I have tested it on 5.0 and still experienced the soft lockups just as 
frequently as with 4.20.
However, I am currently testing kernel 5.0 with PAGE_TABLE_ISOLATION disabled 
and it seems that it may be a fix.

Although maybe it's a bit premature to say that, since my experience with this 
issue (on 2700X) has been extremely inconsistent. I get the soft lockups, but 
in addition to the lockups (and usually preceding them) it seems like my whole 
system becomes unstable. Applications start segfaulting, or turning into 
zombies that can't be killed, then the lockup happens if I just let it go.
What's strange is that once this sort of "instability" occurs it seems to stay 
unstable even across reboots, and I can only have my machine running 20-30min 
before things start segfaulting or locking up again. Usually it takes me about 
5 or 6 restarts before it just seems to hit some sweet spot and become 
"stable". Once it's stable it stays stable for days, even if I restart the 
machine.

So based on the above description I can see that narrowing down the
problem could be very difficult since something might seem to be working
for a while, until it doesn't.

At any rate, the solution I'm currently testing was proposed in this Gentoo 
thread:
https://forums.gentoo.org/viewtopic-t-1074860-start-0.html
which I stumbled upon after receiving a kernel panic and noticing this error
>Unexpected reschedule of offline CPU#0!
>From what I can tell "offline CPU" sounds very relevant to our issue.

Their solution was to disable PAGE_TABLE_ISOLATION in the kernel. This also 
intrigues me as I remember seeing other errors in dmesg relating to "page" 
writing.
Apparently that kernel option isn't even necessary for AMD CPU's anyway. It was 
meant to fix an insecurity in intel CPU's, so it can be safely disabled.

NOTE: I am testing this with some of the BIOS modifications recommended by 
others here (such as disabling c6 state and "typical current idle", etc..)
If this solution works for another week or so I'll try restoring the BIOS 
settings to their defaults and testing again.

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https://bugs.launchpad.net/bugs/1690085

Title:
  Ryzen 1800X freeze - rcu_sched detected stalls on CPUs/tasks

Status in Linux:
  Confirmed
Status in linux package in Ubuntu:
  Confirmed

Bug description:
  Hi,

  
  We aregetting various kernel crash on a pretty new config.
  We're using Ryzen 1800X CPU with X370 Gaming Pro Carbon MB (7A32V1) using 
latest BIOS available (1.52)

  We are running Ubuntu 17.04 (amd64), we've tried different kernel version, 
native one and releases from http://kernel.ubuntu.com/~kernel-ppa/mainline/ too.
  Tested kernel version:

  native 17.04 kernel
  4.10.15

  Issues are the same, we're getting random freeze on the machine.

  Here is kern.log entry when happening :

  May 10 22:41:56 dev2 kernel: [24366.186246] INFO: rcu_sched detected stalls 
on CPUs/tasks:
  May 10 22:41:56 dev2 kernel: [24366.187618]     0-...: (1 GPs behind) 
idle=49b/1/0 softirq=28561/28563 fqs=913449
  May 10 22:41:56 dev2 kernel: [24366.188977]     (detected by 12, t=1860207 
jiffies, g=10001, c=10000, q=4656)
  May 10 22:41:56 dev2 kernel: [24366.190344] Task dump for CPU 0:
  May 10 22:41:56 dev2 kernel: [24366.190345] swapper/0       R  running task   
     0     0      0 0x00000008
  May 10 22:41:56 dev2 kernel: [24366.190348] Call Trace:
  May 10 22:41:56 dev2 kernel: [24366.190354]  ? native_safe_halt+0x6/0x10
  May 10 22:41:56 dev2 kernel: [24366.190355]  ? default_idle+0x20/0xd0
  May 10 22:41:56 dev2 kernel: [24366.190358]  ? arch_cpu_idle+0xf/0x20
  May 10 22:41:56 dev2 kernel: [24366.190360]  ? default_idle_call+0x23/0x30
  May 10 22:41:56 dev2 kernel: [24366.190362]  ? do_idle+0x16f/0x200
  May 10 22:41:56 dev2 kernel: [24366.190364]  ? cpu_startup_entry+0x71/0x80
  May 10 22:41:56 dev2 kernel: [24366.190366]  ? rest_init+0x77/0x80
  May 10 22:41:56 dev2 kernel: [24366.190368]  ? start_kernel+0x464/0x485
  May 10 22:41:56 dev2 kernel: [24366.190369]  ? 
early_idt_handler_array+0x120/0x120
  May 10 22:41:56 dev2 kernel: [24366.190371]  ? 
x86_64_start_reservations+0x24/0x26
  May 10 22:41:56 dev2 kernel: [24366.190372]  ? x86_64_start_kernel+0x14d/0x170
  May 10 22:41:56 dev2 kernel: [24366.190373]  ? start_cpu+0x14/0x14
  May 10 22:44:56 dev2 kernel: [24546.188093] INFO: rcu_sched detected stalls 
on CPUs/tasks:
  May 10 22:44:56 dev2 kernel: [24546.189461]     0-...: (1 GPs behind) 
idle=49b/1/0 softirq=28561/28563 fqs=935027
  May 10 22:44:56 dev2 kernel: [24546.190823]     (detected by 14, t=1905212 
jiffies, g=10001, c=10000, q=4740)
  May 10 22:44:56 dev2 kernel: [24546.192191] Task dump for CPU 0:
  May 10 22:44:56 dev2 kernel: [24546.192192] swapper/0       R  running task   
     0     0      0 0x00000008
  May 10 22:44:56 dev2 kernel: [24546.192195] Call Trace:
  May 10 22:44:56 dev2 kernel: [24546.192199]  ? native_safe_halt+0x6/0x10
  May 10 22:44:56 dev2 kernel: [24546.192201]  ? default_idle+0x20/0xd0
  May 10 22:44:56 dev2 kernel: [24546.192203]  ? arch_cpu_idle+0xf/0x20
  May 10 22:44:56 dev2 kernel: [24546.192204]  ? default_idle_call+0x23/0x30
  May 10 22:44:56 dev2 kernel: [24546.192206]  ? do_idle+0x16f/0x200
  May 10 22:44:56 dev2 kernel: [24546.192208]  ? cpu_startup_entry+0x71/0x80
  May 10 22:44:56 dev2 kernel: [24546.192210]  ? rest_init+0x77/0x80
  May 10 22:44:56 dev2 kernel: [24546.192211]  ? start_kernel+0x464/0x485
  May 10 22:44:56 dev2 kernel: [24546.192213]  ? 
early_idt_handler_array+0x120/0x120
  May 10 22:44:56 dev2 kernel: [24546.192214]  ? 
x86_64_start_reservations+0x24/0x26
  May 10 22:44:56 dev2 kernel: [24546.192215]  ? x86_64_start_kernel+0x14d/0x170
  May 10 22:44:56 dev2 kernel: [24546.192217]  ? start_cpu+0x14/0x14

  Depending on the kernel version, we've got NMI watchdog errors related to CPU 
stuck (mentioning the CPU core id, which is random).
  Crash is happening randomly, but in general after some hours (3-4h).

  Now, we've installed kernel 4.11.0-041100-generic #201705041534 this morning 
and waiting for crash...
  For now, the machine is not "used", at least, it's not CPU stressed...

  
  Thanks
  --- 
  ApportVersion: 2.20.4-0ubuntu4
  Architecture: amd64
  DistroRelease: Ubuntu 17.04
  InstallationDate: Installed on 2017-05-09 (1 days ago)
  InstallationMedia: Ubuntu-Server 17.04 "Zesty Zapus" - Release amd64 
(20170412)
  Package: linux (not installed)
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=fr_FR.UTF-8
   SHELL=/bin/bash
  Tags:  zesty
  Uname: Linux 4.11.0-041100-generic x86_64
  UnreportableReason: The running kernel is not an Ubuntu kernel
  UpgradeStatus: No upgrade log present (probably fresh install)
  UserGroups:
   
  _MarkForUpload: True

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