[Bug 1877769] Update Released

[Łukasz Zemczak]

The verification of the Stable Release Update for unattended-upgrades
has completed successfully and the package is now being released to
-updates.  Subsequently, the Ubuntu Stable Release Updates Team is being
unsubscribed and will not receive messages about this bug report.  In
the event that you encounter a regression using the package from
-updates please report a new bug using ubuntu-bug and tag the bug report
regression-update so we can easily find any regressions.

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https://bugs.launchpad.net/bugs/1877769

Title:
  [SRU] Rewinding cache triggers obsolete adjustments consuming a lot of
  CPU

Status in unattended-upgrades package in Ubuntu:
  Fix Released
Status in unattended-upgrades source package in Focal:
  Fix Released
Status in unattended-upgrades package in Debian:
  Fix Released

Bug description:
  [Impact]

   * Unattended-upgrades consumes excessive amount of CPU when rewinding
  cache trying to mark packages to upgrade or install even when they are
  already marked to be upgraded or installed. This can be triggered by
  packages held back.

  [Test Case]

   * Run test_rewind.py:
     -Fixed output:
  $ python3 test_rewind.py 
  INFO:root:Allowed origins are: o=Ubuntu,a=lucid-security
  INFO:root:Initial blacklist: ant-doc
  INFO:root:Initial whitelist (not strict): 
  DEBUG:root:Marking not allowed <apt_pkg.PackageFile object: filename:'/home/rbalint/projects/deb/unattended-upgrades/test/root.rewind/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid-updates_main_binary-amd64_Packages'  a=lucid-updates,c=main,v=10.04,o=Ubuntu,l=Ubuntu arch='amd64' site='archive.ubuntu.com' IndexType='Debian Package Index' Size=894 ID:0> with -32768 pin
  DEBUG:root:Applying pinning: PkgFilePin(id=0, priority=-32768)
  DEBUG:root:Applying pin -32768 to package_file: <apt_pkg.PackageFile object: filename:'/home/rbalint/projects/deb/unattended-upgrades/test/root.rewind/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid-updates_main_binary-amd64_Packages'  a=lucid-updates,c=main,v=10.04,o=Ubuntu,l=Ubuntu arch='amd64' site='archive.ubuntu.com' IndexType='Debian Package Index' Size=894 ID:0>
  DEBUG:root:Applying pinning: PkgPin(pkg='/^ant-doc/', priority=-32768)
  DEBUG:root:APT::VersionedKernelPackages is not set
  DEBUG:root:adjusting candidate version: test-package=2.0
  DEBUG:root:adjusting candidate version: test2-package=2.0
  DEBUG:root:falling back to adjusting test2-package's dependencies
  DEBUG:root:falling back to adjusting z-package's dependencies
  DEBUG:root:sanity check failed for: set() : no package is selected to be upgraded or installed
  .
  ----------------------------------------------------------------------
  Ran 1 test in 0.022s

  OK

    - Not fixed output:
   $ python3 test_rewind.py 
  INFO:root:Allowed origins are: o=Ubuntu,a=lucid-security
  INFO:root:Initial blacklist: ant-doc
  INFO:root:Initial whitelist (not strict): 
  DEBUG:root:Marking not allowed <apt_pkg.PackageFile object: filename:'/home/rbalint/projects/deb/unattended-upgrades/test/root.rewind/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid-updates_main_binary-amd64_Packages'  a=lucid-updates,c=main,v=10.04,o=Ubuntu,l=Ubuntu arch='amd64' site='archive.ubuntu.com' IndexType='Debian Package Index' Size=894 ID:0> with -32768 pin
  DEBUG:root:Applying pinning: PkgFilePin(id=0, priority=-32768)
  DEBUG:root:Applying pin -32768 to package_file: <apt_pkg.PackageFile object: filename:'/home/rbalint/projects/deb/unattended-upgrades/test/root.rewind/var/lib/apt/lists/archive.ubuntu.com_ubuntu_dists_lucid-updates_main_binary-amd64_Packages'  a=lucid-updates,c=main,v=10.04,o=Ubuntu,l=Ubuntu arch='amd64' site='archive.ubuntu.com' IndexType='Debian Package Index' Size=894 ID:0>
  DEBUG:root:Applying pinning: PkgPin(pkg='/^ant-doc/', priority=-32768)
  DEBUG:root:APT::VersionedKernelPackages is not set
  DEBUG:root:adjusting candidate version: test-package=2.0
  DEBUG:root:adjusting candidate version: test2-package=2.0
  DEBUG:root:falling back to adjusting test2-package's dependencies
  DEBUG:root:falling back to adjusting z-package's dependencies
  DEBUG:root:sanity check failed for: set() : no package is selected to be upgraded or installed
  DEBUG:root:falling back to adjusting test-package's dependencies
  DEBUG:root:falling back to adjusting test2-package's dependencies
  DEBUG:root:falling back to adjusting test3-package's dependencies
  DEBUG:root:falling back to adjusting test-package's dependencies
  DEBUG:root:falling back to adjusting test2-package's dependencies
  DEBUG:root:falling back to adjusting test3-package's dependencies
  .
  ----------------------------------------------------------------------
  Ran 1 test in 0.024s

  (Note the extra "DEBUG:root:falling back to adjusting" ... lines)

  [Regression Potential]

   * Minimal. The very small change fixes how call_checked() verifies that the package to be upgrades/installed is indeed marked to either being installed or upgraded.
  In the worst case, if call_checked() erroneously returns success for a package as a result of a regression, unattended-upgrades does not fall back to adjusting packages to make marking successful. Later unattended-upgrades finds out that the package could not be marked and should be treated as kept back.

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