Re: xenbus and the message of doom

[Konrad Rzeszutek Wilk <konrad@darnok.org>]

On Tue, Dec 20, 2011 at 02:15:33PM +0100, Olaf Hering wrote:
> On Tue, Dec 20, Ian Campbell wrote:
> 
> > What's wrong with only doing this reset if we know we are kexec'd? If
> > that can't be automatically detected then e.g. using an explicit
> > reset_watches command line option. You could even make a tenuous
> > argument for hanging this off reset_devices?
> 
> The kexec kernel does not know that it was loaded via kexec.
> We could make the reset_devices option mandatory for kexec in PVonHVM
> guests, so the change to drivers/xen/xenbus/xenbus_xs.c would be very
> small, like "if (hvm && reset_devices) xs_reset_watches();"

<nods> OK that would be one way. Granted if one tried to kexec under
Amazon EC2 an PVonHVM domain we would hit this bug again. But then
I don't think kexecing without this patch works, so that scenario is
probably moot.

> 
> > > Perhaps we should figure out what exactly EC2 is using as host and why
> > > it only breaks with upstream kernels.
> > 
> > and in the meantime we leave upstream (and any distros which picks up a
> > new enough kernel) on EC2? I think at this stage in the rc cycle we'd be
> > better off reverting and trying again for 3.3.
> 
> If EC2 is unable to fix it in time (or provide info what exactly they
> use), I'm ok with reverting/disabling the call to xs_reset_watches().

By my reckoning the 3.2 is going to come out Dec 29th (60 days after 3.1
was released) or it might slip. With folks buying presents online (and
potentially using Amazon) they [Amazon] is not going to fix anything -
they are in "must work now to sell stuff mode" - which means fix only
those $1M bugs. With the craze of purchases stopping around January I
think they could start addressing this sometime in Janurary - which would
be past the 3.2 release date.

Sorry Olaf, have to revert that commit.

> I can continue to work on this next year.

Ok. I need to serioulsy get a free Amazon EC2 instance to run nightly tests.
This is the third breakage this year.