hw/qdev: Check machine_hotplug_handler in hotplug_unplug_allowed_common

Commit 03fcbd9dc508 ("qdev: Check for the availability of a hotplug
controller before adding a device") says:

 > The qdev_unplug() function contains a g_assert(hotplug_ctrl)
 > statement, so QEMU crashes when the user tries to device_add +
 > device_del a device that does not have a corresponding hotplug
 > controller.

 > The code in qdev_device_add() already checks whether the bus has a
 > proper hotplug controller, but for devices that do not have a
 > corresponding bus, here is no appropriate check available yet. In that
 > case we should check whether the machine itself provides a suitable
 > hotplug controller and refuse to plug the device if none is available.

However, it forgot to add the corresponding check to qdev_unplug().

Check the machine hotplug handler once in the common
qdev_hotplug_unplug_allowed_common() helper so both hotplug
and hot-unplug path are covered.

Fixes: 7716b8ca74 ("qdev: HotplugHandler: Add support for unplugging BUS-less devices")
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
[PMD: Split from bigger patch, part 6/6]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <20250110091908.64454-7-philmd@linaro.org>

hw/core/qdev-hotplug.c

@@ -48,6 +48,16 @@ static bool qdev_hotplug_unplug_allowed_common(DeviceState *dev, BusState *bus,
                        bus->name);
             return false;
         }
+    } else {
+        if (!qdev_get_machine_hotplug_handler(dev)) {
+            /*
+             * No bus, no machine hotplug handler --> device is not hotpluggable
+             */
+            error_setg(errp,
+                       "Device '%s' can not be hotplugged on this machine",
+                       object_get_typename(OBJECT(dev)));
+            return false;
+        }
     }
 
     return true;

system/qdev-monitor.c

@@ -684,17 +684,9 @@ DeviceState *qdev_device_add_from_qdict(const QDict *opts,
     dev = qdev_new(driver);
 
     /* Check whether the hotplug is allowed by the machine */
-    if (phase_check(PHASE_MACHINE_READY)) {
-        if (!qdev_hotplug_allowed(dev, bus, errp)) {
-            goto err_del_dev;
-        }
-
-        if (!bus && !qdev_get_machine_hotplug_handler(dev)) {
-            /* No bus, no machine hotplug handler --> device is not hotpluggable */
-            error_setg(errp, "Device '%s' can not be hotplugged on this machine",
-                       driver);
-            goto err_del_dev;
-        }
+    if (phase_check(PHASE_MACHINE_READY) &&
+        !qdev_hotplug_allowed(dev, bus, errp)) {
+        goto err_del_dev;
     }
 
     /*