vhost: fix skb leak in handle_rx() (6e474083) · Commits · 戴 / test

Matthew found a roughly 40% tcp throughput regression with commit (vhost_net: try batch dequing from skb array) as discussed in the following thread: https://www.mail-archive.com/netdev@vger.kernel.org/msg187936.html Eventually we figured out that it was a skb leak in handle_rx() when sending packets to the VM. This usually happens when a guest can not drain out vq as fast as vhost fills in, afterwards it sets off the traffic jam and leaks skb(s) which occurs as no headcount to send on the vq from vhost side. This can be avoided by making sure we have got enough headcount before actually consuming a skb from the batched rx array while transmitting, which is simply done by moving checking the zero headcount a bit ahead. Signed-off-by:

Wei Xu <wexu@redhat.com> Reported-by:

Matthew Rosato <mjrosato@linux.vnet.ibm.com> Acked-by:

Michael S. Tsirkin <mst@redhat.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

drivers/vhost/net.c

+10 −10

Original line number	Diff line number	Diff line
		@@ -778,16 +778,6 @@ static void handle_rx(struct vhost_net *net)
		/* On error, stop handling until the next kick. */
		if (unlikely(headcount < 0))
		goto out;
		if (nvq->rx_array)
		msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
		/* On overrun, truncate and discard */
		if (unlikely(headcount > UIO_MAXIOV)) {
		iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
		err = sock->ops->recvmsg(sock, &msg,
		1, MSG_DONTWAIT \| MSG_TRUNC);
		pr_debug("Discarded rx packet: len %zd\n", sock_len);
		continue;
		}
		/* OK, now we need to know about added descriptors. */
		if (!headcount) {
		if (unlikely(vhost_enable_notify(&net->dev, vq))) {
		@@ -800,6 +790,16 @@ static void handle_rx(struct vhost_net *net)
		* they refilled. */
		goto out;
		}
		if (nvq->rx_array)
		msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
		/* On overrun, truncate and discard */
		if (unlikely(headcount > UIO_MAXIOV)) {
		iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
		err = sock->ops->recvmsg(sock, &msg,
		1, MSG_DONTWAIT \| MSG_TRUNC);
		pr_debug("Discarded rx packet: len %zd\n", sock_len);
		continue;
		}
		/* We don't need to be notified again. */
		iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len);
		fixup = msg.msg_iter;

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