From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753352AbdK2Bxt (ORCPT ); Tue, 28 Nov 2017 20:53:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:40626 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752187AbdK2Bxr (ORCPT ); Tue, 28 Nov 2017 20:53:47 -0500 Subject: Re: [PATCH net,stable] vhost: fix skb leak in handle_rx() To: wexu@redhat.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Cc: mst@redhat.com, mjrosato@linux.vnet.ibm.com References: <1511889436-12876-1-git-send-email-wexu@redhat.com> From: Jason Wang Message-ID: <9b234fdd-baa3-f919-6c72-f6768265f1ca@redhat.com> Date: Wed, 29 Nov 2017 09:53:37 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0 MIME-Version: 1.0 In-Reply-To: <1511889436-12876-1-git-send-email-wexu@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 29 Nov 2017 01:53:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017年11月29日 01:17, wexu@redhat.com wrote: > 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 deferring it a moment later > in this patch. > > Signed-off-by: Wei Xu > --- > drivers/vhost/net.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c > index 8d626d7..e76535e 100644 > --- a/drivers/vhost/net.c > +++ b/drivers/vhost/net.c > @@ -778,8 +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)) { You need do msg.msg_control = vhost_net_buf_consume() here too, otherwise we may still get it leaked. Thanks > iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); > @@ -809,6 +807,8 @@ static void handle_rx(struct vhost_net *net) > */ > iov_iter_advance(&msg.msg_iter, vhost_hlen); > } > + if (nvq->rx_array) > + msg.msg_control = vhost_net_buf_consume(&nvq->rxq); > err = sock->ops->recvmsg(sock, &msg, > sock_len, MSG_DONTWAIT | MSG_TRUNC); > /* Userspace might have consumed the packet meanwhile: