HBASE-26944 Possible resource leak while creating new region scanner (#…

…4339)

* HBASE-26944 Possible resource leak while creating new region scanner

Signed-off-by: Duo Zhang <zhangduo@apache.org>

hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/RSRpcServices.java

@@ -3203,8 +3203,16 @@ private Pair<String, RegionScannerHolder> newRegionScanner(ScanRequest request,
     RegionScannerImpl coreScanner = region.getScanner(scan);
     Shipper shipper = coreScanner;
     RegionScanner scanner = coreScanner;
-    if (region.getCoprocessorHost() != null) {
-      scanner = region.getCoprocessorHost().postScannerOpen(scan, scanner);
+    try {
+      if (region.getCoprocessorHost() != null) {
+        scanner = region.getCoprocessorHost().postScannerOpen(scan, scanner);
+      }
+    } catch (Exception e) {
+      // Although region coprocessor is for advanced users and they should take care of the
+      // implementation to not damage the HBase system, closing the scanner on exception here does
+      // not have any bad side effect, so let's do it
+      scanner.close();
+      throw e;
     }
     long scannerId = scannerIdGenerator.generateNewScannerId();
     builder.setScannerId(scannerId);