Re: [Qemu-devel] [PATCH 1/1] kvmclock: fix guest stop notification

[Amit Shah]

On (Sun) 30 Sep 2012 [21:50:07], Amos Kong wrote:
> ----- Original Message -----
> > On Thu, Sep 20, 2012 at 09:46:41AM -0300, Marcelo Tosatti wrote:
> > > On Thu, Sep 20, 2012 at 01:55:20PM +0530, Amit Shah wrote:
> > > > Commit f349c12c0434e29c79ecde89029320c4002f7253 added the guest
> > > > stop
> 
> In commitlog of f349c12c0434e29c79ecde89029320c4002f7253: 
> 
> ## This patch uses the qemu Notifier system to tell the guest it _is about to 
> be_ stopped
> 
> 
> > > > notification, but it did it in a way that the stop notification
> > > > would
> > > > never reach the kernel.  The kvm_vm_state_changed() function gets
> > > > a
> > > > value of 0 for the 'running' parameter when the VM is stopped,
> > > > making
> > > > all the code added previously dead code.
> > > > 
> > > > This patch reworks the code so that it's called when 'running' is
> > > > 0,
> > > > which indicates the VM was stopped.
> 
> Amit, did you touch any real issue? guest gets call trace with current code?
> which kind of context?

I guess you're asking for a testcase to trigger softlockups?

Run a VM, make it do some work (like kernel compile).  Then, 'stop'
from the monitor for a few minutes.  Later, on 'cont', the softlockup
detector in the guest wakes up and shows a warning message mentioning
the cpus were stuck for <n> seconds.

For this particular patch, though, I didn't really test things; just
'found' this by examining code.  But as Marcelo points out, this patch
is wrong.

> Someone told me he got call trace when shutdown guest by 'init 0', I didn't
> verify this issue.

That sounds like a completely different thing, unless the trace is
invoked by the softlockup detector.

                Amit