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

[Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>]

On Thu, Jan 05, 2012 at 09:41:26PM +0100, Olaf Hering wrote:
> Add 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.
> 
> With this change the xenstored is instructed to wipe all active watches
> for the guest.  However, a patch for xenstored is required so that it
> accepts the XS_RESET_WATCHES request from a client (see changeset
> 23839:42a45baf037d in xen-unstable.hg). Without the patch for xenstored
> the registration of watches will fail and some features of a PVonHVM
> guest are not available. The guest is still able to boot, but repeated
> kexec boots will fail.
> 
> Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>

Please resend and CC the maintainer and as well LKML.

> 
> ---
> 
> Note: the patch will be available via git://... once it was reviewed

huh?

> 
>  drivers/xen/xenbus/xenbus_xs.c     |   21 +++++++++++++++++++++
>  include/xen/interface/io/xs_wire.h |    3 ++-
>  2 files changed, 23 insertions(+), 1 deletion(-)
> 
> Index: linux-3.2/drivers/xen/xenbus/xenbus_xs.c
> ===================================================================
> --- linux-3.2.orig/drivers/xen/xenbus/xenbus_xs.c
> +++ linux-3.2/drivers/xen/xenbus/xenbus_xs.c
> @@ -621,6 +621,23 @@ static struct xenbus_watch *find_watch(c
>       return NULL;
>  }
>  
> +static void xs_reset_watches(void)
> +{
> +     int err, supported = 0;
> +
> +     if (!xen_hvm_domain())
> +             return;
> +
> +     err = xenbus_scanf(XBT_NIL, "control",
> +                     "platform-feature-xs_reset_watches", "%d", &supported);
> +     if (err != 1 || !supported)
> +             return;
> +
> +     err = xs_error(xs_single(XBT_NIL, XS_RESET_WATCHES, "", NULL));
> +     if (err && err != -EEXIST)
> +             printk(KERN_WARNING "xs_reset_watches failed: %d\n", err);
> +}
> +
>  /* Register callback to watch this node. */
>  int register_xenbus_watch(struct xenbus_watch *watch)
>  {
> @@ -897,5 +915,8 @@ int xs_init(void)
>       if (IS_ERR(task))
>               return PTR_ERR(task);
>  
> +     /* shutdown watches for kexec boot */
> +     xs_reset_watches();
> +
>       return 0;
>  }
> Index: linux-3.2/include/xen/interface/io/xs_wire.h
> ===================================================================
> --- linux-3.2.orig/include/xen/interface/io/xs_wire.h
> +++ linux-3.2/include/xen/interface/io/xs_wire.h
> @@ -29,7 +29,8 @@ enum xsd_sockmsg_type
>      XS_IS_DOMAIN_INTRODUCED,
>      XS_RESUME,
>      XS_SET_TARGET,
> -    XS_RESTRICT
> +    XS_RESTRICT,
> +    XS_RESET_WATCHES
>  };
>  
>  #define XS_WRITE_NONE "NONE"
> 
> _______________________________________________
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> Xen-devel@xxxxxxxxxxxxxxxxxxx
> http://lists.xensource.com/xen-devel

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