NACK[N]/Cmnt: [SRU][F,J,L,M,N][PATCH 0/1] Hotplugging SCSI disk in QEMU VM fails

[Stefan Bader]

On 26.12.23 07:26, Chengen Du wrote:
> BugLink: https://bugs.launchpad.net/bugs/2047382
> 
> SRU Justification:
> 
> [Impact]
> Hot-plugging SCSI disks for QEMU VMs booting with UEFI and using guest kernels >= 6.5 might be broken.
> The inconsistency suggests a potential race condition.
> 
> [Fix]
> Reverting the two specified commits appears to restore reliability.
> ==========
> cc22522fd55e2 PCI: acpiphp: Use pci_assign_unassigned_bridge_resources() only for non-root bus
> 40613da52b13f PCI: acpiphp: Reassign resources on bridge if necessary
> ==========
> 
> Upstream has resolved the issue by reverting both commits through a commit placed below.
> ==========
> 5df12742b7e3a Revert "PCI: acpiphp: Reassign resources on bridge if necessary
> ==========
> 
> [Test Plan]
> 1. Create a VM
> virt-install --name scsi_test --memory 2048 --vcpus 2 --boot uefi --disk path=/home/ubuntu/mantic-server-cloudimg-amd64.img,size=20,format=qcow2,bus=virtio -os-variant=ubuntu18.04 --graphics spice --network bridge=virbr0
> 2. Prepare two XMLs for adding two disk devices
> # cat disk_X.xml
> <disk type='file' device='disk'>
>    <driver name='qemu' type='raw'/>
>    <source file='XXX.img'/>
>    <target dev='vdX' bus='virtio'/>
> </disk>
> 3. Hotplug disks and check for success
> virsh attach-device scsi_test disk_X.xml
> 
> [Where problems could occur]
> The patch reverts two commits that previously addressed long-standing issues related to hotplugging devices with large BARs.
> While this reversion may reintroduce legacy issues, it does not introduce new problems.
> The associated risks are deemed low, making it worthwhile to address timing issues during the hotplugging of SCSI disks in QEMU VM.
> 
> Bjorn Helgaas (1):
>    Revert "PCI: acpiphp: Reassign resources on bridge if necessary"
> 
>   drivers/pci/hotplug/acpiphp_glue.c | 9 +++------
>   1 file changed, 3 insertions(+), 6 deletions(-)
> 

Rejected for the following reasons:
- The change is already included in Noble with 6.7.

-Stefan
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