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 10:43:34 +0100 Message-ID: <50FE5F46.50500@dlhnet.de> References: <50AE36E0.8000307@dlhnet.de> <20121123070211.GC22787@stefanha-thinkpad.hitronhub.home> <20121123110146.GC7051@redhat.com> <50FE5607.9020405@dlhnet.de> 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: <50FE5607.9020405@dlhnet.de> 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 22.01.2013 10:04, Peter Lieven wrote: > 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? Would like to add I see the packets in ebtables forwarding chain, but the TX counters of the interface are not increasing. Peter > > Peter > >> >>>> >>>> Stefan >