considering the complexity of Linux kernel it is expected to have many bugs. nothing to be scared about.
judge by results, not by advertisement. Did you had any kernel panics or shutdowns due to kernel bugs? Any bugs impacted your OS? there's 99% chance you'll say "NO".

Let me say yes here. I've definitely been impacted by kernel bugs, and not just one; and not only the ones of my own making.

my experience is a bit different. last time I encountered any issue is like 2008-2010 and kernel panics because of errors in implementation of Athlon CPU stepping. had no issues since then.

There actually is such a thing; it's called "User Mode Linux", but it's only availabe on x86 and x86_64; I really wish it were availabe for ARM, where hardware virtualization is often not availabe.

Of course, I think Linux might use something called "personalities" for this, or add new syscall numbers to the mix (as is done when the original syscall can't handle things like large files, or new flags need to be added).

Here's a bug I hit very recently: https://lkml.org/lkml/2019/1/4/62

Here's another: https://lore.kernel.org/patchwork/patch/950773/

There's been many more.

Soon, I'll probably need to be investigating an (unexpected, probably unintended) change in ip addr's behavior, most likely due to a new bug in kernel code...

I never hit these bugs because I'm on Debian 9 and it still uses old 4.9 kernel. by the time it will adopt 4.16 all these bugs will be patched. If you use latest kernels there's definitely trade-offs to that.

Yes, old kernels are not an option due to lacking hardware support.

could be :) why do you need latest kernel? be like M$ folks, install once per 10 years and never update it :)

Yep, exactly what i was meaning, though UML was more for debugging the kernel or playing around. But doing a package where UML runs, then talks to say X11 server to give you access to the current GUI while keeping all the bugs specifically for the one program, might just be what's needed.

Plus since it doesn't need all the drivers, 90% of the kernel can be stripped as API calls to the actual kernel for filesupport and other things, leaving for a very lightweight system.

I think i tinkered with UML back with 2.2.18, writing my own crypto cipher, incorporating it on a laptop. Was quite fun :)

Actually, buster (the new stable release) is on 4.19.

Heck. Fedora is on 5.1.17.

that's too new, I wonder if many bothered to upgrade. I haven't yet.

right, updated to Debian 10 just to feel the pain and sorrow. Nautilus dropped desktop icons support, Budgie new layout for panel looks ugly and counter-productive, timidity kicked in regression and takes hostage sound card (no sound till you kick it off - 1 year old bug and no action from timidity or Debian maintainers to keep old working version at least), my LAMP went defunct because this version of Debian have no phpmyadmin in repos and it looks php is also faulty, my scripts can't connect to database, some strange error issues on boot but I still try to figure out lamp issues. fkng awesome update, I'd better stayed on old kernel where everything worked flawlessly for a year.

That's why friends don't let friends use Debian.