For a sufficiently large value of blocks, the DN Scanner may request a random
number with a negative seed value.
----------------------------------------------------------------------------------------------------------------
Key: HDFS-2541
URL: https://issues.apache.org/jira/browse/HDFS-2541
Project: Hadoop HDFS
Issue Type: Bug
Components: data-node
Affects Versions: 0.20.1
Reporter: Harsh J
Assignee: Harsh J
Fix For: 0.24.0
Running off 0.20-security, I noticed that one could get the following exception
when scanners are used:
{code}
DataXceiver
java.lang.IllegalArgumentException: n must be positive
at java.util.Random.nextInt(Random.java:250)
at
org.apache.hadoop.hdfs.server.datanode.DataBlockScanner.getNewBlockScanTime(DataBlockScanner.java:251)
at
org.apache.hadoop.hdfs.server.datanode.DataBlockScanner.addBlock(DataBlockScanner.java:268)
at
org.apache.hadoop.hdfs.server.datanode.DataXceiver.writeBlock(DataXceiver.java:432)
at org.apache.hadoop.hdfs.server.datanode.DataXceiver.run(DataXceiver.java:122)
{code}
This is cause the period, determined in the DataBlockScanner (0.20+) or
BlockPoolSliceScanner (0.23+), is cast to an integer before its sent to a
Random.nextInt(...) call. For sufficiently large values of the long 'period',
the casted integer may be negative. This is not accounted for. I'll attach a
sample test that shows this possibility with the numbers.
We should ensure we do a Math.abs(...) before we send it to the
Random.nextInt(...) call to avoid this.
With this bug, the maximum # of blocks a scanner may hold in its blocksMap
without opening up the chance for beginning this exception (intermittent, as
blocks continue to grow) would be 3582718.
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