[Bug 2007827] Re: [SRU] flash-kernel failure when upgrading f-k and kernel in the same cycle

[Steve Langasek]

Dave, I don't agree that there's a relevant difference here between
flash-kernel and grub.

Grub: initrd not yet generated; grub postinst is called and adds kernel
as first entry in grub.cfg; power event happens before kernel postinst
is called; system fails to (noninteractively) boot.

flash-kernel: initrd not yet generated; flash-kernel postinst is called
and writes kernel (without initramfs) to the boot partition; power event
happens before kernel postinst is called; system fails to boot.

Both scenarios need to be guarded against, and we should use the same
model for both (and any other bootloaders on other archs).

*Unfortunately*, it turns out that while Andy and I whiteboarded this
about 5 years back, what we discussed never wound up being implemented
in the kernel packages.  I believe the plan at the time was to use a
dpkg-divert in the kernel preinst to divert /boot/vmlinuz-$ver to
/boot/vmlinuz-$ver.dpkg-something, and then to un-divert it in the
postinst only after the initramfs has been generated.  grub already has
code to ignore the pattern vmlinuz*.dpkg-* so no further changes would
be required for grub; and it would be easy to make flash-kernel match.

However, none of this matters so long as the kernel doesn't implement
such an interface.

In any case, I'm not happy with the proposed implementation in flash-
kernel.  I think rooting around in the dpkg database is bad form.
Ultimately, though, it's not my opinion on this that matters - we really
need input from the Kernel Team here wrt what interface we're going to
support between the packages.  I subscribed Andy to the bug, but he
hasn't replied yet; adding Dimitri as well.

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https://bugs.launchpad.net/bugs/2007827

Title:
  [SRU] flash-kernel failure when upgrading f-k and kernel in the same
  cycle

Status in flash-kernel package in Ubuntu:
  Fix Released
Status in flash-kernel source package in Focal:
  New
Status in flash-kernel source package in Jammy:
  New
Status in flash-kernel source package in Kinetic:
  Incomplete
Status in flash-kernel source package in Lunar:
  Fix Released

Bug description:
  [Impact]
  In version 3.104ubuntu15 of flash-kernel, when both f-k and the kernel are upgraded in the same cycle, depending on the ordering of dpkg trigger execution, f-k may find the content of /boot "inconsistent" causing it to fail and return error exit status 1.

  Erorr message:
  Processing triggers for man-db (2.10.2-1) ...
  Processing triggers for flash-kernel (3.104ubuntu15) ...
  flash-kernel: installing version 5.15.0-1018-xilinx-zynqmp
  Initrd required for FIT method
  dpkg: error processing package flash-kernel (--configure):
   installed flash-kernel package post-installation script subprocess returned error exit status 1
  Processing triggers for linux-image-5.15.0-1018-xilinx-zynqmp (5.15.0-1018.20) ...
  /etc/kernel/postinst.d/initramfs-tools:
  update-initramfs: Generating /boot/initrd.img-5.15.0-1018-xilinx-zynqmp

  flash-kernel gets the latest kernel version by "linux-version list".
  When flash-kernel was triggered to generate fitimage, the kernel version is "5.15.0-1018" and the initrd for it wasn't ready. So, flash-kernel failed to generate the fitimage.

  A subsequent run of "apt install -f" fixed things because, by that
  point, the kernel's own trigger had executed, ensuring that update-
  initramfs had been run. In the case that f-k is run "prematurely" and
  finds itself in this situation (/boot/kernel-$[ver} exists, but
  /boot/initrd-${ver}) doesn't), it should probably bail out silently
  under the assumption that whatever is responsible for it will rectify
  the situation and trigger f-k again (as happens in the kernel postinst
  hooks).

  [Test Case]
  1. Flash an old image (with an out of date kernel and flash-kernel)
  2. sudo apt-get update
  3. sudo apt install flash-kernel with the fix and linux packages
  4. Upgrade should proceed without issue

  [Regression Potential]
  As with the previous flash-kernel uploads, it is possible that a breakage in the changed code can lead to issues with upgrading kernels (due to f-k being executed via a trigger at the end) or with Xilinx devices in the field not upgrading correctly. I will test all the changes extensively though.

  Related issues:
  LP: #1861292 flash-kernel failure during kernel upgrade

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