[Bug 1925211] Re: Hot-unplug of disks leaves broken block devices around in Hirsute on s390x

[Seth Forshee]

The condition for css_sch_device_unregister(sch) also caught my eye,
calling it unconditionally is probably closer to right because it was
called in the !cdev case before, and in the attached patch it would no
longer be called in this case. However I think in the short term the
revert is the safest option, since the code will match what we already
know was working in the groovy kernel. Once a fix is committed upstream,
we can trade out the revert for that patch.

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Title:
  Hot-unplug of disks leaves broken block devices around in Hirsute on
  s390x

Status in Ubuntu on IBM z Systems:
  Triaged
Status in linux package in Ubuntu:
  Triaged
Status in systemd package in Ubuntu:
  Invalid
Status in udev package in Ubuntu:
  Invalid
Status in linux source package in Hirsute:
  Triaged
Status in systemd source package in Hirsute:
  Invalid
Status in udev source package in Hirsute:
  Invalid

Bug description:
  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 at hirsute-host
  on s390x

  I do NOT see the same with  groovy-guest at hirsute-host on s390x
  I DO see the same with hirsute-guest at 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:

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