[jira] [Commented] (HDFS-15963) Unreleased volume references cause an infinite loop

["Kihwal Lee (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-15963?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17364000#comment-17364000 ] 

Kihwal Lee commented on HDFS-15963:
-----------------------------------

We hit this in 2.10 recently. I've cherry-picked it to branch-2.10 with minor conflicts. All new test cases pass.

> Unreleased volume references cause an infinite loop
> ---------------------------------------------------
>
>                 Key: HDFS-15963
>                 URL: https://issues.apache.org/jira/browse/HDFS-15963
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: datanode
>            Reporter: Shuyan Zhang
>            Assignee: Shuyan Zhang
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 3.3.1, 3.4.0
>
>         Attachments: HDFS-15963.001.patch, HDFS-15963.002.patch, HDFS-15963.003.patch
>
>          Time Spent: 4.5h
>  Remaining Estimate: 0h
>
> When BlockSender throws an exception because the meta-data cannot be found, the volume reference obtained by the thread is not released, which causes the thread trying to remove the volume to wait and fall into an infinite loop.
> {code:java}
> boolean checkVolumesRemoved() {
>   Iterator<FsVolumeImpl> it = volumesBeingRemoved.iterator();
>   while (it.hasNext()) {
>     FsVolumeImpl volume = it.next();
>     if (!volume.checkClosed()) {
>       return false;
>     }
>     it.remove();
>   }
>   return true;
> }
> boolean checkClosed() {
>   // always be true.
>   if (this.reference.getReferenceCount() > 0) {
>     FsDatasetImpl.LOG.debug("The reference count for {} is {}, wait to be 0.",
>         this, reference.getReferenceCount());
>     return false;
>   }
>   return true;
> }
> {code}
> At the same time, because the thread has been holding checkDirsLock when removing the volume, other threads trying to acquire the same lock will be permanently blocked.
> Similar problems also occur in RamDiskAsyncLazyPersistService and FsDatasetAsyncDiskService.
> This patch releases the three previously unreleased volume references.



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