On 29/12/23 00:18, Lukas Wunner wrote:
On Thu, Dec 28, 2023 at 01:03:10PM +1100, Steven Haigh wrote:
At some point in kernel 6.6.x, SCSI hotplug in qemu VMs broke. This was
mostly fixed in the following commit to release 6.6.8:
commit 5cc8d88a1b94b900fd74abda744c29ff5845430b
Author: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Date: Thu Dec 14 09:08:56 2023 -0600
Revert "PCI: acpiphp: Reassign resources on bridge if necessary"
After this commit, the SCSI block device is hotplugged correctly, and a device node as /dev/sdX appears within the qemu VM.
New problem:
When the same SCSI block device is hot-unplugged, the QEMU KVM process will
spin at 100% CPU usage. The guest shows no CPU being used via top, but the
host will continue to spin in the KVM thread until the VM is rebooted.
Find out the PID of the qemu process on the host, then cat /proc/$PID/stack
to see where the CPU time is spent.
Thanks for the tip - I'll certainly do that.
Annoyingly, since I posted this report originally, then adding in a new report to the kernel.org lists in this, I have
been unable to reproduce this problem. I have successfully done ~22 scsi hotplug / remove cycles and none resulted in
reproducing the issue.
Kernel versions are still the same on both proxmox host and the Fedora guest - however I see an update on the host of
the qemu-kvm packages in Proxmox. The proxmox host hasn't even been rebooted in this time.
I wonder if the initial revert included in 6.6.8 fixed the main problem, and the later update to qemu-kvm packages on
the proxmox host followed by the last reboot of the VM with the new KVM package sorted the second issue.
Seeing as I can no longer reproduce this reliably - whereas it was 100% reproducible prior, maybe I'm now chasing ghosts.
I'll still continue to monitor - as I normally do this SCSI hotplug ~3 times per week doing backups to different
external HDDs - so if I do observe it again, I'll grab the stack and reply to this thread again with what I can find.
Until then, I don't want to waste other peoples time also chasing ghosts :)
--
Steven Haigh
📧 netwiz@xxxxxxxxx
💻 https://crc.id.au
