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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