Merge pull request #13501 from ahrtr/reset_ci_after_reload_db_3.5

[3.5] Set the backend again after recovering v3 backend from snapshot

server/etcdserver/server.go

@@ -514,6 +514,9 @@ func NewServer(cfg config.ServerConfig) (srv *EtcdServer, err error) {
 			if be, err = recoverSnapshotBackend(cfg, be, *snapshot, beExist, beHooks); err != nil {
 				cfg.Logger.Panic("failed to recover v3 backend from snapshot", zap.Error(err))
 			}
+			// A snapshot db may have already been recovered, and the old db should have
+			// already been closed in this case, so we should set the backend again.
+			ci.SetBackend(be)
 			s1, s2 := be.Size(), be.SizeInUse()
 			cfg.Logger.Info(
 				"recovered v3 backend from snapshot",