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From "ZhaoYang (Jira)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-15726) buffer pool may NPE with concurrent release
Date Tue, 14 Apr 2020 12:05:00 GMT
ZhaoYang created CASSANDRA-15726:
------------------------------------

             Summary: buffer pool may NPE with concurrent release
                 Key: CASSANDRA-15726
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15726
             Project: Cassandra
          Issue Type: Bug
            Reporter: ZhaoYang
            Assignee: ZhaoYang


This can be reproduced by running {{LongBufferPoolTest}}, 1 out 5 runs..
{code:java}
java.lang.NullPointerException
	at org.apache.cassandra.utils.memory.BufferPool$Chunk.access$1300(BufferPool.java:836)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.lambda$remove$1(BufferPool.java:716)
	at org.apache.cassandra.utils.memory.BufferPool$MicroQueueOfChunks.removeIf(BufferPool.java:460)
	at org.apache.cassandra.utils.memory.BufferPool$MicroQueueOfChunks.access$1500(BufferPool.java:304)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.remove(BufferPool.java:716)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.put(BufferPool.java:590)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.recycle(BufferPool.java:709)
	at org.apache.cassandra.utils.memory.BufferPool$Chunk.recycle(BufferPool.java:909)
	at org.apache.cassandra.utils.memory.BufferPool$Chunk.tryRecycle(BufferPool.java:903)
	at org.apache.cassandra.utils.memory.BufferPool$Chunk.release(BufferPool.java:896)
	at org.apache.cassandra.utils.memory.BufferPool$MicroQueueOfChunks.removeIf(BufferPool.java:465)
	at org.apache.cassandra.utils.memory.BufferPool$MicroQueueOfChunks.access$1500(BufferPool.java:304)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.addChunk(BufferPool.java:736)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.addChunkFromParent(BufferPool.java:725)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.tryGetInternal(BufferPool.java:691)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.tryGet(BufferPool.java:679)
	at org.apache.cassandra.utils.memory.BufferPool$LocalPool.access$000(BufferPool.java:518)
	at org.apache.cassandra.utils.memory.BufferPool.tryGet(BufferPool.java:120)             
         
	at org.apache.cassandra.utils.memory.LongBufferPoolTest$2.testOne(LongBufferPoolTest.java:497)
	at org.apache.cassandra.utils.memory.LongBufferPoolTest$TestUntil.call(LongBufferPoolTest.java:558)
	at org.apache.cassandra.utils.memory.LongBufferPoolTest$TestUntil.call(LongBufferPoolTest.java:538)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.lang.Thread.run(Thread.java:748)
{code}
The cause is that:
 * When evicting a normal chunk from a full MicroQueueOfChunks, local pool will try to remove
corresponding tiny chunks, via {{MicroQueueOfChunks#removeIf}}.
 * If matching tiny chunk is found, tiny {{chunk.release()}} is called immediately before
moving null chunk to the back of the queue.
 * Due to concurrent release from different threads, tiny {{chunk.release()}} may cause its
parent normal chunk, aka. the evicted chunk in #1, to be removed from local pool and causes
tiny pool to remove corresponding tiny chunks again in {{LocalPool#remove()}}.
 * In {{MicroQueueOfChunks#removeIf}}, due to previous in-progress {{removeIf}}, it throws
NPE as it violate MicroQueueOfChunks's assumption which requires null chunks to be put at
the back of queue.

 

| [patch|https://github.com/apache/cassandra/pull/537] | [CI|https://circleci.com/workflow-run/a97317a0-ef21-4c01-9a97-82eaf28d7faf]|
The fix to put null chunks to the back of queue before releasing any chunks.



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