[Qemu-devel] question: disk missing in the guest contingently when hotplug several virtio scsi disks consecutively.

[l00284672]

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>
    <controller type='scsi' index='1' model='virtio-scsi'>
      <driver iothread='27'/>
      <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='28'/>
      <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='29'/>
      <alias name='scsi3'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x0c' 
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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