {
+		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);
+		}
+	}
+
+	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)) {
+		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 void test_stream_cred_upd_on_low_rx_bytes(const struct test_opts *opts)
+{
+	test_stream_credit_update_test(opts, true);
+}
+
+static void test_stream_cred_upd_on_set_rcvlowat(const struct test_opts *opts)
+{
+	test_stream_credit_update_test(opts, false);
+}
+
 static struct test_case test_cases[] = {
 	{
 		.name = "SOCK_STREAM connection reset",
@@ -1342,6 +1507,16 @@ static struct test_case test_cases[] = {
 		.run_client = test_double_bind_connect_client,
 		.run_server = test_double_bind_connect_server,
 	},
+	{
+		.name = "SOCK_STREAM virtio credit update + SO_RCVLOWAT",
+		.run_client = test_stream_rcvlowat_def_cred_upd_client,
+		.run_server = test_stream_cred_upd_on_set_rcvlowat,
+	},
+	{
+		.name = "SOCK_STREAM virtio credit update + low rx_bytes",
+		.run_client = test_stream_rcvlowat_def_cred_upd_client,
+		.run_server = test_stream_cred_upd_on_low_rx_bytes,
+	},
 	{},
 };
 
-- 
2.25.1

Re: [PATCH net-next v10 0/3] send credit update during setting SO_RCVLOWAT

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by David S. Miller <davem@davemloft.net>:

On Thu, 14 Dec 2023 15:52:27 +0300 you wrote:
> Hello,
> 
>                                DESCRIPTION
> 
> This patchset fixes old problem with hungup of both rx/tx sides and adds
> test for it. This happens due to non-default SO_RCVLOWAT value and
> deferred credit update in virtio/vsock. Link to previous old patchset:
> https://lore.kernel.org/netdev/39b2e9fd-601b-189d-39a9-914e5574524c@sberdevices.ru/
> 
> [...]

Here is the summary with links:
  - [net-next,v10,1/3] virtio/vsock: fix logic which reduces credit update messages
    https://git.kernel.org/netdev/net-next/c/93b808876682
  - [net-next,v10,2/3] virtio/vsock: send credit update during setting SO_RCVLOWAT
    https://git.kernel.org/netdev/net-next/c/0fe179896811
  - [net-next,v10,3/3] vsock/test: two tests to check credit update logic
    https://git.kernel.org/netdev/net-next/c/542e893fbadc

You are awesome, thank you!
-- 
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