emopers created HDFS-9649:
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Summary: NNStorage does not synchronize iteration on a
synchronized list
Key: HDFS-9649
URL: https://issues.apache.org/jira/browse/HDFS-9649
Project: Hadoop HDFS
Issue Type: Bug
Reporter: emopers
In line 839 of NNStroage.java#reportErrorsOnDirectories, the synchronized list,
`sds` is iterated in an unsynchronized manner, but according to [Oracle Java 7
API
specification](http://docs.oracle.com/javase/7/docs/api/java/util/Collections.html#synchronizedList(java.util.List)),
this is not thread-safe and can lead to non-deterministic behavior.
This could be fix by synchronizing the iteration on `sds`. The synchronized
list is passed to method `reportErrorsOnDirectories` from
(https://github.com/facebookarchive/hadoop-20/blob/2a29bc6ecf30edb1ad8dbde32aa49a317b4d44f4/src/hdfs/org/apache/hadoop/hdfs/server/namenode/FSImage.java#L508)
I have already submitted submitted a PR at
https://github.com/apache/hadoop/pull/64 . Let me know if it looks good so that
I can generate patch and submit it.
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