Re: [Xen-devel] xennet: skb rides the rocket messages in domU dmesg

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 05/26/2010 02:21 PM, Mark Hurenkamp wrote:
> Hi,
>
>
> On my home server i am running Xen-4.0.1-rc1 with a recent xen/next
> kernel,

Are you actually using the "xen/next" branch?  I recommend you use
xen/stable-2.6.32.x, since that's tracking all the other bugfixes going
into Linux 2.6.32.

> and a pvm domU with the same kernel, and 4 tuners passed through.
> Because the mythtv backend domain would sometimes become unstable, i
> decided
> to split up my mythtv backend into 3 seperate virtual machines, one
> master
> backend with the database, and 2 slave backends with the tuners.
> One of the slave backends has a cx23885 based dvb tuner card, the
> other slave
> backend runs 3 ivtv based tuners.
> To keep consistency with old recording data, and since i would like to
> have all
> recordings in a single volume, i tried to use an nfs mount of the
> recordings volume
> from the dom0 to mount on all backends. This resulted in a very
> unstable system,
> to the point where my most important slave backend became unusable.

Unstable how?

> So i tried it the other way, have the slave backends each mount their own
> recordings volume as a block device via xen, and for backwards
> compatibility mount
> the volume which holds the old recordings via nfs on the master backend.
>
> Now i see many "xennet: skb rides the rocket" messages appear in the
> (pv) slave
> backend which exports the recordings volume to the master backend. These
> messages i did not see when there was only a single mythtv backend.
> (both the dom0 as well as the mythtv domUs are ubuntu lucid server based)
> Overall the system seems to perform ok, and the messages are not
> causing the
> system to become unusable or more unstable, so it is not a major issue.

That appears to mean that you're getting single packets which are larger
than 18 pages long (72k).  I'm not quite sure how that's possible, since
I thought the datagram limit is 64k..

Are you using nfs over udp or tcp?  (I think tcp, from your stack trace.)

Does turning of tso/gso with ethtool make a difference?

    J

>
> Note that both the master backend, and the slave backend which exports
> the
> volume, are paravirtualised domains. The slave backend has the following
> xen config:
>
> kernel = '/boot/vmlinuz-2.6.32m5'
> ramdisk = '/boot/initrd.img-2.6.32m5'
> extra = 'root=/dev/xvda1 ro console=hvc0 noirqdebug iommu=soft
> swiotlb=force'
> maxmem = '1000'
> memory = '500'
> device_model='/usr/lib/xen/bin/qemu-dm'
> serial='pty'
> disk = [
>     'phy:/dev/vm/tilnes-lucid,hda,w',
>     'phy:/dev/mythtv/recordings,hdb,w',
> ]
> boot='c'
> name = 'tilnes'
> vif = [ 'mac=aa:20:00:00:01:72, bridge=loc' ]
> vfb = [ 'vnc=1,vnclisten=0.0.0.0,vncdisplay=5' ]
>
> usb=1
> usbdevice='tablet'
> monitor=1
> pci = [
>     '0000:08:02.0',
>     '0000:09:08.0',
>     '0000:09:09.0',
>     ]
> vcpus=8
>
>
> The messagedump i see (this is only 1 example, my dmesg is full of
> these):
>
> xennet: skb rides the rocket: 20 frags
> Pid: 3237, comm: nfsd Tainted: G      D    2.6.32m5 #9
> Call Trace:
> <IRQ>  [<ffffffffa005e2d4>] xennet_start_xmit+0x75/0x678 [xen_netfront]
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff8136bd3a>] ? rcu_read_unlock+0x0/0x1e
>  [<ffffffff8100efdf>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff81076983>] ? lock_release+0x1e0/0x1ed
>  [<ffffffff8136ee0e>] dev_hard_start_xmit+0x236/0x2e1
>  [<ffffffff8138114e>] sch_direct_xmit+0x68/0x16f
>  [<ffffffff8136f240>] dev_queue_xmit+0x274/0x3de
>  [<ffffffff8136f130>] ? dev_queue_xmit+0x164/0x3de
>  [<ffffffff8139cf30>] ? dst_output+0x0/0xd
>  [<ffffffff8139e16d>] ip_finish_output2+0x1df/0x222
>  [<ffffffff8139e218>] ip_finish_output+0x68/0x6a
>  [<ffffffff8139e503>] ip_output+0x9c/0xa0
>  [<ffffffff8139e5a2>] ip_local_out+0x20/0x24
>  [<ffffffff8139ebfe>] ip_queue_xmit+0x309/0x37a
>  [<ffffffff8100e871>] ? xen_force_evtchn_callback+0xd/0xf
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff8100e871>] ? xen_force_evtchn_callback+0xd/0xf
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff813b012a>] tcp_transmit_skb+0x648/0x686
>  [<ffffffff813b2654>] tcp_write_xmit+0x808/0x8f7
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff813af7e2>] ? tcp_established_options+0x2e/0xa9
>  [<ffffffff813b279e>] __tcp_push_pending_frames+0x2a/0x58
>  [<ffffffff813ac124>] tcp_data_snd_check+0x24/0xea
>  [<ffffffff813ae464>] tcp_rcv_established+0xdd/0x6d4
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff813b535b>] tcp_v4_do_rcv+0x1ba/0x375
>  [<ffffffff8100efdf>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff813b62d1>] ? tcp_v4_rcv+0x2b3/0x6b7
>  [<ffffffff813b6474>] tcp_v4_rcv+0x456/0x6b7
>  [<ffffffff8139ad27>] ? ip_local_deliver_finish+0x0/0x235
>  [<ffffffff8139ae9b>] ip_local_deliver_finish+0x174/0x235
>  [<ffffffff8139ad6b>] ? ip_local_deliver_finish+0x44/0x235
>  [<ffffffff8139afce>] ip_local_deliver+0x72/0x7c
>  [<ffffffff8139a89d>] ip_rcv_finish+0x3cd/0x3fb
>  [<ffffffff8139ab84>] ip_rcv+0x2b9/0x2f9
>  [<ffffffff813ec764>] ? packet_rcv_spkt+0xd6/0xe1
>  [<ffffffff8136e065>] netif_receive_skb+0x445/0x46f
>  [<ffffffff810c0b92>] ? free_hot_page+0x3a/0x3f
>  [<ffffffffa005f41d>] xennet_poll+0xaf4/0xc7b [xen_netfront]
>  [<ffffffff8136e7ac>] net_rx_action+0xab/0x1df
>  [<ffffffff81076983>] ? lock_release+0x1e0/0x1ed
>  [<ffffffff81053842>] __do_softirq+0xe0/0x1a2
>  [<ffffffff8109e984>] ? handle_level_irq+0xd1/0xda
>  [<ffffffff8126a152>] ? __xen_evtchn_do_upcall+0x12e/0x163
>  [<ffffffff81012cac>] call_softirq+0x1c/0x30
>  [<ffffffff8101428d>] do_softirq+0x41/0x81
>  [<ffffffff81053694>] irq_exit+0x36/0x78
>  [<ffffffff8126a646>] xen_evtchn_do_upcall+0x37/0x47
>  [<ffffffff81012cfe>] xen_do_hypervisor_callback+0x1e/0x30
> <EOI>  [<ffffffff8111dc4a>] ? __bio_add_page+0xee/0x212
>  [<ffffffff8111df9b>] ? bio_alloc+0x10/0x1f
>  [<ffffffff811217e1>] ? mpage_alloc+0x25/0x7d
>  [<ffffffff8111dd9f>] ? bio_add_page+0x31/0x33
>  [<ffffffff81121dde>] ? do_mpage_readpage+0x3d3/0x488
>  [<ffffffff810bba3b>] ? add_to_page_cache_locked+0xcc/0x108
>  [<ffffffff81121fbb>] ? mpage_readpages+0xcb/0x10f
>  [<ffffffff81159aee>] ? ext3_get_block+0x0/0xf9
>  [<ffffffff81159aee>] ? ext3_get_block+0x0/0xf9
>  [<ffffffff81157bbc>] ? ext3_readpages+0x18/0x1a
>  [<ffffffff810c387b>] ? __do_page_cache_readahead+0x140/0x1cd
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff8100efdf>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff810c3924>] ? ra_submit+0x1c/0x20
>  [<ffffffff810c3d1c>] ? ondemand_readahead+0x1de/0x1f1
>  [<ffffffff810c3dc3>] ? page_cache_sync_readahead+0x17/0x1c
>  [<ffffffff81118790>] ? __generic_file_splice_read+0xf0/0x41a
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff811c0c07>] ? rcu_read_unlock+0x0/0x1e
>  [<ffffffff8100efdf>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffff81076983>] ? lock_release+0x1e0/0x1ed
>  [<ffffffff811c0c23>] ? rcu_read_unlock+0x1c/0x1e
>  [<ffffffff811c16e2>] ? avc_has_perm_noaudit+0x3b5/0x3c7
>  [<ffffffff810ec8eb>] ? check_object+0x170/0x1a9
>  [<ffffffff8100e871>] ? xen_force_evtchn_callback+0xd/0xf
>  [<ffffffff8111770d>] ? spd_release_page+0x0/0x14
>  [<ffffffff811c4d62>] ? selinux_file_permission+0x57/0xae
>  [<ffffffff81118afe>] ? generic_file_splice_read+0x44/0x72
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff811171d4>] ? do_splice_to+0x6c/0x79
>  [<ffffffff8100eff2>] ? check_events+0x12/0x20
>  [<ffffffff811178ed>] ? splice_direct_to_actor+0xc2/0x1a1
>  [<ffffffff8100efdf>] ? xen_restore_fl_direct_end+0x0/0x1
>  [<ffffffffa01a0b53>] ? nfsd_direct_splice_actor+0x0/0x12 [nfsd]
>  [<ffffffffa01a0a44>] ? nfsd_vfs_read+0x276/0x385 [nfsd]
>  [<ffffffffa01a115a>] ? nfsd_read+0xa1/0xbf [nfsd]
>  [<ffffffffa00de128>] ? svc_xprt_enqueue+0x22b/0x238 [sunrpc]
>  [<ffffffffa01a7cbf>] ? nfsd3_proc_read+0xe2/0x121 [nfsd]
>  [<ffffffffa00d6551>] ? cache_put+0x2d/0x2f [sunrpc]
>  [<ffffffffa019c36f>] ? nfsd_dispatch+0xec/0x1c7 [nfsd]
>  [<ffffffffa00d2e99>] ? svc_process+0x436/0x637 [sunrpc]
>  [<ffffffffa01a4418>] ? exp_readlock+0x10/0x12 [nfsd]
>  [<ffffffffa019c8c0>] ? nfsd+0xf3/0x13e [nfsd]
>  [<ffffffffa019c7cd>] ? nfsd+0x0/0x13e [nfsd]
>  [<ffffffff8106601d>] ? kthread+0x7a/0x82
>  [<ffffffff81012baa>] ? child_rip+0xa/0x20
>  [<ffffffff81011ce6>] ? int_ret_from_sys_call+0x7/0x1b
>  [<ffffffff81012526>] ? retint_restore_args+0x5/0x6
>  [<ffffffff81012ba0>] ? child_rip+0x0/0x20
>
>
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