Re: [PATCH] xen/pv-on-hvm kexec: add xs_reset_watches to shutdown watches from old kernel

[Olaf Hering <olaf@aepfle.de>]

On Mon, Aug 15, Konrad Rzeszutek Wilk wrote:

> On Mon, Aug 15, 2011 at 11:25:30AM +0200, Olaf Hering wrote:
> > Add new xs_reset_watches function to shutdown watches from old kernel after
> > kexec boot.  The old kernel does not unregister all watches in the
> > shutdown path.  They are still active, the double registration can not
> > be detected by the new kernel.  When the watches fire, unexpected events
> > will arrive and the xenwatch thread will crash (jumps to NULL).  An
> > orderly reboot of a hvm guest will destroy the entire guest with all its
> > resources (including the watches) before it is rebuilt from scratch, so
> > the missing unregister is not an issue in that case.
> 
> So this patch replaces the big patch series you sent some while ago?
> [I've one of your patches in my tree, but I wasn't sure about the other
> ones]

No, there are 3 other patches required:

xen/pv-on-hvm kexec+kdump: reset PV devices in kexec or crash kernel
xen/pv-on-hvm kexec: rebind virqs to existing eventchannel ports
xen/pv-on-hvm kexec: prevent crash in xenwatch_thread() when stale watch events arrive

I will send them once we settled on a way to reset the watches.

Which one did you already apply?

> If the xenstore does not have the patch for this, what is the
> error code? Is it ENOSYS? If we get that can we not print this message?
> Or perhaps print:
> "Yikes! We can't reset the watches. Potential crash immienient"
> or something similar.

Now that you mention it, the return code should be checked and ENOSYS
should be filtered to not print the warning on a host without the
updated xenstored.  I will update that part of the patch.

Olaf