[Qemu-devel] [PATCH] call HotplugHandler->plug() as the last step in device realization

[Igor Mammedov]

When [2] was fixed it was agreed that adding and calling post_plug()
callback after device_reset() was low risk approach to hotfix issue
right before release. So it was merged instead of moving already
existing plug() callback after device_reset() is called which would
be more risky and require all plug() callbacks audit.

Looking at the current plug() callbacks, it doesn't seem that moving
plug() callback after device_reset() is breaking anything, so here
goes agreed upon [3] proper fix which essentially reverts [1][2]
and moves plug() callback after device_reset().
This way devices always comes to plug() stage, after it's been fully
initialized (including being reset), which fixes race condition [2]
without need for an extra post_plug() callback.

 1. (25e897881 "qdev: add HotplugHandler->post_plug() callback")
 2. (8449bcf94 "virtio-scsi: fix hotplug ->reset() vs event race")
 3. https://www.mail-archive.com/address@hidden/msg549915.html

Signed-off-by: Igor Mammedov <address@hidden>
---
TODO:
 remove usage of Error** from plug() callback, we need to factor out
 pre_plug part from plug() callbacks, before proceeding with it.
 DavidH has recently finished it for pc-dimm/memory_devices, cpus
 mostly have pre_plug parts factored out, but there still are parts
 that could fail so it needs some more work to eliminate failure points
 from plug() callbacks. Meanwhile, I'll plan to treat other misc
 handlers (pci[e]/acpi/usb/...) and introduce pre_plug() where
 necessary.
---
 include/hw/hotplug.h  | 11 -----------
 hw/core/hotplug.c     | 10 ----------
 hw/core/qdev.c        | 16 ++++++----------
 hw/scsi/virtio-scsi.c | 11 +----------
 4 files changed, 7 insertions(+), 41 deletions(-)

diff --git a/include/hw/hotplug.h b/include/hw/hotplug.h
index 51541d6..1a0516a 100644
--- a/include/hw/hotplug.h
+++ b/include/hw/hotplug.h
@@ -47,8 +47,6 @@ typedef void (*hotplug_fn)(HotplugHandler *plug_handler,
  * @parent: Opaque parent interface.
  * @pre_plug: pre plug callback called at start of device.realize(true)
  * @plug: plug callback called at end of device.realize(true).
- * @post_plug: post plug callback called after device.realize(true) and device
- *             reset
  * @unplug_request: unplug request callback.
  *                  Used as a means to initiate device unplug for devices that
  *                  require asynchronous unplug handling.
@@ -63,7 +61,6 @@ typedef struct HotplugHandlerClass {
     /* <public> */
     hotplug_fn pre_plug;
     hotplug_fn plug;
-    void (*post_plug)(HotplugHandler *plug_handler, DeviceState *plugged_dev);
     hotplug_fn unplug_request;
     hotplug_fn unplug;
 } HotplugHandlerClass;
@@ -87,14 +84,6 @@ void hotplug_handler_pre_plug(HotplugHandler *plug_handler,
                               Error **errp);
 
 /**
- * hotplug_handler_post_plug:
- *
- * Call #HotplugHandlerClass.post_plug callback of @plug_handler.
- */
-void hotplug_handler_post_plug(HotplugHandler *plug_handler,
-                               DeviceState *plugged_dev);
-
-/**
  * hotplug_handler_unplug_request:
  *
  * Calls #HotplugHandlerClass.unplug_request callback of @plug_handler.
diff --git a/hw/core/hotplug.c b/hw/core/hotplug.c
index 2253072..17ac986 100644
--- a/hw/core/hotplug.c
+++ b/hw/core/hotplug.c
@@ -35,16 +35,6 @@ void hotplug_handler_plug(HotplugHandler *plug_handler,
     }
 }
 
-void hotplug_handler_post_plug(HotplugHandler *plug_handler,
-                               DeviceState *plugged_dev)
-{
-    HotplugHandlerClass *hdc = HOTPLUG_HANDLER_GET_CLASS(plug_handler);
-
-    if (hdc->post_plug) {
-        hdc->post_plug(plug_handler, plugged_dev);
-    }
-}
-
 void hotplug_handler_unplug_request(HotplugHandler *plug_handler,
                                     DeviceState *plugged_dev,
                                     Error **errp)
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 046d8f1..6b3cc55 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -832,14 +832,6 @@ static void device_set_realized(Object *obj, bool value, 
Error **errp)
 
         DEVICE_LISTENER_CALL(realize, Forward, dev);
 
-        if (hotplug_ctrl) {
-            hotplug_handler_plug(hotplug_ctrl, dev, &local_err);
-        }
-
-        if (local_err != NULL) {
-            goto post_realize_fail;
-        }
-
         /*
          * always free/re-initialize here since the value cannot be cleaned up
          * in device_unrealize due to its usage later on in the unplug path
@@ -869,8 +861,12 @@ static void device_set_realized(Object *obj, bool value, 
Error **errp)
         dev->pending_deleted_event = false;
 
         if (hotplug_ctrl) {
-            hotplug_handler_post_plug(hotplug_ctrl, dev);
-        }
+            hotplug_handler_plug(hotplug_ctrl, dev, &local_err);
+            if (local_err != NULL) {
+                goto child_realize_fail;
+            }
+       }
+
     } else if (!value && dev->realized) {
         Error **local_errp = NULL;
         QLIST_FOREACH(bus, &dev->child_bus, sibling) {
diff --git a/hw/scsi/virtio-scsi.c b/hw/scsi/virtio-scsi.c
index 5a3057d..3aa9971 100644
--- a/hw/scsi/virtio-scsi.c
+++ b/hw/scsi/virtio-scsi.c
@@ -797,16 +797,8 @@ static void virtio_scsi_hotplug(HotplugHandler 
*hotplug_dev, DeviceState *dev,
         virtio_scsi_acquire(s);
         blk_set_aio_context(sd->conf.blk, s->ctx);
         virtio_scsi_release(s);
-    }
-}
 
-/* Announce the new device after it has been plugged */
-static void virtio_scsi_post_hotplug(HotplugHandler *hotplug_dev,
-                                     DeviceState *dev)
-{
-    VirtIODevice *vdev = VIRTIO_DEVICE(hotplug_dev);
-    VirtIOSCSI *s = VIRTIO_SCSI(vdev);
-    SCSIDevice *sd = SCSI_DEVICE(dev);
+    }
 
     if (virtio_vdev_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG)) {
         virtio_scsi_acquire(s);
@@ -976,7 +968,6 @@ static void virtio_scsi_class_init(ObjectClass *klass, void 
*data)
     vdc->start_ioeventfd = virtio_scsi_dataplane_start;
     vdc->stop_ioeventfd = virtio_scsi_dataplane_stop;
     hc->plug = virtio_scsi_hotplug;
-    hc->post_plug = virtio_scsi_post_hotplug;
     hc->unplug = virtio_scsi_hotunplug;
 }
 
-- 
2.7.4