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Date: Wed, 8 Nov 2023 10:20:03 +0300
From: Arseniy Krasnov <avkrasnov@...utedevices.com>
To: Stefan Hajnoczi <stefanha@...hat.com>, Stefano Garzarella
	<sgarzare@...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>
CC: <kvm@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<kernel@...rdevices.ru>, <oxffffaa@...il.com>, <avkrasnov@...utedevices.com>
Subject: [RFC PATCH v1 1/2] virtio/vsock: send credit update during setting SO_RCVLOWAT

This adds sending 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 SO_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()'.

Signed-off-by: Arseniy Krasnov <avkrasnov@...utedevices.com>
---
 drivers/vhost/vsock.c                   |  2 ++
 include/linux/virtio_vsock.h            |  1 +
 net/vmw_vsock/virtio_transport.c        |  2 ++
 net/vmw_vsock/virtio_transport_common.c | 31 +++++++++++++++++++++++++
 net/vmw_vsock/vsock_loopback.c          |  2 ++
 5 files changed, 38 insertions(+)

diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index f75731396b7e..ecfa5c11f5ee 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -451,6 +451,8 @@ static struct virtio_transport vhost_transport = {
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
 
 		.read_skb = virtio_transport_read_skb,
+
+		.set_rcvlowat             = virtio_transport_set_rcvlowat
 	},
 
 	.send_pkt = vhost_transport_send_pkt,
diff --git a/include/linux/virtio_vsock.h b/include/linux/virtio_vsock.h
index ebb3ce63d64d..97dc1bebc69c 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_set_rcvlowat(struct vsock_sock *vsk, int val);
 #endif /* _LINUX_VIRTIO_VSOCK_H */
diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index af5bab1acee1..cf3431189d0c 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c
@@ -539,6 +539,8 @@ static struct virtio_transport virtio_transport = {
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
 
 		.read_skb = virtio_transport_read_skb,
+
+		.set_rcvlowat             = virtio_transport_set_rcvlowat
 	},
 
 	.send_pkt = virtio_transport_send_pkt,
diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index e22c81435ef7..88a58163046e 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -1676,6 +1676,37 @@ 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_set_rcvlowat(struct vsock_sock *vsk, int val)
+{
+	struct virtio_vsock_sock *vvs = vsk->trans;
+	bool send_update = false;
+
+	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.
+	 */
+	if (vvs->rx_bytes < val)
+		send_update = true;
+
+	spin_unlock_bh(&vvs->rx_lock);
+
+	if (send_update) {
+		int err;
+
+		err = virtio_transport_send_credit_update(vsk);
+		if (err < 0)
+			return err;
+	}
+
+	WRITE_ONCE(sk_vsock(vsk)->sk_rcvlowat, val ? : 1);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(virtio_transport_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..388c157f6633 100644
--- a/net/vmw_vsock/vsock_loopback.c
+++ b/net/vmw_vsock/vsock_loopback.c
@@ -98,6 +98,8 @@ static struct virtio_transport loopback_transport = {
 		.notify_buffer_size       = virtio_transport_notify_buffer_size,
 
 		.read_skb = virtio_transport_read_skb,
+
+		.set_rcvlowat             = virtio_transport_set_rcvlowat
 	},
 
 	.send_pkt = vsock_loopback_send_pkt,
-- 
2.25.1


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