Mine is fine now with BIOS update

I applied a BIOS update which seem to fix the issue for the first few days until the lockup occurred again. I then applied another update that had become available in the meantime which made the problem much worse. Interestingly, on my motherboard, this update was supposed to improve Threadripper power management, and the impact on my system was drastic: reboots started causing kernel panics, and the system would lock up within minutes after boot.
I've since booted off a newer kernel and have been stable for about 12h now.

Inspite of patching, my lockups persist, about once every two weeks. Since this is a desktop (not server) machine I've decided to just live with it.

I'm still waiting for AMD to get back to me on this. I've written to them requesting support. I even heard that AMD, in the past also did a recall of some Ryzen CPU's due to a hardware bug that couldn't be patched. I've however, not found any way to know if my particular CPU is also affected.

If all fails, I guess I'd want to replace my 2950x with something from Intel. Intel based hardware, in my opinion tends to be more stable on linux.

In. my 20 years of using Linux and/or a BSD, I have never once had a problem with an Intel CPU. I have been interested in the AMD offerings, but am still not going to jump ship because I don't think there is any benefit for me. Perhaps one day.

IMO, the benefit to AMD was $$. I got a Ryzen 1700x because for 8 cores/16 threads, I spent less than 1/2 what Intel would cost.
I replaced it with a 3700x because for 8 cores/16 threads, I spend about 3/4 what Intel would cost.
AMD has almost always been the "value" buy. Generally their processors aren't as good as Intel (although currently outside mobile they crush Intel at everything except pure gaming), but they've usually delivered a much better value for your $$.
I've always purchased whoever offered the best bang for the $$. I've had Intel, I've had AMD. AT this moment in time, if i was purchasing a desktop/workstation/server, I wouldn't actively consider Intel. The chips are less powerful but still cost more. Buying mobile it comes down to price. The Intel chips are hands down simply better than anything AMD has released, but there's some SMOKING deals on AMD laptops!!!
As to reliability, I've had DOA Intel chips, I've had DOA AMD chips. I've had INtel chips with flaws, I've had AMD chips with flaws. Neither has been perfect. Both companies have shipped garbage, both companies have shipped amazing processors that hit so far above their price point it's amazing (I still have fond memories of the Celeron A 450...errrr 300, not that ANYONE ran it at 300). In the end, not a fanboy of either, I buy whoever saves me $$$ for the level of performance I can afford.

Good points. I am not ruling AMD out, I just wouldn't go bleeding edge and crazy-fast (Thread ripper?). I just built this Intel system about 2 years ago though so not in a hurry to upgrade. It should last a good long time. I will consider AMD next time though. Already looking at AMD video cards because my poor little Intel HD630, although mostly fine, chokes on some games I like.

I'm running a threadripper machine and I use this for really heavy build workloads: I need that kind of performance since I'm into compiling large programs in languages that are usually expensive to compile. I initially went for the TR since it promised to be great value for money and it was offering me the kind of horsepower I needed at a much better price than Intel. But trust me, in the end what counts is a stable system. No matter how powerful your system is, if it is unstable, it is almost useless. I now use this machine with crashes always at the back of my mind: I tend to save files more often, which, admittedly I consider a distraction.
In my opinion, if I were to buy a system today after experiencing this system for a year, I'd happily trade in some of the horsepower for a rock solid system, which one gets from Intel on Linux at least.
I also have an Intel based thinkpad, which has now been up for months with zero surprises whatsoever.

I wouldn't consider Threadripper ONLY because the chips ALONE prices START at about $200 under what I generally pay for an ENTIRE SYSTEM. I'd love to be able to afford a Threadripper, but I like to upgrade fairly regularly, and I just don't MAKE ENOUGH to do Threadripper.

Once I got the balance of boot parameters and disabled c6 states (zenstates.py), mine's been rock solid. I can't speak to the Threadrippers, since they're out of my pricerange. (When I built this computer, my old one suddenly died, so I had to replace it and still be able to pay the rent.)

I've just stuck with my rcu-nocbs option in my kernel appends. I know that others have had their problems solved with BIOS/firmware updates, but at some point after I read that, I ensured my firmware was the latest version, removed that option, and I still had occasional lockups. My issue might've been solved with updates since that point, but I'm too lazy to test it at the risk of locking up my machine. I'm not aware of any downsides that using that option might cause, so I'll continue to use it as a security blanket.

I just sold my 12 core Xeon monster because it was old and I rarely use it. My "new" i7 7700 does just fine on builds: I can build about 800 FreeBSD packages in 4-5 hours. Not bad and I just do it overnight once a week. The HP z800 could the same thing in 1-3 hours but also was loud, hot and sucked massive amounts of electricity.

I would consider an AMD next build that is equivalent to whatever a semi modern Intel CPU is. I'd have to research chips to learn about them though: haven't had an AMD CPU since the K5 days...I think that was model.

So AMD was decently prompt in responding to my support request but far from helpful. Their fix to this issue is to disable C6 in your BIOS. This is 2020, and a high end processor that costs close to $1000 (at the time of buying), and the vendor advises to disable power management to make a system as expensive behave acceptably.
Needless to say, at this point I'm desperate enough to try anything to make the desktop work decently, so I'll take their advice. But I'm keeping away from AMD for the time being for all new hardware investment for the foreseeable future.

It's issues like these that make me glad I held off upgrading to a Ryzen. My vintage (and venerable) FX-8370 processor may be considered ancient junk by a lot of people, but at least I don't have to resort to kludgy workarounds to make my system perform as intended. Everything "just works". As an added bonus, it is more than capable of handling the newest incarnation of DOOM just fine (and everything else I throw at it), even though the system specs state that Ryzen 3 is the minimum. Fancy that! And on ultra settings, I get upwards of 60 fps at 1440p! For the record, my RAM (32 GB) and graphics card (RX 580) exceed minimum spec.

Interesting. I just priced out an AMD build (motherboard and CPU), I think gigabyte and a Ryzen 5 3600, and the price difference from my i7 7700 was about $100, but the Ryzen 5 has more cores and I think it equivalent to a newer gen Intel. Not entirely sure on that. For me, there is very little return on investment so I am not in a hurry to change from Intel to AMD. I didn't even consider it for this last build because one of my kids gave me a new Intel based motherboard for Christmas a couple of years ago so my choice was made