migration/block: Apply late-block-active behavior to postcopy

Postcopy never cared about late-block-active.  However there's no mention
in the capability that it doesn't apply to postcopy.

Considering that we _assumed_ late activation is always good, do that too
for postcopy unconditionally, just like precopy.  After this patch, we
should have unified the behavior across all.

Signed-off-by: Peter Xu <[email protected]>
Reviewed-by: Fabiano Rosas <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Fabiano Rosas <[email protected]>

Author: xzpeter

migration/savevm.c

@@ -2137,22 +2137,21 @@ static void loadvm_postcopy_handle_run_bh(void *opaque)
 
     trace_vmstate_downtime_checkpoint("dst-postcopy-bh-announced");
 
-    /* Make sure all file formats throw away their mutable metadata.
-     * If we get an error here, just don't restart the VM yet. */
-    bdrv_activate_all(&local_err);
-    if (local_err) {
-        error_report_err(local_err);
-        local_err = NULL;
-        autostart = false;
-    }
-
-    trace_vmstate_downtime_checkpoint("dst-postcopy-bh-cache-invalidated");
-
     dirty_bitmap_mig_before_vm_start();
 
     if (autostart) {
-        /* Hold onto your hats, starting the CPU */
-        vm_start();
+        /*
+         * Make sure all file formats throw away their mutable metadata.
+         * If we get an error here, just don't restart the VM yet.
+         */
+        bdrv_activate_all(&local_err);
+        trace_vmstate_downtime_checkpoint("dst-postcopy-bh-cache-invalidated");
+        if (local_err) {
+            error_report_err(local_err);
+            local_err = NULL;
+        } else {
+            vm_start();
+        }
     } else {
         /* leave it paused and let management decide when to start the CPU */
         runstate_set(RUN_STATE_PAUSED);