Comment 0 for bug 1427075

== Comment: #0 - Cyril Bur <email address hidden> - 2015-02-23 18:03:41 ==
+++ This bug was initially created as a clone of Bug #108455 +++

I was investigating the cause of some ppc64le KVM guest softlockup warnings. On a single CPU KVM guest, I ran something to keep the guest busy:

yes > /dev/null &

Followed by

(qemu) stop

Wait a while, then:

(qemu) cont

We get a softlockup error:

BUG: soft lockup - CPU#0 stuck for 9220s! [yes:2389]

.__getnstimeofday
.getnstimeofday
.ktime_get_real
.netif_receive_skb
.ibmveth_poll
.net_rx_action
.__do_softirq
.irq_exit
.__do_irq
.call_do_irq
.do_IRQ

I was going to file it away in the "don't do that" bin, but I notice x86 have something to detect a paused VM and avoid spewing the soft lockup error. Do we need something like this on ppc64?

commit 5d1c0f4a80a6df73395fb3fc2c302510f8f09d36
Author: Eric B Munson <email address hidden>
Date: Sat Mar 10 14:37:28 2012 -0500

    watchdog: add check for suspended vm in softlockup detector

    A suspended VM can cause spurious soft lockup warnings. To avoid these, the
    watchdog now checks if the kernel knows it was stopped by the host and skips
    the warning if so. When the watchdog is reset successfully, clear the guest
    paused flag.

== Comment: #1 - Cyril Bur <email address hidden> - 2015-02-23 18:03:55 ==
Hi,

I have been working on a fix for guest kernels. This requires two patches:

1/2

commit 545a2bf742fb41f17d03486dd8a8c74ad511dec2
Author: Cyril Bur <email address hidden>
Date: Thu Feb 12 15:01:24 2015 -0800

    kernel/sched/clock.c: add another clock for use with the soft lockup watchdog

and 2/2

commit 4be1b29795d692d512bb67b770665d6f8ea5cb0b
Author: Cyril Bur <email address hidden>
Date: Thu Feb 12 15:01:28 2015 -0800

    powerpc: add running_clock for powerpc to prevent spurious softlockup warnings

Both are in upstream.