[HDFS-7066] LazyWriter#evictBlocks misses a null check for replicaState

• Type: Sub-task
• Status: Closed
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: HDFS-6581
• Fix Version/s: 2.6.0
• Component/s: datanode
• Hadoop Flags: Reviewed
• Assignee: Xiaoyu Yao
• Reporter: Xiaoyu Yao
• Created: 15/Sep/14 22:02
• Updated: 01/Dec/14 03:09
• Resolved: 15/Sep/14 22:29

Description

LazyWriter#evictBlocks (added for HDFS-6581) misses a null check for replicaState. As a result, there are many NPEs in the debug log under certain conditions.

2014-09-15 14:27:10,820 DEBUG impl.FsDatasetImpl (FsDatasetImpl.java:evictBlocks(2335)) - Evicting block null
2014-09-15 14:27:10,821 WARN  impl.FsDatasetImpl (FsDatasetImpl.java:run(2409)) - Ignoring exception in LazyWriter:
java.lang.NullPointerException
	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl$LazyWriter.evictBlocks(FsDatasetImpl.java:2343)
	at org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl$LazyWriter.run(FsDatasetImpl.java:2396)
	at java.lang.Thread.run(Thread.java:745)

The proposed fix is to break if there is no candidate available to evict.

	while (iterations++ < MAX_BLOCK_EVICTIONS_PER_ITERATION &&
            transientFreeSpaceBelowThreshold()) {
           LazyWriteReplicaTracker.ReplicaState replicaState =
               lazyWriteReplicaTracker.getNextCandidateForEviction();

           ++++++++++++++++++++
	    if (replicaState == null) {
              break;
           }
           ++++++++++++++++++++

           if (LOG.isDebugEnabled()) {
             LOG.debug("Evicting block " + replicaState);
           }