Re: [Qemu-devel] [PATCH v2 03/16] hw/arm/bcm2836: Fix crash with device_add bcm2837 on unsupported machines

[Eduardo Habkost <ehabkost@redhat.com>]

On Fri, Jul 13, 2018 at 10:27:31AM +0200, Thomas Huth wrote:
> When trying to "device_add bcm2837" on a machine that is not suitable for
> this device, you can quickly crash QEMU afterwards, e.g. with "info qtree":
> 
> echo "{'execute':'qmp_capabilities'} {'execute':'device_add', " \
>  "'arguments':{'driver':'bcm2837'}} {'execute': 'human-monitor-command', " \
>  "'arguments': {'command-line': 'info qtree'}}" | \
>  aarch64-softmmu/qemu-system-aarch64 -M integratorcp,accel=qtest -S -qmp stdio
> 
> {"QMP": {"version": {"qemu": {"micro": 50, "minor": 12, "major": 2},
>  "package": "build-all"}, "capabilities": []}}
> {"return": {}}
> {"error": {"class": "GenericError", "desc": "Device 'bcm2837' can not be
>  hotplugged on this machine"}}
> Segmentation fault (core dumped)
> 
> The qdev_set_parent_bus() from instance_init adds a link to the child devices
> which is not valid anymore after the bcm2837 instance has been destroyed.
> Unfortunately, the child devices do not get destroyed / unlinked correctly
> because both object_initialize() and object_property_add_child() increase
> the reference count of the child objects by one, but only one reference
> is dropped when the parent gets removed. So let's use the new functions
> object_initialize_child() and sysbus_init_child_obj() instead to create
> the objects, which will take care of creating the child objects with the
> correct reference count of one.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>

Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>

The usage of &error_abort in code that can be triggered from
device-list-properties still makes me nervous, but that's a
separate issue.


> ---
>  hw/arm/bcm2836.c | 18 ++++++------------
>  1 file changed, 6 insertions(+), 12 deletions(-)
> 
> diff --git a/hw/arm/bcm2836.c b/hw/arm/bcm2836.c
> index 6805a7d..af97b2f 100644
> --- a/hw/arm/bcm2836.c
> +++ b/hw/arm/bcm2836.c
> @@ -51,25 +51,19 @@ static void bcm2836_init(Object *obj)
>      int n;
>  
>      for (n = 0; n < BCM283X_NCPUS; n++) {
> -        object_initialize(&s->cpus[n], sizeof(s->cpus[n]),
> -                          info->cpu_type);
> -        object_property_add_child(obj, "cpu[*]", OBJECT(&s->cpus[n]),
> -                                  &error_abort);
> +        object_initialize_child(obj, "cpu[*]", &s->cpus[n], sizeof(s->cpus[n]),
> +                                info->cpu_type, &error_abort);
>      }
>  
> -    object_initialize(&s->control, sizeof(s->control), TYPE_BCM2836_CONTROL);
> -    object_property_add_child(obj, "control", OBJECT(&s->control), NULL);
> -    qdev_set_parent_bus(DEVICE(&s->control), sysbus_get_default());
> +    sysbus_init_child_obj(obj, "control", &s->control, sizeof(s->control),
> +                          TYPE_BCM2836_CONTROL);
>  
> -    object_initialize(&s->peripherals, sizeof(s->peripherals),
> -                      TYPE_BCM2835_PERIPHERALS);
> -    object_property_add_child(obj, "peripherals", OBJECT(&s->peripherals),
> -                              &error_abort);
> +    sysbus_init_child_obj(obj, "peripherals", &s->peripherals,
> +                          sizeof(s->peripherals), TYPE_BCM2835_PERIPHERALS);
>      object_property_add_alias(obj, "board-rev", OBJECT(&s->peripherals),
>                                "board-rev", &error_abort);
>      object_property_add_alias(obj, "vcram-size", OBJECT(&s->peripherals),
>                                "vcram-size", &error_abort);
> -    qdev_set_parent_bus(DEVICE(&s->peripherals), sysbus_get_default());
>  }
>  
>  static void bcm2836_realize(DeviceState *dev, Error **errp)
> -- 
> 1.8.3.1
> 

-- 
Eduardo