Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752624AbdLAFz3 (ORCPT ); Fri, 1 Dec 2017 00:55:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46218 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751265AbdLAFyl (ORCPT ); Fri, 1 Dec 2017 00:54:41 -0500 From: wexu@redhat.com To: virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: jasowang@redhat.com, mst@redhat.com, mjrosato@linux.vnet.ibm.com, wexu@redhat.com Subject: [PATCH 1/3] vhost: fix skb leak in handle_rx() Date: Fri, 1 Dec 2017 00:54:27 -0500 Message-Id: <1512107669-27572-2-git-send-email-wexu@redhat.com> In-Reply-To: <1512107669-27572-1-git-send-email-wexu@redhat.com> References: <1512107669-27572-1-git-send-email-wexu@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 01 Dec 2017 05:54:41 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2414 Lines: 64 From: Wei Xu 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: Wei Xu Reported-by: Matthew Rosato --- drivers/vhost/net.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-) diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c index 8d626d7..c7bdeb6 100644 --- a/drivers/vhost/net.c +++ b/drivers/vhost/net.c @@ -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; -- 1.8.3.1