Re: [PATCH v2] qdev: Report an error for machine without HotplugHandler

[Markus Armbruster <armbru@redhat.com>]

Akihiko Odaki <akihiko.odaki@daynix.com> writes:

> The HotplugHandler of the machine will be used when the parent bus does
> not exist, but the machine may not have one. Report an error in such a
> case instead of aborting.
>
> Fixes: 7716b8ca74 ("qdev: HotplugHandler: Add support for unplugging BUS-less devices")
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>

Do you have a reproducer for the crash?

> ---
> Changes in v2:
> - Fixed indention.
> - Link to v1: https://lore.kernel.org/r/20231202-bus-v1-1-f7540e3a8d62@daynix.com
> ---
>  system/qdev-monitor.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/system/qdev-monitor.c b/system/qdev-monitor.c
> index a13db763e5..5fe5d49c20 100644
> --- a/system/qdev-monitor.c
> +++ b/system/qdev-monitor.c
> @@ -927,9 +927,16 @@ void qdev_unplug(DeviceState *dev, Error **errp)
   void qdev_unplug(DeviceState *dev, Error **errp)
   {
       DeviceClass *dc = DEVICE_GET_CLASS(dev);
       HotplugHandler *hotplug_ctrl;
       HotplugHandlerClass *hdc;
       Error *local_err = NULL;

       if (qdev_unplug_blocked(dev, errp)) {
           return;
       }

       if (dev->parent_bus && !qbus_is_hotpluggable(dev->parent_bus)) {
           error_setg(errp, QERR_BUS_NO_HOTPLUG, dev->parent_bus->name);
           return;
       }

       if (!dc->hotpluggable) {
           error_setg(errp, QERR_DEVICE_NO_HOTPLUG,
                      object_get_typename(OBJECT(dev)));
           return;
       }

       if (!migration_is_idle() && !dev->allow_unplug_during_migration) {
           error_setg(errp, "device_del not allowed while migrating");
           return;
       }

>      qdev_hot_removed = true;
>  
>      hotplug_ctrl = qdev_get_hotplug_handler(dev);
> -    /* hotpluggable device MUST have HotplugHandler, if it doesn't
> -     * then something is very wrong with it */
> -    g_assert(hotplug_ctrl);
> +    if (!hotplug_ctrl) {
> +        /*
> +         * hotpluggable bus MUST have HotplugHandler, if it doesn't
> +         * then something is very wrong with it
> +         */
> +        assert(!dev->parent_bus);
> +
> +        error_setg(errp, "The machine does not support hotplugging for a device without parent bus");
> +        return;
> +    }

Extended version of my question above: what are the devices where
qdev_get_hotplug_handler(dev) returns null here?

>  
>      /* If device supports async unplug just request it to be done,
>       * otherwise just remove it synchronously */
>
> ---
> base-commit: 4705fc0c8511d073bee4751c3c974aab2b10a970
> change-id: 20231202-bus-75a454c5d959
>
> Best regards,