[gentoo-user] Zombie Linux kernel

[gevisz <gevisz@gmail.com>]

I have not updated my Gentoo system since May 31, 2024,
so in the middle of October 2024 I had to install it anew.

Just to remind you: during that time we all had to switch
to the new Gentoo profile scheme, which made an update
from my old system more difficult than a new install.

During this new Gentoo install, I also moved
from ext4 to XFS for / and to ZFS for /home.

On October 26, I compiled a new Linux kernel.
It had version 6.6.52 and worked quite well.

However, with time it disappeared from the Gentoo portage tree.
So, 11 days ago I compiled kernel version 6.6.62 and successfully
booted my Gentoo system with it over the next 9 days.

The old kernel of version 6.6.52 was deleted from the /boot
directory just after compilation of kernel version 6.6.62 just
because it could not support my home ZFS disks any more
(because zfs-kmod should be compiled against the specific
kernel version and would not work with another one).

But yesterday, after booting my Gentoo system, the
uname -a
command reported that I have been booted with
the deleted old kernel version 6.6.52 compiled on October 26, 2024!
And, of course, it did not mount my ZFS /home.

An additional indication that it was the old kernel of version 6.6.52
was that the command lsmod showed that the XFS module was loaded,
while I had compiled it into the new kernel of version 6.6.62
no longer as a loadable module but as a part of the kernel itself.

I have double checked everything: the old kernel of version 6.6.52
together with its initramfs have been deleted from the /boot directory.
Moreover, just a day before I deleted /usr/lib/modules/6.6.52-gentoo/ directory.

I tried to reboot and found out that GRUB menu had only an option
of loading the old kernel of version 6.6.52.

However, I soon understood that the latter was because I have attached
additional HDD before booting my Gentoo system, and as a result of this
the system decided to boot from another HDD where I have not installed
a new GRUB file. So, I fixed it and my Gentoo system was finally able
to boot with the new kernel of version 6.6.62.

But the mystery of loading my Gentoo system with deleted kernel
and deleted modules remains. How could that happen at all?

My only explanation is that XFS actually had not deleted the old kernel
and the modules directory but only marked them as such. So, the old
GRUB file could load them even when they had been marked as deleted.
But is this explanation actually correct?