The "freezing while idle" problem does appear to be (at least) worked
around by the "Typical Current Idle" option.  If that counts as a fix,
then the bug is fixed -- or rather, was never a Kernel Bug.

The "Random Soft Lockup" -- the nominal subject of the bug -- on the
other hand... who can tell ?

It would be churlish not to be happy that my machine is now reliable and
I am a believer in credit where credit is due.

So, as you say, all credit goes to AMD for their total silence up to and
after the release of the work around (or fix) -- except for the advice
that some (older) power supplies might not work.  I don't really need to
know why or how the new option does the trick, but I remain curious
whether it has a material effect on power consumption.

But I also give credit to this bug's assignee for their total silence --
in particular:

  * it's not clear whether the "freezing while idle" and "Random Soft Lockup"
    problems are separate, related or the same.

  * hence, the CONFIG_RCU_NOCB_CPU and rcu_nocbs=0-15 voodoo may or may
    not still be recommended ?

    For all I know, with the "Typical Current Idle" option, I may be better
    off returning to the default configuration ?

  * and there is talk of kernel changes which reduce power consumption
    (significantly ?) -- which may or may not be related to these issues.

Sadly, the absence of solid information allows half-truths and ill-
informed speculation to take its place and to live on in the undamped
echo chamber of the interweb :-(  [I acknowledge my small part in that
noise :-(]

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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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