Commit 6e474083 authored by Wei Xu's avatar Wei Xu Committed by David S. Miller

vhost: fix skb leak in handle_rx()

Matthew found a roughly 40% tcp throughput regression with commit
c67df11f(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: default avatarWei Xu <wexu@redhat.com>
Reported-by: default avatarMatthew Rosato <mjrosato@linux.vnet.ibm.com>
Acked-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent fa935ca2
...@@ -778,16 +778,6 @@ static void handle_rx(struct vhost_net *net) ...@@ -778,16 +778,6 @@ static void handle_rx(struct vhost_net *net)
/* On error, stop handling until the next kick. */ /* On error, stop handling until the next kick. */
if (unlikely(headcount < 0)) if (unlikely(headcount < 0))
goto out; 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. */ /* OK, now we need to know about added descriptors. */
if (!headcount) { if (!headcount) {
if (unlikely(vhost_enable_notify(&net->dev, vq))) { if (unlikely(vhost_enable_notify(&net->dev, vq))) {
...@@ -800,6 +790,16 @@ static void handle_rx(struct vhost_net *net) ...@@ -800,6 +790,16 @@ static void handle_rx(struct vhost_net *net)
* they refilled. */ * they refilled. */
goto out; 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. */ /* We don't need to be notified again. */
iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len); iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len);
fixup = msg.msg_iter; fixup = msg.msg_iter;
......
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