IV50065: UNSYNCHRONIZED CONCURRENT ACCESSES TO ARRAYLIST CAUSES JVM CRASH

APAR status

• Closed as program error.

Error description

• Error Message: The JVM raises a GPF or crashes during object
  allocation or garbage collection, if multiple threads have tried
  to use an ArrayList object without synchronization. Post-mortem
  analysis reveals that the value in the object's "size" field and
  the actual length of the underlying array have become
  inconsistent, which can cause heap corruption.
  .
  Stack Trace: Native call stack:
      MM_ParallelScavenger::scavengeRememberedSetList+0x98
      MM_ParallelScavenger::workThreadGarbageCollect+0x38
      MM_Dispatcher::run+0x35
      MM_ParallelScavenger::scavenge+0x6e
      MM_Scavenger::masterThreadGarbageCollect+0xc7
      MM_Scavenger::internalGarbageCollect+0x71d
      MM_ParallelScavenger::internalGarbageCollect+0x1f
      MM_Collector::garbageCollect+0x214
      MM_MemorySubSpaceSemiSpace::allocationRequestFailed+0x133
      MM_MemorySubSpaceGeneric::allocateTLH+0x58
      MM_TLHAllocationInterface::refresh+0x27c
      MM_TLHAllocationInterface::allocateFromTLH+0xab
      MM_TLHAllocationInterface::allocateObject+0xfe
      MM_MixedObjectAllocationModel::allocateMixedObject+0xb4
      J9AllocateObject+0xd5
      jitNewObject+0xb1b
  .
  

Local fix

• This problem can be avoided with the
  -Xjit:exclude={java/util/ArrayList.*},dontInline={java/util/Arra
  yList.*} option. The program should then throw an exception
  instead of quietly corrupting the heap. It is the developer's
  responsibility to ensure that ArrayList accesses are
  synchronized, according to the API. Note that the workaround may
  cause a noticeable performance degradation.
  

Problem summary

• The problem is caused when an ArrayList object is modified by
  multiple threads at the same time. This will normally cause an
  ArrayIndexOutOfBoundsException but the JIT compiler is
  incorrectly removing the exception check.
  

Problem conclusion

• This defect will be fixed in:
  7.0.0 SR6
  6.0.1 SR7
  6.0.0 SR15
  .
  The JIT compiler has been updated to generate bounds check for
  ArrayList methods correctly. A new
  -Xjit:disableRecognizedMethods option has been introduced to
  suppress similar optimizations.
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  PI09153

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R260 PSY

     UP

• R600 PSY

     UP