Patch "virtio/vsock: fix logic which reduces credit update messages" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    virtio/vsock: fix logic which reduces credit update messages

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     virtio-vsock-fix-logic-which-reduces-credit-update-m.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0025ab1ec3bb1770b2b44f1d9bbb283da430dbb4
Author: Arseniy Krasnov <avkrasnov@xxxxxxxxxxxxxxxxx>
Date:   Thu Dec 14 15:52:28 2023 +0300

    virtio/vsock: fix logic which reduces credit update messages
    
    [ Upstream commit 93b80887668226180ea5f5349cc728ca6dc700ab ]
    
    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@xxxxxxxxxxxxxxxxx>
    Reviewed-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
    Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 4084578b0b91..34a6d5e64ff2 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -398,6 +398,8 @@ 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;
 
@@ -439,7 +441,10 @@ 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);
 
@@ -449,9 +454,11 @@ 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;