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

[Thomas Huth]

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** Changed in: qemu
       Status: New => Incomplete

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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:
  Incomplete

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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