[Bug 1728760] Re: 17.04 to 17.10 dist upgrade switched me to lowlatency kernel b/c of aufs-tools

[Steve Langasek]

** Changed in: ubuntu-release-upgrader (Ubuntu)
       Status: Confirmed => Fix Committed

** Package changed: ubuntu-release-upgrader (Ubuntu) => aufs-tools
(Ubuntu)

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https://bugs.launchpad.net/bugs/1728760

Title:
  17.04 to 17.10 dist upgrade switched me to lowlatency kernel b/c of
  aufs-tools

Status in aufs-tools package in Ubuntu:
  Fix Committed
Status in aufs-tools source package in Artful:
  Fix Committed

Bug description:
  [SRU Justification]
  The combination in 17.10 of a new Recommends: on aufs-dkms from aufs-tools, with a new Provides: aufs-dkms on each of the kernel packages causes apt to choose a kernel at random to satisfy this package relationship on upgrade from 17.04.

  Randomly installing a kernel is bad mmmkay.

  [Test case]
  1. Install aufs-tools and linux-image-generic on a 17.04 system.
  2. Configure the apt sources to point to artful.
  3. Run sudo apt update && sudo apt dist-upgrade.
  4. Confirm that apt wants to install linux-image-4.13.0-16-lowlatency.
  5. Cancel the upgrade.
  6. Enable artful-proposed in sources.list.
  7. Run sudo apt update && sudo apt dist-upgrade.
  8. Confirm that apt no longer offers to install linux-image-4.13.0-16-lowlatency.

  [Regression potential]
  This will cause a behavior change in that currently, installing aufs-tools into a chroot or container will pull in a kernel package with it by default, and after this SRU it will no longer do so.

  This is not a regression.

  If a user is running a non-Ubuntu kernel which does not provide
  (explicitly or logically) aufs-dkms, after this SRU, installing aufs-
  tools will not cause an Ubuntu kernel package to be pulled in as a
  recommends.

  This is uninteresting, as the user would discover the lack of kernel
  aufs support the first time they tried to use the utilities; and it is
  unlikely that their preferred solution to the problem would be to stop
  using a non-Ubuntu kernel.

  
  [Original description]
  When I upgraded from 17.04 to 17.10, I was automatically switched from the generic kernel to the lowlatency kernel. I did not have the lowlatency kernel installed prior to the dist upgrade (I have verified this by inspecting my /var/log/apt/history.log* files, all upgrades prior to the dist upgrade only show updating *-generic kernel packages, if I had lowlatency installed it would show that as well.) I'm not sure why I was switched to lowlatency, I don't see anything in the release notes saying that there was a switch to lowlatency as the default, and other users who have just done a dist upgrade weren't switched to lowlatency. So I think it is probably a bug that I was switched to lowlatency - perhaps there's a package that I have installed that is incorrectly depending on the lowlatency kernel in 17.10? I'm not sure how to find out if that's the case.

  To be explicit, after the dist-upgrade, I had both the
  4.13.0-16-generic and 4.13.0-16-lowlatency kernels installed, and by
  default 4.13.0-16-lowlatency was what was booted into.

  This also caused a problem when I did the upgrade - perhaps this is a
  separate bug that I should report, let me know and I'll do that. After
  the dist-upgrade, wifi didn't work. I have a BCM4352 wifi card, whose
  driver is provided by the bcmwl-kernel-source package, which uses DKMS
  to compile it. Presumably during the dist-upgrade, the driver was
  compiled for the 4.13.0-16-generic kernel, so when I manually selected
  that kernel on boot, it worked, but it wasn't compiled for the
  4.13.0-16-lowlatency kernel, which is why wifi didn't work out of the
  box after the dist-upgrade. The solution was of course straight
  forward, I had to reinstall the bcmwl-kernel-source package, but a non
  working system after an upgrade requiring reinstalling packages or
  booting into a different kernel to fix is presumably a bug.

  If the switch from generic to lowlatency was a feature, not a bug,
  then such a switch should also be accompanied by compiling all the
  kernel modules that were compiled against the generic kernel against
  the new lowlatency kernel, so as to ensure the system is in a working
  state after completing a dist upgrade. Also, if the switch is a
  feature, then I would expect it to be documented in the release notes
  with a brief explanation or link to more information on why the switch
  was done.

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