[Bug 1782094] Re: pkgstripfiles: symlinking docs and optimizing pngs/trucating changelogs in parallel produces undeterministic results

[Robie Basak]

Hello Balint, or anyone else affected,

Accepted pkgbinarymangler into bionic-proposed. The package will build
now and be available at
https://launchpad.net/ubuntu/+source/pkgbinarymangler/138.18.04.0 in a
few hours, and then in the -proposed repository.

Please help us by testing this new package.  See
https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how
to enable and use -proposed.Your feedback will aid us getting this
update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug,
mentioning the version of the package you tested and change the tag from
verification-needed-bionic to verification-done-bionic. If it does not
fix the bug for you, please add a comment stating that, and change the
tag to verification-failed-bionic. In either case, details of your
testing will help us make a better decision.

Further information regarding the verification process can be found at
https://wiki.ubuntu.com/QATeam/PerformingSRUVerification .  Thank you in
advance!

** Changed in: pkgbinarymangler (Ubuntu Bionic)
       Status: New => Fix Committed

** Tags added: verification-needed verification-needed-bionic

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https://bugs.launchpad.net/bugs/1782094

Title:
  pkgstripfiles: symlinking docs and optimizing pngs/trucating
  changelogs  in parallel produces undeterministic results

Status in pkgbinarymangler package in Ubuntu:
  Fix Released
Status in pkgbinarymangler source package in Bionic:
  Fix Committed

Bug description:
  [Impact]

   * PNG optimization and changelog truncation can happen in parallel with symlinking docs across packages. When checking for duplicates files the duplicate check may compare the processed files with non-processed ones and in that case they are found to be different despite the processed (or the unprocessed) files would be identical. The resulting binary packages would be still valid, but may be different for different architectures since the parallel build process may hit this race condition when processing different files making the arch:any packages not coinstallable on a multiarch-enabled system.
   * One manifestation of the problem can be seen in https://launchpadlibrarian.net/355140796/buildlog_ubuntu-bionic-i386.gpm_1.20.7-5_BUILDING.txt.gz where symlinking's file comparison occurs while truncating the changelog:
  ...
  Searching for duplicated docs in dependency libgpm2...
  pkgstripfiles: Truncating usr/share/doc/libgpm2/changelog.Debian.gz to topmost ten records

  gzip: /<<PKGBUILDDIR>>/debian/libgpm-dev/../libgpm2/usr/share/doc/libgpm2/changelog.Debian.gz: unexpected end of file
  cmp: EOF on /dev/fd/62 which is empty
  ...

   * The fix is protecting png optimization and trucating changelogs
  with the same lock as used to serialize doc symlinking thus those
  steps are serialized as well. The fix also skips optimizing PNGs and
  truncating changelogs of dbgsym files in pkgstripfiles.

  [Test Case]

   * Build an affected package (like gpm) for i386 and amd64 with fixed pkgbinarymangler and observe the files in /usr/share/doc in the built packages to be identical and there should be no line like the following in the build log:
  gzip: /<<PKGBUILDDIR>>/debian/libgpm-dev/../libgpm2/usr/share/doc/libgpm2/changelog.Debian.gz: unexpected end of file
   * Note that due to the non-deterministic nature of the failure several builds could be necessary to reproduce the original problem and also for verifying that the problem is fixed. You can increase the chances of observing the failure by building the packages with higher level of parallelism (-jX).

  [Regression Potential]

   * Due to serialization the build times may increase for packages where the serialized steps ran in parallel originally. IMO there is not much we can do about that apart from trying to speed up the steps themselves.
   * Since no additional locks were introduced I believe the builds won't break or stall due to this change.
   * The fix also skips optimizing PNGs and truncating changelogs of dbgsym files, but PNG files are typically not present there and /usr/share/doc/<pkg>-dbgsym is symlinked to /usr/share/doc/<pkg> even with the fix thus the change of pkgstripfiles does not have an effect on the built dbgsym files' changelogs.

  [Other Info]

   * There are some packages which need to be rebuilt with the updated
  pkgbinarymangler, collecting them is in progress.

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