qdev: Unrealize must not fail

Devices may have component devices and buses.

Device realization may fail.  Realization is recursive: a device's
realize() method realizes its components, and device_set_realized()
realizes its buses (which should in turn realize the devices on that
bus, except bus_set_realized() doesn't implement that, yet).

When realization of a component or bus fails, we need to roll back:
unrealize everything we realized so far.  If any of these unrealizes
failed, the device would be left in an inconsistent state.  Must not
happen.

device_set_realized() lets it happen: it ignores errors in the roll
back code starting at label child_realize_fail.

Since realization is recursive, unrealization must be recursive, too.
But how could a partly failed unrealize be rolled back?  We'd have to
re-realize, which can fail.  This design is fundamentally broken.

device_set_realized() does not roll back at all.  Instead, it keeps
unrealizing, ignoring further errors.

It can screw up even for a device with no buses: if the lone
dc->unrealize() fails, it still unregisters vmstate, and calls
listeners' unrealize() callback.

bus_set_realized() does not roll back either.  Instead, it stops
unrealizing.

Fortunately, no unrealize method can fail, as we'll see below.

To fix the design error, drop parameter @errp from all the unrealize
methods.

Any unrealize method that uses @errp now needs an update.  This leads
us to unrealize() methods that can fail.  Merely passing it to another
unrealize method cannot cause failure, though.  Here are the ones that
do other things with @errp:

* virtio_serial_device_unrealize()

  Fails when qbus_set_hotplug_handler() fails, but still does all the
  other work.  On failure, the device would stay realized with its
  resources completely gone.  Oops.  Can't happen, because
  qbus_set_hotplug_handler() can't actually fail here.  Pass
  &error_abort to qbus_set_hotplug_handler() instead.

* hw/ppc/spapr_drc.c's unrealize()

  Fails when object_property_del() fails, but all the other work is
  already done.  On failure, the device would stay realized with its
  vmstate registration gone.  Oops.  Can't happen, because
  object_property_del() can't actually fail here.  Pass &error_abort
  to object_property_del() instead.

* spapr_phb_unrealize()

  Fails and bails out when remove_drcs() fails, but other work is
  already done.  On failure, the device would stay realized with some
  of its resources gone.  Oops.  remove_drcs() fails only when
  chassis_from_bus()'s object_property_get_uint() fails, and it can't
  here.  Pass &error_abort to remove_drcs() instead.

Therefore, no unrealize method can fail before this patch.

device_set_realized()'s recursive unrealization via bus uses
object_property_set_bool().  Can't drop @errp there, so pass
&error_abort.

We similarly unrealize with object_property_set_bool() elsewhere,
always ignoring errors.  Pass &error_abort instead.

Several unrealize methods no longer handle errors from other unrealize
methods: virtio_9p_device_unrealize(),
virtio_input_device_unrealize(), scsi_qdev_unrealize(), ...
Much of the deleted error handling looks wrong anyway.

One unrealize methods no longer ignore such errors:
usb_ehci_pci_exit().

Several realize methods no longer ignore errors when rolling back:
v9fs_device_realize_common(), pci_qdev_unrealize(),
spapr_phb_realize(), usb_qdev_realize(), vfio_ccw_realize(),
virtio_device_realize().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200505152926.18877-17-armbru@redhat.com>

5 files changed, 9 insertions, 9 deletions

diff --git a/hw/s390x/css-bridge.c b/hw/s390x/css-bridge.c
index 5d5286b..3f6aec6 100644
--- a/hw/s390x/css-bridge.c
+++ b/hw/s390x/css-bridge.c
@@ -54,7 +54,7 @@ static void ccw_device_unplug(HotplugHandler *hotplug_dev,
 
     css_generate_sch_crws(sch->cssid, sch->ssid, sch->schid, 1, 0);
 
-    object_property_set_bool(OBJECT(dev), false, "realized", NULL);
+    object_property_set_bool(OBJECT(dev), false, "realized", &error_abort);
 }
 
 static void virtual_css_bus_reset(BusState *qbus)
diff --git a/hw/s390x/s390-ccw.c b/hw/s390x/s390-ccw.c
index 569020d..c48510f 100644
--- a/hw/s390x/s390-ccw.c
+++ b/hw/s390x/s390-ccw.c
@@ -132,7 +132,7 @@ out_err_propagate:
     error_propagate(errp, err);
 }
 
-static void s390_ccw_unrealize(S390CCWDevice *cdev, Error **errp)
+static void s390_ccw_unrealize(S390CCWDevice *cdev)
 {
     CcwDevice *ccw_dev = CCW_DEVICE(cdev);
     SubchDev *sch = ccw_dev->sch;
diff --git a/hw/s390x/s390-pci-bus.c b/hw/s390x/s390-pci-bus.c
index ed8be12..c4a4259 100644
--- a/hw/s390x/s390-pci-bus.c
+++ b/hw/s390x/s390-pci-bus.c
@@ -1003,7 +1003,7 @@ static void s390_pcihost_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
                                      pbdev->fh, pbdev->fid);
         bus = pci_get_bus(pci_dev);
         devfn = pci_dev->devfn;
-        object_property_set_bool(OBJECT(dev), false, "realized", NULL);
+        object_property_set_bool(OBJECT(dev), false, "realized", &error_abort);
 
         s390_pci_msix_free(pbdev);
         s390_pci_iommu_free(s, bus, devfn);
@@ -1014,7 +1014,7 @@ static void s390_pcihost_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
         pbdev->fid = 0;
         QTAILQ_REMOVE(&s->zpci_devs, pbdev, link);
         g_hash_table_remove(s->zpci_table, &pbdev->idx);
-        object_property_set_bool(OBJECT(dev), false, "realized", NULL);
+        object_property_set_bool(OBJECT(dev), false, "realized", &error_abort);
     }
 }
 
diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index 64f928f..c1f4bb1 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -752,14 +752,14 @@ out_err:
     g_free(sch);
 }
 
-static void virtio_ccw_device_unrealize(VirtioCcwDevice *dev, Error **errp)
+static void virtio_ccw_device_unrealize(VirtioCcwDevice *dev)
 {
     VirtIOCCWDeviceClass *dc = VIRTIO_CCW_DEVICE_GET_CLASS(dev);
     CcwDevice *ccw_dev = CCW_DEVICE(dev);
     SubchDev *sch = ccw_dev->sch;
 
     if (dc->unrealize) {
-        dc->unrealize(dev, errp);
+        dc->unrealize(dev);
     }
 
     if (sch) {
@@ -1155,11 +1155,11 @@ static void virtio_ccw_busdev_realize(DeviceState *dev, Error **errp)
     virtio_ccw_device_realize(_dev, errp);
 }
 
-static void virtio_ccw_busdev_unrealize(DeviceState *dev, Error **errp)
+static void virtio_ccw_busdev_unrealize(DeviceState *dev)
 {
     VirtioCcwDevice *_dev = (VirtioCcwDevice *)dev;
 
-    virtio_ccw_device_unrealize(_dev, errp);
+    virtio_ccw_device_unrealize(_dev);
 }
 
 static void virtio_ccw_busdev_unplug(HotplugHandler *hotplug_dev,
diff --git a/hw/s390x/virtio-ccw.h b/hw/s390x/virtio-ccw.h
index 3453aa1..c0e3355 100644
--- a/hw/s390x/virtio-ccw.h
+++ b/hw/s390x/virtio-ccw.h
@@ -76,7 +76,7 @@ typedef struct VirtioCcwDevice VirtioCcwDevice;
 typedef struct VirtIOCCWDeviceClass {
     CCWDeviceClass parent_class;
     void (*realize)(VirtioCcwDevice *dev, Error **errp);
-    void (*unrealize)(VirtioCcwDevice *dev, Error **errp);
+    void (*unrealize)(VirtioCcwDevice *dev);
     void (*parent_reset)(DeviceState *dev);
 } VirtIOCCWDeviceClass;