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https://issues.apache.org/jira/browse/HDFS-9781?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15193797#comment-15193797
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Virajith Jalaparti commented on HDFS-9781:
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Hi [~xiaochen] and [~jojochuang],
I encountered this test case failing and when I tried to understand the reason,
I realized this might be a general problem (not particular to this test) due to
the way {{FsDatasetImpl#getBlockReports()}} and
{{FsDatasetImpl#removeVolumes()}} inconsistently handle {{volumeMap}} and
{{volumes}} under the {{FsDatasetImpl}} instance lock.
{{FsDatasetImpl#removeVolumes()}} refers to both the objects under the lock.
{{FsDatasetImpl#getBlockReports()}} calls {{volumes.getVolumes()}} without the
lock but refers to {{volumeMap}} with the lock. I think this is what is causing
the NPE problem due to the following sequence of events:
# {{volumes.removeVolume()}} is called in {{FsDatasetImpl#removeVolumes()}}.
Suppose this removes Volume A.
# {{volumes.getVolumes()}} is called in {{FsDatasetImpl#getBlockReports()}}.
This would return all volumes except Volume A.
# {{volumes.waitVolumeRemoved()}} (added as part of HDFS-9701) is called in
{{FsDatasetImpl#removeVolumes()}} which releases the lock.
# The for loop {{volumeMap.replicas(bpid)}} in
{{FsDatasetImpl#getBlockReports()}} starts running. This would return
{{ReplicaInfo}} s that are stored on Volume A as
{{FsDatasetImpl#removeVolumes()}} did not still delete them.
If I understand correctly, {{volumes.waitVolumeRemoved()}} was added in
HDFS-9701 to avoid the deadlock issue being addressed.
One way to fix this might be to call {{volumes.waitVolumeRemoved()}} before
{{volumes.removeVolume()}} in {{FsDatasetImpl#removeVolumes()}} and make
{{FsDatasetImpl#getBlockReports()}} hold the lock while it is referring to both
{{volumes}} and {{volumeMap}} i.e., move {{synchronized(this)}} before
{{volumes.getVolumes()}}.
> FsDatasetImpl#getBlockReports can occasionally throw NullPointerException
> -------------------------------------------------------------------------
>
> Key: HDFS-9781
> URL: https://issues.apache.org/jira/browse/HDFS-9781
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode
> Affects Versions: 3.0.0
> Environment: Jenkins
> Reporter: Wei-Chiu Chuang
> Assignee: Xiao Chen
> Attachments: HDFS-9781.01.patch
>
>
> FsDatasetImpl#getBlockReports occasionally throws NPE. The NPE caused
> TestFsDatasetImpl#testRemoveVolumeBeingWritten to time out, because the test
> waits for the call to FsDatasetImpl#getBlockReports to complete without
> exceptions.
> Additionally, the test should be updated to identify an expected exception,
> using {{GenericTestUtils.assertExceptionContains()}}
> {noformat}
> Exception in thread "Thread-20" java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.getBlockReports(FsDatasetImpl.java:1709)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.TestFsDatasetImpl$1BlockReportThread.run(TestFsDatasetImpl.java:587)
> 2016-02-08 15:47:30,379 [Thread-21] WARN impl.TestFsDatasetImpl
> (TestFsDatasetImpl.java:run(606)) - Exception caught. This should not affect
> the test
> java.io.IOException: Failed to move meta file for ReplicaBeingWritten,
> blk_0_0, RBW
> getNumBytes() = 0
> getBytesOnDisk() = 0
> getVisibleLength()= 0
> getVolume() =
> /home/weichiu/hadoop/hadoop-hdfs-project/hadoop-hdfs/target/test/data/Nmi6rYndvr/data0/current
> getBlockFile() =
> /home/weichiu/hadoop/hadoop-hdfs-project/hadoop-hdfs/target/test/data/Nmi6rYndvr/data0/current/bpid-0/current/rbw/blk_0
> bytesAcked=0
> bytesOnDisk=0 from
> /home/weichiu/hadoop/hadoop-hdfs-project/hadoop-hdfs/target/test/data/Nmi6rYndvr/data0/current/bpid-0/current/rbw/blk_0_0.meta
> to
> /home/weichiu/hadoop/hadoop-hdfs-project/hadoop-hdfs/target/test/data/Nmi6rYndvr/data0/current/bpid-0/current/finalized/subdir0/subdir0/blk_0_0.meta
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.moveBlockFiles(FsDatasetImpl.java:857)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.BlockPoolSlice.addFinalizedBlock(BlockPoolSlice.java:295)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsVolumeImpl.addFinalizedBlock(FsVolumeImpl.java:819)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.finalizeReplica(FsDatasetImpl.java:1620)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.finalizeBlock(FsDatasetImpl.java:1601)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.TestFsDatasetImpl$1ResponderThread.run(TestFsDatasetImpl.java:603)
> Caused by: java.io.IOException:
> renameTo(src=/home/weichiu/hadoop/hadoop-hdfs-project/hadoop-hdfs/target/test/data/Nmi6rYndvr/data0/current/bpid-0/current/rbw/blk_0_0.meta,
>
> dst=/home/weichiu/hadoop/hadoop-hdfs-project/hadoop-hdfs/target/test/data/Nmi6rYndvr/data0/current/bpid-0/current/finalized/subdir0/subdir0/blk_0_0.meta)
> failed.
> at org.apache.hadoop.io.nativeio.NativeIO.renameTo(NativeIO.java:873)
> at
> org.apache.hadoop.hdfs.server.datanode.fsdataset.impl.FsDatasetImpl.moveBlockFiles(FsDatasetImpl.java:855)
> ... 5 more
> 2016-02-08 15:47:34,381 [Thread-19] INFO impl.FsDatasetImpl
> (FsVolumeList.java:waitVolumeRemoved(287)) - Volume reference is released.
> 2016-02-08 15:47:34,384 [Thread-19] INFO impl.TestFsDatasetImpl
> (TestFsDatasetImpl.java:testRemoveVolumeBeingWritten(622)) - Volumes removed
> {noformat}
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