2018-01-15 11:26:15 +00:00
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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2017-12-04 08:08:19 +00:00
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From: Wei Xu <wexu@redhat.com>
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Date: Fri, 1 Dec 2017 05:10:36 -0500
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2018-01-15 11:26:15 +00:00
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Subject: [PATCH] vhost: fix skb leak in handle_rx()
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2017-12-04 08:08:19 +00:00
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Matthew found a roughly 40% tcp throughput regression with commit
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c67df11f(vhost_net: try batch dequing from skb array) as discussed
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in the following thread:
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https://www.mail-archive.com/netdev@vger.kernel.org/msg187936.html
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Eventually we figured out that it was a skb leak in handle_rx()
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when sending packets to the VM. This usually happens when a guest
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can not drain out vq as fast as vhost fills in, afterwards it sets
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off the traffic jam and leaks skb(s) which occurs as no headcount
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to send on the vq from vhost side.
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This can be avoided by making sure we have got enough headcount
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before actually consuming a skb from the batched rx array while
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transmitting, which is simply done by moving checking the zero
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headcount a bit ahead.
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Signed-off-by: Wei Xu <wexu@redhat.com>
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Reported-by: Matthew Rosato <mjrosato@linux.vnet.ibm.com>
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Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>
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---
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drivers/vhost/net.c | 20 ++++++++++----------
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1 file changed, 10 insertions(+), 10 deletions(-)
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diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
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index 1c75572f5a3f..010253847022 100644
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--- a/drivers/vhost/net.c
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+++ b/drivers/vhost/net.c
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@@ -781,16 +781,6 @@ static void handle_rx(struct vhost_net *net)
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/* On error, stop handling until the next kick. */
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if (unlikely(headcount < 0))
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goto out;
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- if (nvq->rx_array)
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- msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
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- /* On overrun, truncate and discard */
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- if (unlikely(headcount > UIO_MAXIOV)) {
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- iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
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- err = sock->ops->recvmsg(sock, &msg,
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- 1, MSG_DONTWAIT | MSG_TRUNC);
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- pr_debug("Discarded rx packet: len %zd\n", sock_len);
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- continue;
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- }
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/* OK, now we need to know about added descriptors. */
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if (!headcount) {
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if (unlikely(vhost_enable_notify(&net->dev, vq))) {
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@@ -803,6 +793,16 @@ static void handle_rx(struct vhost_net *net)
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* they refilled. */
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goto out;
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}
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+ if (nvq->rx_array)
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+ msg.msg_control = vhost_net_buf_consume(&nvq->rxq);
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+ /* On overrun, truncate and discard */
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+ if (unlikely(headcount > UIO_MAXIOV)) {
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+ iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1);
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+ err = sock->ops->recvmsg(sock, &msg,
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+ 1, MSG_DONTWAIT | MSG_TRUNC);
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+ pr_debug("Discarded rx packet: len %zd\n", sock_len);
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+ continue;
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+ }
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/* We don't need to be notified again. */
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iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len);
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fixup = msg.msg_iter;
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--
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2.14.2
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