From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Lieven Subject: Re: tap devices not receiving packets from a bridge Date: Tue, 22 Jan 2013 10:04:07 +0100 Message-ID: <50FE5607.9020405@dlhnet.de> References: <50AE36E0.8000307@dlhnet.de> <20121123070211.GC22787@stefanha-thinkpad.hitronhub.home> <20121123110146.GC7051@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, netdev@vger.kernel.org To: "Michael S. Tsirkin" Return-path: In-Reply-To: <20121123110146.GC7051@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: netdev.vger.kernel.org On 23.11.2012 12:01, Michael S. Tsirkin wrote: > On Fri, Nov 23, 2012 at 10:41:21AM +0100, Peter Lieven wrote: >> >> Am 23.11.2012 um 08:02 schrieb Stefan Hajnoczi: >> >>> On Thu, Nov 22, 2012 at 03:29:52PM +0100, Peter Lieven wrote: >>>> is anyone aware of a problem with the linux network bridge that in very rare circumstances stops >>>> a bridge from sending pakets to a tap device? >>>> >>>> My problem occurs in conjunction with vanilla qemu-kvm-1.2.0 and Ubuntu Kernel 3.2.0-34.53 >>>> which is based on Linux 3.2.33. >>>> >>>> I was not yet able to reproduce the issue, it happens in really rare cases. The symptom is that >>>> the tap does not have any TX packets. RX is working fine. I see the packets coming in at >>>> the physical interface on the host, but they are not forwarded to the tap interface. >>>> The bridge itself has learnt the mac address of the vServer that is connected to the tap interface. >>>> It does not help to toggle the bridge link status, the tap interface status or the interface in the vServer. >>>> It seems that problem occurs if a tap interface that has previously been used, but set to nonpersistent >>>> is set persistent again and then is by chance assigned to the same vServer (=same mac address on same >>>> bridge) again. Unfortunately it seems not to be reproducible. >>> >>> Not sure but this patch from Michael Tsirkin may help - it solves an >>> issue with persistent tap devices: >>> >>> http://patchwork.ozlabs.org/patch/198598/ >> >> Hi Stefan, >> >> thanks for the pointer. I have seen this patch, but I have neglected it because it was dealing >> with persistent taps. But maybe the taps in the kernel are not deleted directly. >> Can you remember what the syptomps of the above issue have been? Sorry for >> being vague, but I currently have no clue whats going on. >> >> Can someone who has more internal knowledge of the bridging/tap code say if qemu can >> be responsible at all if the tap device is not receiving packets from the bridge. >> >> If I have the following config. Lets say packets coming in via physical interface eth1.123, >> and a bridge called br123.I further have a virtual machine with tap0. Both eth1.123 >> and tap0 are member of br123. >> >> If the issue occurs the vServer has no network connectivity inbound. If I sent a ping >> from the vServer I see it on tap0 and leaving on eth1.123. I see further the arp reply coming >> in via eth1.123, but the reply can't be seen on tap0. >> >> Peter > > If guest is not consuming packets, a TX queue in tap device > will with time overrun (there's space for 1000 packets there). > This is code from tun: > > if (skb_queue_len(&tfile->socket.sk->sk_receive_queue) > >= dev->tx_queue_len / tun->numqueues){ > if (!(tun->flags & TUN_ONE_QUEUE)) { > /* Normal queueing mode. */ > /* Packet scheduler handles dropping of further > * packets. */ > netif_stop_subqueue(dev, txq); > > /* We won't see all dropped packets > * individually, so overrun > * error is more appropriate. */ > dev->stats.tx_fifo_errors++; > > > So you can detect that this triggered by looking at fifo errors counter in device. > > Once this happens TX queue is stopped, then you hit this path: > > if (!netif_xmit_stopped(txq)) { > __this_cpu_inc(xmit_recursion); > rc = dev_hard_start_xmit(skb, dev, txq); > __this_cpu_dec(xmit_recursion); > if (dev_xmit_complete(rc)) { > HARD_TX_UNLOCK(dev, txq); > goto out; > } > } > > so packets are not passed to device anymore. > It will stay this way until guest consumes some packets and > queue is restarted. After some time I again have a vServer in this state. It seems not like there are no TX errors. # ifconfig tap10 tap10 Link encap:Ethernet HWaddr 7a:59:20:6f:e7:e5 inet6 addr: fe80::7859:20ff:fe6f:e7e5/64 Scope:Link UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:197431 errors:0 dropped:0 overruns:0 frame:0 TX packets:264309 errors:0 dropped:0 overruns:2 carrier:0 collisions:0 txqueuelen:500 RX bytes:13842063 (13.8 MB) TX bytes:35092821 (35.0 MB) It seems like the bridge is not forwarding any packets to the tap device anymore altough it has learnt the MAC-Adresses and there are also broadcast packets coming in. Any more ideas where I could debug? Peter > >>> >>> Stefan