[Bug 1969365] Re: focal: backport kexec fallback patch

[Dan Watkins]

In the VM created in my above comment, I enabled proposed, installed the
new systemd and rebooted.  After that, I re-ran:

cd /boot
sudo kexec -l vmlinuz --initrd initrd.img --append 'BOOT_IMAGE=/boot/vmlinuz-5.4.0-167-generic root=LABEL=cloudimg-rootfs ro console=tty1 console=ttyS0'
sudo reboot

And observed the following in the console:

[  OK  ] Reached target Final Step.
         Starting Reboot via kexec...
[  102.782246] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [960] did not accept message, killing the worker: Connection refused
[  102.784224] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [963] did not accept message, killing the worker: Connection refused
[  102.786398] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [966] did not accept message, killing the worker: Connection refused
[  102.788390] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [968] did not accept message, killing the worker: Connection refused
[  102.789954] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [962] did not accept message, killing the worker: Connection refused
[  102.791562] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [961] did not accept message, killing the worker: Connection refused
[  102.793198] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [964] did not accept message, killing the worker: Connection refused
[  102.794669] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [967] did not accept message, killing the worker: Connection refused
[  102.796841] systemd-udevd[369]: anon_vma(937:udisks2.service): Worker [965] did not accept message, killing the worker: Connection refused
[  102.904092] kexec_core: Starting new kernel
[    0.000000] Linux version 5.4.0-167-generic (buildd at lcy02-amd64-010) (gcc version 9.4.0 (Ubuntu 9.4.0-1ubuntu1~20.04.2)) #184-Ubuntu SMP Tue Oct 31 09:21:49 UTC 2023 (Ubuntu 5.4.0-167.184-generic 5.4.252)

So I can confirm that the new systemd addresses this bug.

** Tags removed: verification-needed-focal
** Tags added: verification-done-focal

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https://bugs.launchpad.net/bugs/1969365

Title:
  focal: backport kexec fallback patch

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Focal:
  Fix Committed

Bug description:
  It would be great if focal's systemd could have
  https://github.com/systemd/systemd/commit/71180f8e57f8fbb55978b00a13990c79093ff7b3
  backported to it.

  [Impact]

  We have observed that kexec'ing to another kernel will fail as the
  drive containing the `kexec` binary has been unmounted by the time
  systemd attempts to do so, indicated in the console:

           Starting Reboot via kexec...
  [  163.960938] shutdown[1]: (sd-kexec) failed with exit status 1.
  [  163.963463] reboot: Restarting system

  [Test Plan]

  1) Launch a 20.04 instance
  2) `apt-get install kexec-tools`
  3) In `/boot`, filling in whatever <cmdline> needed in your environment:

  kexec -l vmlinuz --initrd initrd.img --append '<cmdline>'

  4) `reboot`

  (I have reproduced this in a single-disk VM, so I assume it reproduces
  ~everywhere: if not, `apt-get remove kexec-tools` before the `reboot`
  could be used to emulate the unmounting.)

  [Where problems could occur]

  Users could inadvertently be relying on the current behaviour: if they
  have configured their systems to kexec, they currently will be
  rebooting normally, and this patch would cause them to start actually
  kexec'ing.

  [Other info]

  We're currently maintaining a systemd tree with only this patch added
  to focal's tree: this patch has received a bunch of testing from us in
  focal.

  This patch landed in v246, so it's already present in supported
  releases later than focal.

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