Reproduced this bug with fixed in 2.6.32-71.15.1.el6using the steps in:https://bugzilla.redhat.com/show_bug.cgi?id=624628#c24 and The sigio test are all FAIL.

Verified on 2.6.32-71.16.1.el6(guest's kernel) using the same steps and sigio test are all pass:
# ./run-test.sh
/usr/libexec/qemu-kvm -drive file=/home/rhel6.0_64.qcow2,if=none,id=test,boot=on,cache=none,format=qcow2,werror=stop,rerror=stop -device virtio-blk-pci,drive=test -chardev socket,path=/tmp/amit/test0,server,nowait,id=test0 -chardev socket,path=/tmp/amit/test1,server,nowait,id=test1 -chardev socket,path=/tmp/amit/test2,server,nowait,id=test2 -chardev socket,path=/tmp/amit/test3,server,nowait,id=test3 -chardev socket,path=/tmp/amit/test4,server,nowait,id=test4 -device virtio-serial -device virtconsole,chardev=test0,name=console.0 -device virtserialport,chardev=test1,name=test1 -device virtserialport,chardev=test2,name=test2 -device virtserialport,chardev=test3,name=test3 -device virtserialport,chardev=test4,name=test4 -vnc :1 -net none -enable-kvm -m 1G -serial file:/tmp/amit/test-serial.log -monitor unix:/tmp/amit/test-monitor,server,nowait -snapshot -smp 2
Using CPU model "cpu64-rhel6"
Using CPU model "cpu64-rhel6"
Guest is up 1
.........
       test_sigio_handler -  enabled (      open): PASS
       test_sigio_handler -  enabled (        in): PASS
       test_sigio_handler -  enabled (     close): PASS
       test_sigio_handler -  enabled (  multi-c2): PASS
       test_sigio_handler -  enabled (  multi-c3): PASS
       test_sigio_handler -  enabled (  multi-c4): PASS
       test_sigio_handler -  enabled (poll-sigio): PASS
.........

sorry for pasting wrong verified info here, change it back to ON_QA.

Reproduced this bug with qemu-kvm-0.12.1.2-2.146 and guest kernel 2.6.32-71.14.1.el6 using the following steps, guest hang after hotplugging virtserialport during file transfer from guest to host, tried 4 times, failed 4 times.

Verified this bug with qemu-kvm-0.12.1.2-2.146 and guest kernel 2.6.32-71.16.1.el6 using the following steps, guest runs normally after hotplugging virtserialport during file transfer from guest to host and dd reports "dd: write '/dev/vport0p1' : No such device", tried 4 times, pass 4 times.

steps:
1. start guest
# /usr/libexec/qemu-kvm -m 2G -smp 2  -uuid `uuidgen` -rtc base=utc,clock=host,driftfix=slew -boot c -drive file=/home/rhel6.0_64.qcow2,index=0,if=none,id=drive-virtio-disk1,media=disk,cache=none,format=qcow2 -device virtio-blk-pci,bus=pci.0,drive=drive-virtio-disk1,id=virtio-disk0 -netdev tap,id=hostnet0,vhost=on -device virtio-net-pci,netdev=hostnet0,mac=20:20:20:51:29:71,bus=pci.0,addr=0x7,id=hostnet0 -monitor unix:'/tmp/monitor-humanmonitor1-20100625-165355-sNdR',server,nowait -serial stdio -vnc :1 -device virtio-serial-pci,id=virtio-serial0,max_ports=16,bus=pci.0,addr=0x4 -chardev socket,id=channel0,path=/home/rhel6.channel0,server,nowait -device virtserialport,chardev=channel0,name=org.linux-kvm.port.0,bus=virtio-serial0.0,id=port1
2. in host:
#nc -U /home/rhel6.channel0
3. in guest:
# dd if=/dev/vda of=/dev/vport0p1 bs=1M count=1024
4. hot-unplug the port in monitor during the date transferring
(qemu) device_del port1

(In reply to comment #6)
> Reproduced this bug with qemu-kvm-0.12.1.2-2.146 and guest kernel
> 2.6.32-71.14.1.el6 using the following steps, guest hang after hotplugging
s/hotplugging/hot-unplugging
> virtserialport during file transfer from guest to host, tried 4 times, failed 4
> times.
> 
> Verified this bug with qemu-kvm-0.12.1.2-2.146 and guest kernel
> 2.6.32-71.16.1.el6 using the following steps, guest runs normally after
> hotplugging virtserialport during file transfer from guest to host and dd
s/hotplugging/hot-unplugging
> reports "dd: write '/dev/vport0p1' : No such device", tried 4 times, pass 4
> times.
> 
> steps:
> 1. start guest
> # /usr/libexec/qemu-kvm -m 2G -smp 2  -uuid `uuidgen` -rtc
> base=utc,clock=host,driftfix=slew -boot c -drive
> file=/home/rhel6.0_64.qcow2,index=0,if=none,id=drive-virtio-disk1,media=disk,cache=none,format=qcow2
> -device virtio-blk-pci,bus=pci.0,drive=drive-virtio-disk1,id=virtio-disk0
> -netdev tap,id=hostnet0,vhost=on -device
> virtio-net-pci,netdev=hostnet0,mac=20:20:20:51:29:71,bus=pci.0,addr=0x7,id=hostnet0
> -monitor unix:'/tmp/monitor-humanmonitor1-20100625-165355-sNdR',server,nowait
> -serial stdio -vnc :1 -device
> virtio-serial-pci,id=virtio-serial0,max_ports=16,bus=pci.0,addr=0x4 -chardev
> socket,id=channel0,path=/home/rhel6.channel0,server,nowait -device
> virtserialport,chardev=channel0,name=org.linux-kvm.port.0,bus=virtio-serial0.0,id=port1
> 2. in host:
> #nc -U /home/rhel6.channel0
> 3. in guest:
> # dd if=/dev/vda of=/dev/vport0p1 bs=1M count=1024
> 4. hot-unplug the port in monitor during the date transferring
> (qemu) device_del port1

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-2011-0283.html

    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:
The virtio-console device did not handle the hot-unplug operation properly. As a result, virtio-console could access the memory outside the driver's memory area and cause kernel panic on the guest. With this update, multiple fixes to the virtio-console device resolved this issue and the hot-unplug operation works as expected.