Ding Yuan created HBASE-10452:
---------------------------------
Summary: Potential bugs in exception handlers
Key: HBASE-10452
URL: https://issues.apache.org/jira/browse/HBASE-10452
Project: HBase
Issue Type: Bug
Components: Client, master, regionserver, util
Affects Versions: 0.96.1
Reporter: Ding Yuan
Hi HBase developers,
We are a group of researchers on software reliability. Recently we did a study
and found that majority of the most severe failures in HBase are caused by bugs
in exception handling logic -- that it is hard to anticipate all the possible
real-world error scenarios. Therefore we built a simple checking tool that
automatically detects some bug patterns that have caused some very severe
real-world failures. I am reporting some of the results here. Any feedback is
much appreciated!
=========================
Case 1:
Line: 134, File:
"org/apache/hadoop/hbase/regionserver/RegionMergeRequest.java"
{noformat}
protected void releaseTableLock() {
if (this.tableLock != null) {
try {
this.tableLock.release();
} catch (IOException ex) {
LOG.warn("Could not release the table lock", ex);
//TODO: if we get here, and not abort RS, this lock will never be
released
}
}
{noformat}
The lock is not released if the exception occurs, causing potential deadlock or
starvation.
Similar code pattern can be found at:
Line: 135, File: "org/apache/hadoop/hbase/regionserver/SplitRequest.java"
==========================================
=========================
Case 2:
Line: 252, File:
"org/apache/hadoop/hbase/regionserver/wal/SequenceFileLogReader.java"
{noformat}
try {
Field fEnd = SequenceFile.Reader.class.getDeclaredField("end");
fEnd.setAccessible(true);
end = fEnd.getLong(this.reader);
} catch(Exception e) { /* reflection fail. keep going */ }
{noformat}
The caught Exception seems to be too general.
While reflection-related errors might be harmless, the try block can throw
other exceptions including "SecurityException", "IllegalAccessException", etc.
Currently
all those exceptions are ignored. Maybe
the safe way is to ignore the specific reflection-related errors while logging
and
handling other types of unexpected exceptions.
==========================================
=========================
Case 3:
Line: 148, File: "org/apache/hadoop/hbase/HBaseConfiguration.java"
{noformat}
try {
if (Class.forName("org.apache.hadoop.conf.ConfServlet") != null) {
isShowConf = true;
}
} catch (Exception e) {
}
{noformat}
Similar to the previous case, the exception handling is too general. While
ClassNotFound error might be the normal case and ignored, Class.forName can
also throw other exceptions (e.g., LinkageError) under some unexpected and rare
error cases. If that happens, the error will be lost. So maybe change it to
below:
{noformat}
try {
if (Class.forName("org.apache.hadoop.conf.ConfServlet") != null) {
isShowConf = true;
}
} catch (LinkageError e) {
LOG.warn("..");
// handle linkage error
} catch (ExceptionInInitializerError e) {
LOG.warn("..");
// handle Initializer error
} catch (ClassNotFoundException e) {
LOG.debug("..");
// ignore
}
{noformat}
==========================================
=========================
Case 4:
Line: 163, File: "org/apache/hadoop/hbase/client/Get.java"
{noformat}
public Get setTimeStamp(long timestamp) {
try {
tr = new TimeRange(timestamp, timestamp+1);
} catch(IOException e) {
// Will never happen
}
return this;
}
{noformat}
Even if the IOException never happens right now, is it possible to happen in
the future due to code change?
At least there should be a log message. The current behavior is dangerous since
if the exception ever happens
in any unexpected scenario, it will be silently swallowed.
Similar code pattern can be found at:
Line: 300, File: "org/apache/hadoop/hbase/client/Scan.java"
==========================================
=========================
Case 5:
Line: 207, File: "org/apache/hadoop/hbase/util/JVM.java"
{noformat}
if (input != null){
try {
input.close();
} catch (IOException ignored) {
}
}
{noformat}
Any exception encountered in close is completely ignored, not even logged.
In particular, the same exception scenario was handled differently in other
methods in the same file:
Line: 154, same file
{noformat}
if (in != null){
try {
in.close();
} catch (IOException e) {
LOG.warn("Not able to close the InputStream", e);
}
}
{noformat}
Line: 248, same file
{noformat}
if (in != null){
try {
in.close();
} catch (IOException e) {
LOG.warn("Not able to close the InputStream", e);
}
}
{noformat}
==========================================
=========================
Case 6: empty handler for exception: java.io.IOException
Line: 312, File: "org/apache/hadoop/hbase/rest/RowResource.java"
{noformat}
} finally {
if (table != null) try {
table.close();
} catch (IOException ioe) { }
}
{noformat}
IOException is completely ignored. This behavior is inconsistent with the same
code snippet at line 249 in the same file, where the IOExceptions was logged:
{noformat}
} finally {
if (table != null) try {
table.close();
} catch (IOException ioe) {
LOG.debug("Exception received while closing the table", ioe);
}
}
{noformat}
==========================================
=========================
Case 7:
Line: 95, File:
"org/apache/hadoop/hbase/master/handler/EnableTableHandler.java"
{noformat}
try {
this.assignmentManager.getZKTable().removeEnablingTable(tableName,
true);
} catch (KeeperException e) {
// TODO : Use HBCK to clear such nodes
LOG.warn("Failed to delete the ENABLING node for the table " +
tableName
+ ". The table will remain unusable. Run HBCK to manually fix
the problem.");
}
{noformat}
The log message in the exception handler and the comment seem to suggest that
such nodes should be cleared using HBCK.
==========================================
=========================
Case 8:
Line: 463, File: "org/apache/hadoop/hbase/client/ClientScanner.java"
{noformat}
try {
this.caller.callWithRetries(callable);
} catch (IOException e) {
// We used to catch this error, interpret, and rethrow. However, we
// have since decided that it's not nice for a scanner's close to
// throw exceptions. Chances are it was just an UnknownScanner
// exception due to lease time out.
}
{noformat}
Currently the handler is empty because it may be caused by "just an
UnknownScanner exception".
But what if it has other causes? Maybe the catch block can differentiate the
exception into
different causes, ignoring the ones caused by UnknownScanner while handle
others differently?
==========================================
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