From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jason Wang Subject: Re: [PATCH net,stable] vhost: fix skb leak in handle_rx() Date: Wed, 29 Nov 2017 13:06:28 +0800 Message-ID: <37f16bef-4a59-b895-c61b-e3f473617411@redhat.com> References: <1511889436-12876-1-git-send-email-wexu@redhat.com> <9b234fdd-baa3-f919-6c72-f6768265f1ca@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: mjrosato@linux.vnet.ibm.com, mst@redhat.com To: wexu@redhat.com, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Return-path: In-Reply-To: <9b234fdd-baa3-f919-6c72-f6768265f1ca@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On 2017年11月29日 09:53, Jason Wang wrote: > > > On 2017å¹´11月29æ—¥ 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 Not a leak actually, but the packet won't be consumed and we will hit UIO_MAXIOV forever in this case. Thanks