Re: [RFC PATCH v3 1/4] virtio/vsock: don't use skbuff state to account credit

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On Thu, Mar 09, 2023 at 01:11:46PM +0300, Arseniy Krasnov wrote:
This replaces use of skbuff state to calculate new 'rx_bytes'/'fwd_cnt'
values with explicit value as input argument. This makes code more
simple, because it is not needed to change skbuff state before each
call to update 'rx_bytes'/'fwd_cnt'.

I think we should also describe the issues you found that we are fixinig
now, for example the wrong calculation in virtio_transport_dec_rx_pkt().

Something like this:

  `skb->len` can vary when we partially read the data, this complicates
  the calculation of credit to be updated in
  virtio_transport_inc_rx_pkt()/virtio_transport_dec_rx_pkt().

  Also in virtio_transport_dec_rx_pkt() we were miscalculating the
  credit since `skb->len` was redundant.

  For these reasons, let's replace the use ...
  (continue with what is written in this commit message)

And we should add the Fixes tag:

Fixes: 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")


Signed-off-by: Arseniy Krasnov <AVKrasnov@xxxxxxxxxxxxxx>
---
net/vmw_vsock/virtio_transport_common.c | 23 +++++++++++------------
1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index a1581c77cf84..618680fd9906 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -241,21 +241,18 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
}

static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
-					struct sk_buff *skb)
+					u32 len)
{
-	if (vvs->rx_bytes + skb->len > vvs->buf_alloc)
+	if (vvs->rx_bytes + len > vvs->buf_alloc)
		return false;

-	vvs->rx_bytes += skb->len;
+	vvs->rx_bytes += len;
	return true;
}

static void virtio_transport_dec_rx_pkt(struct virtio_vsock_sock *vvs,
-					struct sk_buff *skb)
+					u32 len)
{
-	int len;
-
-	len = skb_headroom(skb) - sizeof(struct virtio_vsock_hdr) - skb->len;
	vvs->rx_bytes -= len;
	vvs->fwd_cnt += len;
}
@@ -388,7 +385,9 @@ virtio_transport_stream_do_dequeue(struct vsock_sock *vsk,
		skb_pull(skb, bytes);

		if (skb->len == 0) {
-			virtio_transport_dec_rx_pkt(vvs, skb);
+			u32 pkt_len = le32_to_cpu(virtio_vsock_hdr(skb)->len);

Good catch! In my proposal I used `bytes` wrongly!

The rest LGTM!

Stefano

+
+			virtio_transport_dec_rx_pkt(vvs, pkt_len);
			consume_skb(skb);
		} else {
			__skb_queue_head(&vvs->rx_queue, skb);
@@ -437,17 +436,17 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,

	while (!msg_ready) {
		struct virtio_vsock_hdr *hdr;
+		size_t pkt_len;

		skb = __skb_dequeue(&vvs->rx_queue);
		if (!skb)
			break;
		hdr = virtio_vsock_hdr(skb);
+		pkt_len = (size_t)le32_to_cpu(hdr->len);

		if (dequeued_len >= 0) {
-			size_t pkt_len;
			size_t bytes_to_copy;

-			pkt_len = (size_t)le32_to_cpu(hdr->len);
			bytes_to_copy = min(user_buf_len, pkt_len);

			if (bytes_to_copy) {
@@ -484,7 +483,7 @@ static int virtio_transport_seqpacket_do_dequeue(struct vsock_sock *vsk,
				msg->msg_flags |= MSG_EOR;
		}

-		virtio_transport_dec_rx_pkt(vvs, skb);
+		virtio_transport_dec_rx_pkt(vvs, pkt_len);
		kfree_skb(skb);
	}

@@ -1040,7 +1039,7 @@ virtio_transport_recv_enqueue(struct vsock_sock *vsk,

	spin_lock_bh(&vvs->rx_lock);

-	can_enqueue = virtio_transport_inc_rx_pkt(vvs, skb);
+	can_enqueue = virtio_transport_inc_rx_pkt(vvs, len);
	if (!can_enqueue) {
		free_pkt = true;
		goto out;
--
2.25.1


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