On Tue, May 05, 2026 at 07:14:36AM -0700, Eric Dumazet wrote:
On Tue, May 5, 2026 at 6:52 AM Stefano Garzarella <[email protected]> wrote:On Thu, Apr 30, 2026 at 12:26:52PM +0000, Eric Dumazet wrote: >virtio_transport_inc_rx_pkt() checks vvs->rx_bytes + len > vvs->buf_alloc. > >virtio_transport_recv_enqueue() skips coalescing for packets >with VIRTIO_VSOCK_SEQ_EOM. > >If fed with packets with len == 0 and VIRTIO_VSOCK_SEQ_EOM, >a very large number of packets can be queued >because vvs->rx_bytes stays at 0. > >Fix this by estimating the skb metadata size: > > (Number of skbs in the queue) * SKB_TRUESIZE(0) > >Fixes: 077706165717 ("virtio/vsock: don't use skbuff state to account credit") >Signed-off-by: Eric Dumazet <[email protected]> >Cc: Arseniy Krasnov <[email protected]> >Cc: Stefan Hajnoczi <[email protected]> >Cc: Stefano Garzarella <[email protected]> >Cc: "Michael S. Tsirkin" <[email protected]> >Cc: Jason Wang <[email protected]> >Cc: Xuan Zhuo <[email protected]> >Cc: "Eugenio Pérez" <[email protected]> >Cc: [email protected] >Cc: [email protected] >--- > net/vmw_vsock/virtio_transport_common.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > >diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c >index 416d533f493d7b07e9c77c43f741d28cfcd0953e..9b8014516f4fb1130ae184635fbba4dfee58bd64 100644 >--- a/net/vmw_vsock/virtio_transport_common.c >+++ b/net/vmw_vsock/virtio_transport_common.c >@@ -447,7 +447,9 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, > static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs, > u32 len) > { >- if (vvs->buf_used + len > vvs->buf_alloc) >+ u64 skb_overhead = (skb_queue_len(&vvs->rx_queue) + 1) * SKB_TRUESIZE(0); >+ >+ if (skb_overhead + vvs->buf_used + len > vvs->buf_alloc) > return false; I'm not sure about this fix, I mean that maybe this is incomplete. In virtio-vsock, there is a credit mechanism between the two peers: https://docs.oasis-open.org/virtio/virtio/v1.3/csd01/virtio-v1.3-csd01.html#x1-4850003 This takes only the payload into account, so it’s true that this problem exists; however, perhaps we should also inform the other peer of a lower credit balance, otherwise the other peer will believe it has much more credit than it actually does, send a large payload, and then the packet will be discarded and the data lost (there are no retransmissions, etc.).I dunno, perhaps revert 077706165717 ("virtio/vsock: don't use skbuff state to account credit") and find a better fix then?
IIRC the same issue was there before the commit fixed by that one (commit 71dc9ec9ac7d ("virtio/vsock: replace virtio_vsock_pkt with sk_buff")), so not sure about reverting it TBH.
CCing Arseniy and Bobby.
There is always a discrepancy between skb->len and skb->truesize. You will not be able to announce a 1MB window, and accept one milliion skb of 1-byte each. This kind of contract is broken.
Yep, I agree, but before we start discarding data (and losing it), IMHO we should at least inform the other peer that we're out of space.
@Stefan, @Michael, do you think we can do something in the spec to avoid this issue and in some way take into account also the metadata in the credit. I mean to avoid the 1-byte packets flooding.
Thanks, Stefano
