rpc: Prevent concurrent savemempool

src/validation.cpp

@@ -4766,6 +4766,9 @@ bool DumpMempool()
     std::map<uint256, CAmount> mapDeltas;
     std::vector<TxMempoolInfo> vinfo;
 
+    static Mutex dump_mutex;
+    LOCK(dump_mutex);
+
     {
         LOCK(mempool.cs);
         for (const auto &i : mempool.mapDeltas) {