liumi created HDFS-12487:
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Summary: FsDatasetSpi.isValidBlock() lacks null pointer check
inside and neither do the callers
Key: HDFS-12487
URL: https://issues.apache.org/jira/browse/HDFS-12487
Project: Hadoop HDFS
Issue Type: Bug
Components: balancer & mover, diskbalancer
Affects Versions: 3.0.0-alpha1
Environment: CentOS 6.8 x64
CPU:4 core
Memory:16GB
Hadoop: Release 3.0.0-alpha4
Reporter: liumi
Fix For: 3.0.0-alpha4
BlockIteratorImpl.nextBlock() will look for the blocks in the source volume, if
there are no blocks any more, it will return null up to
DiskBalancer.getBlockToCopy(). However, the DiskBalancer.getBlockToCopy() will
check whether it's a valid block.
When I look into the FsDatasetSpi.isValidBlock(), I find that it doesn't check
the null pointer! In fact, we firstly need to check whether it's null or not,
or exception will occur.
This bug is hard to find, because the DiskBalancer hardly copy all the data of
one volume to others. Even if some times we may copy all the data of one volume
to other volumes, when the bug occurs, the copy process has already done.
However, when we try to copy all the data of two or more volumes to other
volumes in more than one step, the thread will be shut down, which is caused by
the bug above.
The bug can fixed by two ways:
1)Before the call of FsDatasetSpi.isValidBlock(), we check the null pointer
2)Check the null pointer inside the implementation of
FsDatasetSpi.isValidBlock()
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