SRU Justification
[Impact]
Hot removal of disks under kvm on s390 does not result in the kernel removing the block device, which can lead to hung tasks and other issues.
[Test Plan]
See steps to reproduce the bug in the original description below. To test, execute these steps and confirm that the block device gets removed as expected.
[Where problems could occur]
The fix is a revert of the changes which introduced this regression. The original commit was a removal of supposedly unused code, but it seems a mistake was made in the logic around unregistering of disks. Reverting the changes could have potential to introduce bugs related to other virt devices, especially if it interacts badly with subsequent driver changes. However, the patch reverted cleanly, and reverting restores the code to the state which has been working well in previous kernels and seems like the lowest risk option until a proper fix is available upstream.
---
Repro:
#1 Get a guest
$ uvt-kvm create --disk 5 --password=ubuntu h release=hirsute arch=s390x label=daily
$ uvt-kvm wait h release=hirsute arch=s390x label=daily
#2 Attach and Detach disk
$ sudo qemu-img create -f qcow2 /var/lib/libvirt/images/test.qcow2 10M
$ virsh attach-disk h /var/lib/libvirt/images/test.qcow2 vdc
$ virsh detach-disk h vdc
From libvirts POV it is gone at this point
$ virsh domblklist h
Target Source
------------------------------------------------------------------
vda /var/lib/uvtool/libvirt/images/hirsute-2nd-zfs.qcow
vdb /var/lib/uvtool/libvirt/images/hirsute-2nd-zfs-ds.qcow
But the guest thinks still it is present
$ uvt-kvm ssh --insecure hirsute-2nd-zfs lsblk
...
vdc 252:32 0 20M 0 disk
This even remains a while after (not a race).
Any access to it in the guest will hang (as you'd expect of a non-existing blockdev)
4 0 1758 1739 20 0 12140 4800 - S+ pts/0 0:00 | \_ sudo mkfs.ext4 /dev/vdc
4 0 1759 1758 20 0 6924 1044 - D+ pts/0 0:00 | \_ mkfs.ext4 /dev/vdc
The result above was originally found with hirsute-guest@hirsute-host on s390x
I do NOT see the same with groovy-guest@hirsute-host on s390x
I DO see the same with hirsute-guest@groovy-host on s390x
=> Guest version dependent not Host/Hipervisor dependent
I DO see the same with ZFS disks AND LVM disks being added&removed
=> not type dependent
I do NOT see the same on x86.
=> Arch dependent ??
... the evidence slowly points towards an issue in the guest, damn we are so
close to release - but non-fully detaching disks are critical in my POV :-/
Filing this as-is for awareness, but certainly this will need more debugging.
Unsure where this is going to eventually I'll now file it for kernel/udev/systemd.
If there are any known issues/components that are related let me know please!
---
ProblemType: Bug
AlsaDevices: Error: command ['ls', '-l', '/dev/snd/'] failed with exit code 2: ls: cannot access '/dev/snd/': No such file or directory
AplayDevices: Error: [Errno 2] No such file or directory: 'aplay'
ApportVersion: 2.20.11-0ubuntu65
Architecture: s390x
ArecordDevices: Error: [Errno 2] No such file or directory: 'arecord'
CRDA: N/A
CasperMD5CheckResult: unknown
DistroRelease: Ubuntu 21.04
IwConfig: Error: [Errno 2] No such file or directory: 'iwconfig'
Lspci:
Lspci-vt: -[0000:00]-
Lsusb: Error: command ['lsusb'] failed with exit code 1:
Lsusb-t: Error: command ['lsusb', '-t'] failed with exit code 1: /sys/bus/usb/devices: No such file or directory
Lsusb-v: Error: command ['lsusb', '-v'] failed with exit code 1:
Package: udev
PackageArchitecture: s390x
PciMultimedia:
ProcFB:
ProcKernelCmdLine: root=LABEL=cloudimg-rootfs
ProcVersionSignature: User Name 5.11.0-14.15-generic 5.11.12
RelatedPackageVersions:
linux-restricted-modules-5.11.0-14-generic N/A
linux-backports-modules-5.11.0-14-generic N/A
linux-firmware N/A
RfKill: Error: [Errno 2] No such file or directory: 'rfkill'
Tags: hirsute uec-images
Uname: Linux 5.11.0-14-generic s390x
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups: adm audio cdrom dialout dip floppy lxd netdev plugdev sudo video
_MarkForUpload: True
acpidump:
This bug is missing log files that will aid in diagnosing the problem. While running an Ubuntu kernel (not a mainline or third-party kernel) please enter the following command in a terminal window:
apport-collect 1925211
and then change the status of the bug to 'Confirmed'.
If, due to the nature of the issue you have encountered, you are unable to run this command, please add a comment stating that fact and change the bug status to 'Confirmed'.
This change has been made by an automated script, maintained by the Ubuntu Kernel Team.