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

[Tim Gardner]

On 1/3/24 7:42 PM, Chengen Du wrote:
> Hi Tim,
> 
> Upstream has reverted two commits in a single commit, and you can find it here:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5df12742b7e3aae2594a30a9d14d5d6e9e7699f4
> 
> I have directly backported this commit to address the revert of the
> related commits.
> 

Indeed. Must read for content...

> Best regards,
> Chengen Du
> 
> On Thu, Jan 4, 2024 at 12:54 AM Tim Gardner <tim.gardner at canonical.com> wrote:
>>
>> On 12/25/23 11:26 PM, 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(-)
>>>
>>
>> You mention reverting 2 patches, but I only see one.
>> --
>> -----------
>> Tim Gardner
>> Canonical, Inc
>>
Acked-by: Tim Gardner <tim.gardner at canonical.com>
-- 
-----------
Tim Gardner
Canonical, Inc