Re: xenbus and the message of doom

[Olaf Hering <olaf@aepfle.de>]

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
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