[Bug 2034510] Re: spl fails to unregister sysctl entries

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https://bugs.launchpad.net/bugs/2034510

Title:
  spl fails to unregister sysctl entries

Status in zfs-linux package in Ubuntu:
  New
Status in zfs-linux source package in Mantic:
  New

Bug description:
  [Impact]

  On unload the spl module is not properly cleaning up the registered
  sysctl entries with kernel 6.5 in Mantic:

  06:58 ubuntu at mantic$ sudo modprobe spl
  modprobe: ERROR: could not insert 'spl': Protocol driver not attached
  06:58 ubuntu at mantic$ sudo dmesg | grep duplicate
  [  152.587197] sysctl duplicate entry: /kernel/spl/kmem/slab_kvmem_total

  [Test case]

  Uninstall zfsutils-linux and try to `modprobe -r zfs; modprobe -r
  spl`, then `modprobe zfs` again and you should see the error (with a
  failure to load spl again).

  At this point it is possible to load spl again only after a reboot.

  [Fix]

  Properly cleanup all the registered sysctl entries when the spl module
  is unloaded.

  [Regression potential]

  We may experience regressions in systems that are using zfs with the
  6.5 kernel.

  ProblemType: Bug
  DistroRelease: Ubuntu 23.10
  Package: zfs-dkms 2.2.0~rc3-0ubuntu3
  ProcVersionSignature: User Name 6.5.0-4.4-generic 6.5.0
  Uname: Linux 6.5.0-4-generic x86_64
  ApportVersion: 2.27.0-0ubuntu2
  Architecture: amd64
  CasperMD5CheckResult: unknown
  CloudArchitecture: x86_64
  CloudBuildName: server
  CloudID: nocloud
  CloudName: unknown
  CloudPlatform: nocloud
  CloudSerial: 20230823
  CloudSubPlatform: config-disk (/dev/vdb)
  Date: Wed Sep  6 07:06:33 2023
  PackageArchitecture: all
  ProcEnviron:
   LANG=C.UTF-8
   PATH=(custom, no user)
   SHELL=/bin/bash
   TERM=xterm-256color
   XDG_RUNTIME_DIR=<set>
  SourcePackage: zfs-linux
  UpgradeStatus: No upgrade log present (probably fresh install)

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