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From "Daryn Sharp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-13451) Fix Some Potential NPE
Date Tue, 17 Apr 2018 16:26:00 GMT

    [ https://issues.apache.org/jira/browse/HDFS-13451?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16441106#comment-16441106

Daryn Sharp commented on HDFS-13451:

I disagree with removing the possibility of NPEs by simply ignoring invalid states.  It will
only further mask bugs. It will introduce more insanely difficult to root cause bugs that
would have never happened if the code blew up early due to the invalid state that should be impossible.

The UGI auth method _cannot_ be PROXY w/o having a real user.  The UGI is in an illegal
state that cannot be ignored.

When {{BlockInfo#getDatanode(int)}} returns null it's semantically equivalent to ArrayIndexOutOfBoundsException
– which it arguably should be.  Treating this condition as "ok" and skippable only masks
bugs.  The existing callers are being bad.

The offline image change appears to simply ignore what is effectively a corrupted image format.

> Fix Some Potential NPE
> ----------------------
>                 Key: HDFS-13451
>                 URL: https://issues.apache.org/jira/browse/HDFS-13451
>             Project: Hadoop HDFS
>          Issue Type: Bug
>    Affects Versions: 3.0.0-beta1
>            Reporter: lujie
>            Priority: Major
>         Attachments: HDFS-13451_1.patch
> We have developed a static analysis tool [NPEDetector|https://github.com/lujiefsi/NPEDetector] to
find some potential NPE. Our analysis shows that some callees may return null in corner case(e.g.
node crash , IO exception), some of their callers have  _!=null_ check but some do not
have. In this issue we post a patch which can add  !=null  based on existed !=null  check.
For example:
> callee BlockInfo#getDatanode may return null:
> {code:java}
> public DatanodeDescriptor getDatanode(int index) {
>     DatanodeStorageInfo storage = getStorageInfo(index);
>    return storage == null ? null : storage.getDatanodeDescriptor();
> }
> {code}
> it has 4 callers, 3 of them have !=null checker, like in CacheReplicationMonitor#addNewPendingCached:
> {code:java}
> DatanodeDescriptor datanode = blockInfo.getDatanode(i);
> if (datanode == null) {
>    continue;
> }
> {code}
> but in caller NamenodeFsck#blockIdCK have no !null checker, we add checker just like CacheReplicationMonitor#addNewPendingCached
> {code:java}
> DatanodeDescriptor dn = blockInfo.getDatanode(idx);
> if (dn == null) {
>     continue;
> }
> {code}
> But due to we are not very  familiar with HDFS, hope some expert can review it.
> Thanks!!!!

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