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

On Mon, Aug 15, 2011 at 02:59:58PM +0200, Olaf Hering wrote:
> 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?

commit 6b71c52e7f848e2c9f804e175215e5965ea90d32
Author: Olaf Hering <olaf@xxxxxxxxx>
Date:   Thu Jul 28 15:23:03 2011 +0200

    xen: use static initializers in xen-balloon.c
    There is no need to use dynamic initializaion, it just confuses the reader.
    Switch to static initializers like its used in other files.
    Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
    [v2: Rebased on v3.0]

> > 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

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