migration/colo.c: Move colo_notify_compares_event to the right place

If the secondary has to failover during checkpointing, it still is
in the old state (i.e. different state than primary). Thus we can't
expose the primary state until after the checkpoint is sent.

This fixes sporadic connection reset of client connections during
failover.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Message-Id: <d4555dd5146a54518c4d9d4efd996b7c745c6687.1589193382.git.lukasstraub2@web.de>
Reviewed-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/colo.c

@@ -436,12 +436,6 @@ static int colo_do_checkpoint_transaction(MigrationState *s,
         goto out;
     }
 
-    qemu_event_reset(&s->colo_checkpoint_event);
-    colo_notify_compares_event(NULL, COLO_EVENT_CHECKPOINT, &local_err);
-    if (local_err) {
-        goto out;
-    }
-
     /* Disable block migration */
     migrate_set_block_enabled(false, &local_err);
     if (local_err) {
@@ -503,6 +497,12 @@ static int colo_do_checkpoint_transaction(MigrationState *s,
         goto out;
     }
 
+    qemu_event_reset(&s->colo_checkpoint_event);
+    colo_notify_compares_event(NULL, COLO_EVENT_CHECKPOINT, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
     colo_receive_check_message(s->rp_state.from_dst_file,
                        COLO_MESSAGE_VMSTATE_LOADED, &local_err);
     if (local_err) {