[jira] [Created] (HDFS-17590) `NullPointerException` triggered in `createBlockReader` during retry iteration

["Elmer J Fudd (Jira)" <ji...@apache.org>]

Elmer J Fudd created HDFS-17590:
-----------------------------------

             Summary: `NullPointerException` triggered in `createBlockReader` during retry iteration
                 Key: HDFS-17590
                 URL: https://issues.apache.org/jira/browse/HDFS-17590
             Project: Hadoop HDFS
          Issue Type: Bug
    Affects Versions: 3.4.0
            Reporter: Elmer J Fudd


While reading blocks of data using `DFSInputStream` in `createBlockReader`, a `IOException` originating from `getBlockAt()` that triggers a retry iteration results in a `NullPointerException` when passing `dnInfo` to `addToLocalDeadNodes` in the catch block.

 

This is the relevant callstack portion from our logs (from 3.4.0, but this was occurring with "trunk" versions as new as late June which 3.4.1 builds upon):
{noformat}
...
java.lang.NullPointerException at java.base/
java.util.concurrent.ConcurrentHashMap.putVal(ConcurrentHashMap.java:1011) at java.base/java.util.concurrent.ConcurrentHashMap.put(ConcurrentHashMap.java:1006) at org.apache.hadoop.hdfs.DFSInputStream.addToLocalDeadNodes(DFSInputStream.java:184) at org.apache.hadoop.hdfs.DFSStripedInputStream.createBlockReader(DFSStripedInputStream.java:279) at org.apache.hadoop.hdfs.StripeReader.readChunk(StripeReader.java:304) at org.apache.hadoop.hdfs.StripeReader.readStripe(StripeReader.java:335) at org.apache.hadoop.hdfs.DFSStripedInputStream.fetchBlockByteRange(DFSStripedInputStream.java:504) at org.apache.hadoop.hdfs.DFSInputStream.pread(DFSInputStream.java:1472) at org.apache.hadoop.hdfs.DFSInputStream.read(DFSInputStream.java:1436) at org.apache.hadoop.fs.FSInputStream.readFully(FSInputStream.java:124) at org.apache.hadoop.fs.FSDataInputStream.readFully(FSDataInputStream.java:119) ...{noformat}
 

What we observe is that `getBlockAt()` thorws an `IOException` [here|] 

{code:java}
//check offset 
if (offset < 0 || offset >= getFileLength()) { 
  throw new IOException("offset < 0 || offset >= getFileLength(), offset=" 
      + offset 
      + ", locatedBlocks=" + locatedBlocks); 
} 
{code}
 

This is eventually caught in `createBlockReader`. The catch block attempts to handle the error and, as part of the error handling, invokes the *`*addToLocalDeadNodes` method. See that a `dnInfo` object passed to this method is `NULL` as it wasn't fully allocated [here|https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSStripedInputStream.java#L247], which results in a `NullPointerException`. 

 

To sum up, this is the failure path according to the logs:
 # `IOException` is thrown in `getBlockAt` ([code|https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSInputStream.java#L479])
 # The exception propagates to `getBlockGroupAt` ([code|https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSStripedInputStream.java#L476])
 # It further propagates to `refreshLocatedBlock` ([code|https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSStripedInputStream.java#L459]
 # `IOException` caught in `createBlockReader` ([code|https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSStripedInputStream.java#L247])
 # Error handling in the catch block of `createBlockReader` invokes `addToLocalDeadNodes` ([code|https://github.com/apache/hadoop/blob/4525c7e35ea22d7a6350b8af10eb8d2ff68376e7/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/DFSStripedInputStream.java#L281])

 # Execution throws `NullPointerException` since `dnInfo` is NULL

 

A simple fix as a `NULL` check to add only non-NULL `dnInfo` objects to the hash map, and similarly adjusting the log messages in the `catch` block, should solve the issue.



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