Re: [Xen-devel] xenbus and the message of doom

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Dec 16, 2011 at 12:33:00PM +0100, Olaf Hering wrote:
> On Thu, Dec 15, Konrad Rzeszutek Wilk wrote:
> 
> > On Thu, Dec 15, 2011 at 08:20:23PM +0100, Stefan Bader wrote:
> > > I was investigating a bug report[1] about newer kernels (>3.1) not 
> > > booting as
> > > HVM guests on Amazon EC2. For some reason git bisect did give the some 
> > > pain, but
> > > it lead me at least close and with some crash dump data I think I figured 
> > > the
> > > problem.
> > 
> > Stefan, thanks for finding this.
> > 
> > Olaf, what are your thoughts? Should I prep a patch to revert the patch
> > below and then we can work on 3.3 and rethink this in 3.3? The clock is
> > ticking for 3.2 and there is not much runway to fix stuff.
> 
> Sometimes guest changes expose bugs in the host. Its my understanding
> that hosts should be kept uptodate so that it can serve both old and new
> guests well.
> 
> In my testing with Xen4 based hosts their xenstored did properly ignore
> the new command.
> 
> I proposed several ways to get rid of existing watches, but finally we
> came to the conclusion that a new xenstored command would be the
> cleanest way.
> 
> Wether adding a timeout is a good idea has to be decided. I can imagine
> that a busy host may take some time to respond to guest commands.
> 
> 
> Perhaps we should figure out what exactly EC2 is using as host and why
> it only breaks with upstream kernels. So far I havent received reports

Good point. Stefan were you able to provide to Scott a kernel without the
git commit mentioned to see if that fixed the issue?

CC-ing here Vincent in hopes of getting some hints..

> for SLES11 guests. SP1 got an update recently, so their HVM guests would
> have seen the hang as well. The not yet released SP2 sends
> XS_RESET_WATCHES as well since quite some time.
> 
> 
> Olaf

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