Fix concurrency bug in IMC that could lead to negative total indexing bytes

core/src/main/java/org/elasticsearch/indices/IndexingMemoryController.java

@@ -251,21 +251,29 @@ public class IndexingMemoryController extends AbstractComponent implements Index
         /** Shard calls this on each indexing/delete op */
         public void bytesWritten(int bytes) {
             long totalBytes = bytesWrittenSinceCheck.addAndGet(bytes);
+            assert totalBytes >= 0      ;
             while (totalBytes > indexingBuffer.bytes()/30) {
+
                 if (runLock.tryLock()) {
                     try {
+                        // Must pull this again because it may have changed since we first checked:
+                        totalBytes = bytesWrittenSinceCheck.get();
+                        if (totalBytes > indexingBuffer.bytes()/30) {
                             bytesWrittenSinceCheck.addAndGet(-totalBytes);
                             // NOTE: this is only an approximate check, because bytes written is to the translog, vs indexing memory buffer which is
                             // typically smaller but can be larger in extreme cases (many unique terms).  This logic is here only as a safety against
                             // thread starvation or too infrequent checking, to ensure we are still checking periodically, in proportion to bytes
                             // processed by indexing:
                             runUnlocked();
+                        }
                     } finally {
                         runLock.unlock();
                     }
-                    // Could be while we were checking, more bytes arrived:
+
-                    totalBytes = bytesWrittenSinceCheck.addAndGet(bytes);
+                    // Must get it again since other threads could have increased it while we were in runUnlocked
+                    totalBytes = bytesWrittenSinceCheck.get();
                 } else {
+                    // Another thread beat us to it: let them do all the work, yay!
                     break;
                 }
             }