[Bug 1867786] Re: Qemu PPC64 freezes with multi-core CPU

[Laurent Vivier]

Thank you for the test. I'm going to try to reproduce the problem and
bisect.

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https://bugs.launchpad.net/bugs/1867786

Title:
  Qemu PPC64 freezes with multi-core CPU

Status in QEMU:
  New

Bug description:
  I installed Debian 10 on a Qemu PPC64 VM running with the following
  flags:

  qemu-system-ppc64 \
       -nographic -nodefaults -monitor pty -serial stdio \
       -M pseries -cpu POWER9 -smp cores=4,threads=1 -m 4G \
       -drive file=debian-ppc64el-qemu.qcow2,format=qcow2,if=virtio \
       -netdev user,id=network01,$ports -device rtl8139,netdev=network01 \

  
  Within a couple minutes on any operation (could be a Go application or simply 
changing the hostname with hostnamectl, the VM freezes and prints this on the 
console:

  ```
  root@debian:~# [  950.428255] rcu: INFO: rcu_sched self-detected stall on CPU
  [  950.428453] rcu:     3-....: (5318 ticks this GP) 
idle=8e2/1/0x4000000000000004 softirq=5957/5960 fqs=2544
  [  976.244481] watchdog: BUG: soft lockup - CPU#3 stuck for 23s! [zsh:462]

  Message from syslogd@debian at Mar 17 11:35:24 ...
   kernel:[  976.244481] watchdog: BUG: soft lockup - CPU#3 stuck for 23s! 
[zsh:462]
  [  980.110018] rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: 
{ 3-... } 5276 jiffies s: 93 root: 0x8/.
  [  980.111177] rcu: blocking rcu_node structures:
  [ 1013.442268] rcu: INFO: rcu_sched self-detected stall on CPU
  [ 1013.442365] rcu:     3-....: (21071 ticks this GP) 
idle=8e2/1/0x4000000000000004 softirq=5957/5960 fqs=9342
  ```

  If I change to 1 core on the command line, I haven't seen these
  freezes.

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