Re: qemu-system-ppc64 abort()s with pcie bridges

[Greg Kurz <groug@kaod.org>]

On Wed, 8 Jul 2020 10:03:47 +0200
Thomas Huth <thuth@redhat.com> wrote:

> 
>  Hi,
> 
> qemu-system-ppc64 currently abort()s when it is started with a pcie
> bridge device:
> 
> $ qemu-system-ppc64 -M pseries-5.1 -device pcie-pci-bridge
> Unexpected error in object_property_find() at qom/object.c:1240:
> qemu-system-ppc64: -device pcie-pci-bridge: Property '.chassis_nr' not found
> Aborted (core dumped)
> 
> or:
> 
> $ qemu-system-ppc64 -M pseries -device dec-21154-p2p-bridge
> Unexpected error in object_property_find() at qom/object.c:1240:
> qemu-system-ppc64: -device dec-21154-p2p-bridge: Property '.chassis_nr'
> not found
> Aborted (core dumped)
> 
> That's kind of ugly, and it shows up as error when running
> scripts/device-crash-test. Is there an easy way to avoid the abort() and
> fail more gracefully here?
> 

And even worse, this can tear down a running guest with hotplug :\

(qemu) device_add pcie-pci-bridge 
Unexpected error in object_property_find() at /home/greg/Work/qemu/qemu-ppc/qom/object.c:1240:
Property '.chassis_nr' not found
Aborted (core dumped)

This is caused by recent commit:

commit 7ef1553dac8ef8dbe547b58d7420461a16be0eeb
Author: Markus Armbruster <armbru@redhat.com>
Date:   Tue May 5 17:29:25 2020 +0200

    spapr_pci: Drop some dead error handling
    
    chassis_from_bus() uses object_property_get_uint() to get property
    "chassis_nr" of the bridge device.  Failure would be a programming
    error.  Pass &error_abort, and simplify its callers.
    
    Cc: David Gibson <david@gibson.dropbear.id.au>
    Cc: qemu-ppc@nongnu.org
    Signed-off-by: Markus Armbruster <armbru@redhat.com>
    Acked-by: David Gibson <david@gibson.dropbear.id.au>
    Reviewed-by: Greg Kurz <groug@kaod.org>
    Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
    Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
    Message-Id: <20200505152926.18877-18-armbru@redhat.com>

Before that, we would simply print the "chassir_nr not found" error,
and in case of a cold plugged device exit.

The root cause is that the sPAPR PCI code assumes that a PCI bridge
has a "chassir_nr" property, ie. it is a standard PCI bridge. Other
PCI bridge types don't have that. Not sure yet why this information
is required, I'll check LoPAPR.

In the meantime, since we're in soft freeze, I guess we should
revert Markus's patch and add a big fat comment to explain
what's going on and maybe change the error message to something
more informative, eg. "PCIE-to-PCI bridges are not supported".

Thoughts ?

>  Thomas
>