Null pointer in DFSInputStream.readBuffer if read is repeated on
singly-replicated corrupted block
--------------------------------------------------------------------------------------------------
Key: HDFS-3067
URL: https://issues.apache.org/jira/browse/HDFS-3067
Project: Hadoop HDFS
Issue Type: Bug
Reporter: Henry Robinson
Assignee: Henry Robinson
With a singly-replicated block that's corrupted, issuing a read against it
twice in succession (e.g. if ChecksumException is caught by the client) gives a
NullPointerException.
Here's the body of a test that reproduces the problem:
{code}
final short REPL_FACTOR = 1;
final long FILE_LENGTH = 512L;
cluster.waitActive();
FileSystem fs = cluster.getFileSystem();
Path path = new Path("/corrupted");
DFSTestUtil.createFile(fs, path, FILE_LENGTH, REPL_FACTOR, 12345L);
DFSTestUtil.waitReplication(fs, path, REPL_FACTOR);
ExtendedBlock block = DFSTestUtil.getFirstBlock(fs, path);
int blockFilesCorrupted = cluster.corruptBlockOnDataNodes(block);
assertEquals("All replicas not corrupted", REPL_FACTOR,
blockFilesCorrupted);
InetSocketAddress nnAddr =
new InetSocketAddress("localhost", cluster.getNameNodePort());
DFSClient client = new DFSClient(nnAddr, conf);
DFSInputStream dis = client.open(path.toString());
byte[] arr = new byte[(int)FILE_LENGTH];
boolean sawException = false;
try {
dis.read(arr, 0, (int)FILE_LENGTH);
} catch (ChecksumException ex) {
sawException = true;
}
assertTrue(sawException);
sawException = false;
try {
dis.read(arr, 0, (int)FILE_LENGTH); // <-- NPE thrown here
} catch (ChecksumException ex) {
sawException = true;
}
{code}
The stack:
{code}
java.lang.NullPointerException
at
org.apache.hadoop.hdfs.DFSInputStream.readBuffer(DFSInputStream.java:492)
at org.apache.hadoop.hdfs.DFSInputStream.read(DFSInputStream.java:545)
[snip test stack]
{code}
and the problem is that currentNode is null. It's left at null after the first
read, which fails, and then is never refreshed because the condition in read
that protects blockSeekTo is only triggered if the current position is outside
the block's range.
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