Uploaded image for project: 'Hadoop HDFS'
  1. Hadoop HDFS
  2. HDFS-15644

Failed volumes can cause DNs to stop block reporting

    XMLWordPrintableJSON

    Details

      Description

      Daryn Sharp found a corner case where remove failed volumes can cause a NPE in FsDataSetImpl.getBlockReports().

      Scenario:

      • Inside Datanode#HandleVolumeFailures(), removing a failed volume is a 2-step process.
        • First it's removed from from the volumes list
        • Later in time are the replicas scrubbed from the volume map
      • A concurrent thread generating blockReports may access the replicaMap accessing a non existing VolumeID.

      He made a fix for that and we have been using it on our clusters since Hadoop-2.7.

      By analyzing the code, the bug is still applicable to Trunk.

      • The path Datanode#removeVolumes() is safe because the two step process in FsDataImpl.removeVolumes() FsDatasetImpl.java#L577 is protected by datasetWriteLock .
      • The path Datanode#handleVolumeFailures() is not safe because the failed volume is removed from the list without acquiring datasetWriteLock.FsVolumList#239

      The race condition can cause the caller of getBlockReports() to throw NPE if the RUR is referring to a volume that has already been removed FsDatasetImpl.java#L1976.

              case RUR:
                ReplicaInfo orig = b.getOriginalReplica();
                builders.get(volStorageID).add(orig);
                break;
      

        Attachments

        1. HDFS-15644-branch-2.10.002.patch
          2 kB
          Ahmed Hussein
        2. HDFS-15644.002.patch
          2 kB
          Ahmed Hussein
        3. HDFS-15644.001.patch
          2 kB
          Ahmed Hussein

          Activity

            People

            • Assignee:
              ahussein Ahmed Hussein
              Reporter:
              ahussein Ahmed Hussein
            • Votes:
              0 Vote for this issue
              Watchers:
              6 Start watching this issue

              Dates

              • Created:
                Updated:
                Resolved: