group.of.nepali.translators team mailing list archive

[Joseph Salisbury <joseph.salisbury@xxxxxxxxxxxxx>]

** Also affects: linux (Ubuntu Xenial)
   Importance: Undecided
       Status: New

** Changed in: linux (Ubuntu Xenial)
       Status: New => In Progress

** Changed in: linux (Ubuntu Xenial)
   Importance: Undecided => Critical

** Changed in: linux (Ubuntu Xenial)
     Assignee: (unassigned) => Joseph Salisbury (jsalisbury)

** Changed in: linux (Ubuntu)
     Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage) => Joseph Salisbury (jsalisbury)

** Changed in: linux (Ubuntu)
       Status: Triaged => In Progress

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https://bugs.launchpad.net/bugs/1727331

Title:
  NMI watchdog: BUG: soft lockup on Guest upon boot (KVM)

Status in The Ubuntu-power-systems project:
  Triaged
Status in linux package in Ubuntu:
  In Progress
Status in linux source package in Xenial:
  In Progress

Bug description:
  Environment:
  Host OS: Ubuntu 16.04 (4.4.0-97-generic)
  Guest OS: Ubuntu 16.04 

  Host is running NovaLink and GPFS.  Guest gets filesystem from gpfs
  cluster.

  Issue:

  While booting the guest OS went into recovery.  dmesg shows CPU soft
  lockup.  This issue is easily recreatable when multiple VMs (about 10)
  are being started simultaneously.

  .......................................................................................................................

   - Paul Mackerras <pmac@xxxxxxxxxxx> - 2017-10-24 00:42:25 ==

  Looking at kernel sources:

  The Ubuntu host kernel (4.4.0-97) does not include the patch "KVM:
  PPC: Book3S: Treat VTB as a per-subcore register, not per-thread",
  which is commit 88b02cf97bb7 in the upstream Linux kernel repository.
  The symptom of not having this patch is that guests running with
  threads > 1 (that is, in SMT2, SMT4 or SMT8 mode) can give spurious
  soft-lockup messages when they are not in fact locked up, if the guest
  kernel uses the VTB (virtual timebase) register in its softlockup
  detector code.

  This is a backport of commit 88b02cf97bb7 from the upstream Linux
  kernel repository to the Ubuntu 4.4 kernel. It is the fix for the
  problem of seeing spurious soft lockup messages in guests running in
  an SMT mode greater than 1.

  These tests were run on a system with 20 cores.  Each VM had 1 core and 4 threads (SMT=4).
  It is working very well with this patch

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