[ kvm-Bugs-2506814 ] TAP network lockup after some traffic

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Bugs item #2506814, was opened at 2009-01-14 11:38
Message generated for change (Comment added) made by cova
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Fabio Coatti (cova)
Assigned to: Nobody/Anonymous (nobody)
Summary: TAP network lockup after some traffic

Initial Comment:
Hi all,
we are experiencing severe network troubles using kvm+tap networking.
basically, after some network load (we have yet to identify the exact amount of traffic if one exist) network stops working. 
During lockups, With tcpdump we can see arp requests on guest interface, then on tap, brX and physical interfaces on host system.
the arp answers can be seen, with tcpdump, only on physical host interface and bridge (brX), but not on tap device. Basically it seems that packets coming from external network get lost in tap device on the way to guest (kvm). Looking at tap data with ifconfig, the only weird thing is the TX packets overrun count that is > 0. every time the network stops working, overrun count increases.
This has been observed with several kvm releases (for sure, 76/77/78/79/80/81/82) and with different kernels (tried with some versions among 2.6.25.X, 26.X, 27.X, 28) both on guest and host side.
we tried several network drivers (virtio, e1000, rtl) and all shows the same problem. Only 100Mbit drivers seems to be unaffected so far. (only virtio has acceptable performance)
(btw: on host machine we have vlan on top of ethX devices)
cpu number on guest makes no difference.
we tried with vanilla kernel provided kvm modules and with kvm package provided modules.
guest: 32 bit
host: 64 bit
host machine:

2 x Quad-Core AMD Opteron(tm) Processor 2352 16GB, gentoo.

Of course I can provide more details or perform other tests and try patches, if someone can give me some hints and advices they will be most welcome.

Thanks.




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>Comment By: Fabio Coatti (cova)
Date: 2009-05-07 10:51

Message:
We are still biten by this issue. I'm running out of ideas, but if someone
can give me some hints on how to track down the problem or at least collect
more information I'll try it.

Thanks.

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Comment By: Tais M. Hansen (mellen)
Date: 2009-05-07 10:39

Message:
Just happened again. Seems like it stops generating interrupts on virtio
devices:

 10:       3001      51199   IO-APIC-fasteoi   virtio1, virtio2
 11:    7694835    8468134   IO-APIC-fasteoi   virtio0

doing an /bin/ls froze the guest for a minute or so until a CTRL-C got
through. After /bin/ls:

 10:       3001      51220   IO-APIC-fasteoi   virtio1, virtio2
 11:    7694835    8468134   IO-APIC-fasteoi   virtio0

kvm_stat:
efer_reload                    0         0
exits                 19150288617      1082
fpu_reload             119767301        34
halt_exits             544721221       194
halt_wakeup            300187634       141
host_state_reload      837279034       259
hypercalls            4991133618         0
insn_emulation        4797940911       709
insn_emulation_fail            0         0
invlpg                         0         0
io_exits               281254462        65
irq_exits              173205458         0
irq_window                     0         0
largepages                     0         0
mmio_exits                720457         0
mmu_cache_miss         290275800         0
mmu_flooded            289036380         0
mmu_pde_zapped         170308104         0
mmu_pte_updated       6239297430         0
mmu_pte_write         20470585377         0
mmu_recycled                   0         0
mmu_shadow_zapped      335324686         0
pf_fixed              8324827214         0
pf_guest              2229555421         0
remote_tlb_flush       283772247         0
request_irq                    0         0
signal_exits                   6         0
tlb_flush             5334530556        66

... but there are 6 other guests on this host running just fine.

Can't connect gdb to the kvm's gdbserver. It just says "Remote 'g' packet
reply is too long: ...."

Issuing system_reset stalled for a minute, then rebooted the guest. After
reboot, guest is find again.

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Comment By: Tais M. Hansen (mellen)
Date: 2009-05-06 17:07

Message:
I'm curious about the status of this issue?

I'm experiencing the same problem apparently randomly on guests.
Restarting the network interface does not seem to fix the problem. Only a
reboot (or system_reset in kvm/qemu console) solves it.

Last time it happened was on a host with kvm-84 and guest with kernel
2.6.27 using virtio-net. Leading up to the stall it had a traffic load of
about 5 mbit constantly up and down for just over 2 hours with one 12 mbit
spikes.

I did not check interface counters or network traces at the time.


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Comment By: Fabio Coatti (cova)
Date: 2009-01-14 14:24

Message:
It seems quite similar indeed, but ip link set eth up/down on guest side
seems to have no effect. Besides that, looking at the thread you pointed
me, I can see another difference: sniffing on tap device in my case shows
only outgoing packets (i.e. leaving kvm guest).
So it can be the very same issue, but some differences are present.
At least, we are seeing this on newer kernels and kvm revisions :)


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Comment By: Mark McLoughlin (markmc)
Date: 2009-01-14 12:19

Message:
Does ifup/ifdown in the guest fix the hang?

If so, it sounds like the issue discussed in this long thread:

  http://www.mail-archive.com/kvm@vger.kernel.org/msg06774.html

We still haven't got to the bottom of it.

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You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=893831&aid=2506814&group_id=180599