System fails to boot or hangs usually after a kernel upgrade

Issue

• After the initramfs has been rebuilt, which usually happens after a kernel upgrade, the system doesn't boot anymore and hangs in various places, as shown in the example below

  [...]
  [  OK  ] Started Journal Service.
  [*     ] A start job is running for dev-mapper-rootvg\x2droot.device (8h 33min 31s / no limit)
  

  In the example above, the root device cannot be mounted for some obscure reason.

  [  602.108396] INFO: task systemd-udevd:442 blocked for more than 120 seconds.
  [...]
  [  602.120763] Call Trace:
  [...]
  

  In the example above, systemd-udevd hangs, which is something not really expected.

• Monitoring the console during the boot, it may be possible to see oom-killer run, indicating a lack of memory

  [...]
  [   17.310507] Out of memory: Kill process 441 (systemd-udevd) score 0 or sacrifice child
  [...]
  

• Booting an older kernel doesn't solve the issue, indicating something is wrong in the real root file system