[HDFS-11515] -du throws ConcurrentModificationException

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Invalid
• Affects Version/s: 2.8.0, 3.0.0-alpha2
• Component/s: namenode, shell
• Target Version/s: 3.0.0-beta1, 2.8.1
• Hadoop Flags: Reviewed
• Release Note: In case a directory with subdirectories were removed from a directory that has a snapshot containing the removed subdirectory, hdfs dfs -du on any ancestor of the removed directories ran into a ConcurrentModificationException, and failed.
• Assignee: István Fajth
• Reporter: Wei-Chiu Chuang
• Created: 08/Mar/17 23:24
• Updated: 02/Oct/19 17:15
• Resolved: 01/Sep/17 17:29

Description

HDFS-10797 fixed a disk summary (-du) bug, but it introduced a new bug.

The bug can be reproduced running the following commands:

bash-4.1$ hdfs dfs -mkdir /tmp/d0
bash-4.1$ hdfs dfsadmin -allowSnapshot /tmp/d0
Allowing snaphot on /tmp/d0 succeeded
bash-4.1$ hdfs dfs -touchz /tmp/d0/f4
bash-4.1$ hdfs dfs -mkdir /tmp/d0/d1
bash-4.1$ hdfs dfs -createSnapshot /tmp/d0 s1
Created snapshot /tmp/d0/.snapshot/s1
bash-4.1$ hdfs dfs -mkdir /tmp/d0/d1/d2
bash-4.1$ hdfs dfs -mkdir /tmp/d0/d1/d3
bash-4.1$ hdfs dfs -mkdir /tmp/d0/d1/d2/d4
bash-4.1$ hdfs dfs -mkdir /tmp/d0/d1/d3/d5
bash-4.1$ hdfs dfs -createSnapshot /tmp/d0 s2
Created snapshot /tmp/d0/.snapshot/s2
bash-4.1$ hdfs dfs -rmdir /tmp/d0/d1/d2/d4
bash-4.1$ hdfs dfs -rmdir /tmp/d0/d1/d2
bash-4.1$ hdfs dfs -rmdir /tmp/d0/d1/d3/d5
bash-4.1$ hdfs dfs -rmdir /tmp/d0/d1/d3
bash-4.1$ hdfs dfs -du -h /tmp/d0
du: java.util.ConcurrentModificationException
0 0 /tmp/d0/f4

A ConcurrentModificationException forced du to terminate abruptly.

Correspondingly, NameNode log has the following error:

2017-03-08 14:32:17,673 WARN org.apache.hadoop.ipc.Server: IPC Server handler 4 on 8020, call org.apache.hadoop.hdfs.protocol.ClientProtocol.getContentSumma
ry from 10.0.0.198:49957 Call#2 Retry#0
java.util.ConcurrentModificationException
        at java.util.HashMap$HashIterator.nextEntry(HashMap.java:922)
        at java.util.HashMap$KeyIterator.next(HashMap.java:956)
        at org.apache.hadoop.hdfs.server.namenode.ContentSummaryComputationContext.tallyDeletedSnapshottedINodes(ContentSummaryComputationContext.java:209)
        at org.apache.hadoop.hdfs.server.namenode.INode.computeAndConvertContentSummary(INode.java:507)
        at org.apache.hadoop.hdfs.server.namenode.FSDirectory.getContentSummary(FSDirectory.java:2302)
        at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getContentSummary(FSNamesystem.java:4535)
        at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.getContentSummary(NameNodeRpcServer.java:1087)
        at org.apache.hadoop.hdfs.server.namenode.AuthorizationProviderProxyClientProtocol.getContentSummary(AuthorizationProviderProxyClientProtocol.java:5
63)
        at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.getContentSummary(ClientNamenodeProtocolServerSideTranslatorPB.jav
a:873)
        at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
        at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:617)
        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:1073)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2216)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2212)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:415)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1920)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2210)

The bug is due to a improper use of HashSet, not concurrent operations. Basically, a HashSet can not be updated while an iterator is traversing it.

Issue Links

• breaks: HDFS-10797 Disk usage summary of snapshots causes renamed blocks to get counted twice
• is depended upon by: HDFS-11787 After HDFS-11515, -du still throws ConcurrentModificationException
• is related to: HDFS-11661 GetContentSummary uses excessive amounts of memory