Comment 2 for bug 1926440

I don't see any evidence that this is an issue with udev itself. Rather, udev upgrades cause update-initramfs to run, which triggers flash-kernel to generate u-boot-bootable files (uImage, uInitrd), which will also create a backup of the existing boot files (uImage->uImage.bak and uInitrd->uInitrd.bak) for recovery purposes. I'm guessing you have enough kernels installed that there just isn't room for these .bak files in /boot.

Some suggestions:
  1) Assuming you don't require a fallback kernel, remove /boot/uImage.bak and /boot/uInitrd.bak before installing new kernels. This will give flash-kernel more space to work with.
  2) If you have more than 2 kernels installed (current + next), try removing older kernels before installing new ones.
  3) Create a larger /boot partition.