** 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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Matching subscriptions: Ubuntu 16.04 Bugs
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 <p...@au1.ibm.com> - 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
To manage notifications about this bug go to:
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