The Error ** argument must be NULL, &error_abort, &error_fatal, or a
pointer to a variable containing NULL.  Passing an argument of the
latter kind twice without clearing it in between is wrong: if the
first call sets an error, it no longer points to NULL for the second
call.

qmp_xen_colo_do_checkpoint() passes @errp first to
replication_do_checkpoint_all(), and then to
colo_notify_filters_event().  If both fail, this will trip the
assertion in error_setv().

Similar code in secondary_vm_do_failover() calls
colo_notify_filters_event() only after replication_do_checkpoint_all()
succeeded.  Do the same here.

Fixes: 0e8818f023616677416840d6ddc880db8de3c967
Cc: Zhang Chen <chen.zhang@intel.com>
Cc: zhanghailiang <zhang.zhanghailiang@huawei.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Zhang Chen <chen.zhang@intel.com>
Message-Id: <20200422130719.28225-12-armbru@redhat.com>
---
 migration/colo.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/migration/colo.c b/migration/colo.c
index a54ac84f41..1b3493729b 100644
--- a/migration/colo.c
+++ b/migration/colo.c
@@ -263,7 +263,13 @@ ReplicationStatus *qmp_query_xen_replication_status(Error **errp)
 
 void qmp_xen_colo_do_checkpoint(Error **errp)
 {
-    replication_do_checkpoint_all(errp);
+    Error *err = NULL;
+
+    replication_do_checkpoint_all(&err);
+    if (err) {
+        error_propagate(errp, err);
+        return;
+    }
     /* Notify all filters of all NIC to do checkpoint */
     colo_notify_filters_event(COLO_EVENT_CHECKPOINT, errp);
 }
-- 
2.21.1