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Bug 674539

Summary: slow guests block other guests on the same lan
Product: Red Hat Enterprise Linux 6 Reporter: Michael S. Tsirkin <mst>
Component: qemu-kvmAssignee: Michael S. Tsirkin <mst>
Status: CLOSED ERRATA QA Contact: Virtualization Bugs <virt-bugs>
Severity: high Docs Contact:
Priority: unspecified    
Version: 6.0CC: akong, bcao, ehabkost, mjenner, mkenneth, tburke, virt-maint
Target Milestone: rc   
Target Release: ---   
Hardware: Unspecified   
OS: Unspecified   
Whiteboard:
Fixed In Version: qemu-kvm-0.12.1.2-2.136.el6 Doc Type: Bug Fix
Doc Text:
Cause: qemu-kvm tap code default for 'sndbuf' can prevent another guest from transmitting any packets. Consequence: sending packets from guest to another guest that do not consume the packets can cause all networking from said guest to get blocked. Fix: default of 'sndbuf' option changed to 0, disabling sndbuf. Result: guest networking is not blocked even when it is sending packets to another guest that is not consuming the packets.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2011-05-19 11:21:29 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 580954    

Comment 4 Amos Kong 2011-02-19 10:42:27 UTC 
I could not reproduce this bug with (qemu-kvm-0.12.1.2-2.129.el6.x86_64) by the steps in comment #0.

> Steps to Reproduce:
> 1. create multiple guests connected to a bridge: A,B,C,D
> 2. force arp in guest A to match guest B
> arp -i eth0 -s <ip for guest B> <mac for guest B>

execute in guest A ?
>   repeat for guests C, D

execute in guest C ?
> 3. ping guest B, we should get back packets
>    e.g. with -c 1

ping from guest A ?
>    repeat for C, D

ping from guest A ?
> 3. ifdown guest B

guest B) # ifconfig eth0 down
>     repeat for C,D

guest D) # ifconfig eth0 down
> 4. log into guest A
>  ping -f -c 2000 -s 1000 B_ip -i 0.01

ping from guest A?
>    repeat for C, D

ping from guest A?
> Actual results:
> outgoing networking from A is blocked.
> E.g. A does not reply to ping.

ping from host?
> Expected results:
> networking from A to C,D is blocked,
> networking from A to host works

qemu commandline
# qemu-kvm -name guesta -chardev socket,id=human_monitor_Knqg,path=/tmp/monitor-humanmonitor1-20110219-174500-2Nk6,server,nowait -mon chardev=human_monitor_Knqg,mode=readline -chardev socket,id=serial_2QM1,path=/tmp/s1,server,nowait -device isa-serial,chardev=serial_2QM1 -drive file=/home/autotest-devel/client/tests/kvm/images/RHEL-Server-6.0-64-virtio.qcow2,index=0,if=none,id=drive-virtio-disk1,media=disk,cache=none,snapshot=on,format=qcow2,aio=native -device virtio-blk-pci,bus=pci.0,addr=0x4,drive=drive-virtio-disk1,id=virtio-disk1 -device virtio-net-pci,netdev=idkZj2Gr,mac=9a:76:6e:ab:5c:3f,netdev=idkZj2Gr,id=ndev00idkZj2Gr,bus=pci.0,addr=0x3 -netdev tap,id=idkZj2Gr,vhost=on,ifname=t0-174500-2Nk6,script=/home/autotest-devel/client/tests/kvm/scripts/qemu-ifup-switch,downscript=no -m 512 -smp 2,cores=1,threads=1,sockets=2 -cpu cpu64-rhel6,+sse2,+x2apic -vnc :0 -rtc base=utc,clock=host,driftfix=none -boot order=cdn,once=c,menu=off -usbdevice tablet -no-kvm-pit-reinjection -enable-kvm
Comment 8 Eduardo Habkost 2011-05-03 19:26:06 UTC 
    Technical note added. If any revisions are required, please edit the "Technical Notes" field
    accordingly. All revisions will be proofread by the Engineering Content Services team.
    
    New Contents:
Cause: qemu-kvm tap code default for 'sndbuf' can prevent another guest from transmitting any packets.

Consequence: sending packets from guest to another guest that do not consume the packets can cause all networking from said guest to get blocked.

Fix: default of 'sndbuf' option changed to 0, disabling sndbuf.

Result: guest networking is not blocked even when it is sending packets to another guest that is not consuming the packets.
Comment 9 errata-xmlrpc 2011-05-19 11:21:29 UTC 
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2011-0534.html
Comment 10 errata-xmlrpc 2011-05-19 13:01:24 UTC 
An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHSA-2011-0534.html