Re: [Qemu-devel] [Bug 1779120] Re: disk missing in the guest contingently when hotplug several virtio scsi disks consecutively

[贞贵李]

Hi, Stefan.
(host)# rpm -qa | grep qemu-kvm
qemu-kvm-2.8.1-25.142.x86_64
(guest)# uname -r
3.10.0-514.el7.x86_64

I also tried the newest version of qemu-kvm, but it also met this issue.
The steps to reproduce this issue are below:

1)attach four virtio-scsi controller with dataplane to vm.
     <controller type='scsi' index='0' model='virtio-scsi'>
       <driver iothread='1'/>
       <alias name='scsi0'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x07' 
function='0x0'/>
     </controller>
     <controller type='scsi' index='1' model='virtio-scsi'>
       <driver iothread='2'/>
       <alias name='scsi1'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x0a' 
function='0x0'/>
     </controller>
     <controller type='scsi' index='2' model='virtio-scsi'>
       <driver iothread='3'/>
       <alias name='scsi2'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x0b' 
function='0x0'/>
     </controller>
     <controller type='scsi' index='3' model='virtio-scsi'>
       <driver iothread='4'/>
       <alias name='scsi3'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x0c' 
function='0x0'/>
     </controller>

2)attach 35 virtio-scsi disks(sda - sdai) to vm consecutively. One 
controller has 15 scsi disks.
A example of disk xml is below:
     <disk type='block' device='lun' rawio='yes'>
       <driver name='qemu' type='raw' cache='none' io='native'/>
       <source dev='/dev/mapper/360022a11000c1e0a0787bb2500000139'/>
       <backingStore/>
       <target dev='sda' bus='scsi'/>
       <shareable/>
       <alias name='scsi0-0-0-0'/>
       <address type='drive' controller='0' bus='0' target='0' unit='0'/>
     </disk>

    You can write a shell script like this:
        for((i=1;i++;i<=35))
        do
             virsh attach-device centos7.3_64_server scsi_disk_$i.xml 
--config --live
        done

This issue is a probabilistic event. If it does not appear, repeat the 
above steps several more times.
Thank you!

On 2018/6/28 21:01, Stefan Hajnoczi wrote:
> Please post the following information:
> (host)# rpm -qa | grep qemu-kvm
> (guest)# uname -r
>
> What are the exact steps to reproduce this issue (virsh command-lines
> and XML)?
>

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https://bugs.launchpad.net/bugs/1779120

Title:
  disk missing in the guest contingently when hotplug several virtio
  scsi disks consecutively

Status in QEMU:
  New

Bug description:
  Hi, I found a bug that disk missing (not all disks missing ) in the
  guest contingently when hotplug several virtio scsi disks
  consecutively.  After rebooting the guest,the missing disks appear
  again.

  The guest is centos7.3 running on a centos7.3 host and the scsi
  controllers are configed with iothread.  The scsi controller xml is
  below:

      <controller type='scsi' index='0' model='virtio-scsi'>
        <driver iothread='26'/>
        <alias name='scsi0'/>
        <address type='pci' domain='0x0000' bus='0x00' slot='0x07' 
function='0x0'/>
      </controller>

  If the scsi controllers are configed without iothread,  disks are all
  can be seen in the guest when hotplug several virtio scsi disks
  consecutively.

  I think the biggest difference between them is that scsi controllers
  with iothread call virtio_notify_irqfd to notify guest and scsi
  controllers without iothread call virtio_notify instead.  What make it
  difference? Will interrupts are lost when call virtio_notify_irqfd
  due to  race condition for some unknow reasons? Maybe guys more
  familiar with scsi dataplane can help. Thanks for your reply!

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