Crash on super large heap size using CMS and it's fix

John Cuthbertson john.cuthbertson at oracle.com
Wed Sep 12 18:39:06 UTC 2012


Hi Bengt,

Thanks for volunteering. I was until I saw your message.

Hal: Great catch.

We should probably change the other casts/shifts  in 
heapRegionRemSet.cpp and concurrentMark.cpp at the same time

./share/vm/gc_implementation/g1/heapRegionRemSet.cpp
     _max_fine_entries = (size_t)(1 << max_entries_log);

./share/vm/gc_implementation/g1/concurrentMark.cpp
   assert(((size_t)_bm.size() * (size_t)(1 << _shifter)) == _bmWordSize,

even though they shouldn't overflow.

JohnC

On 9/12/2012 12:50 AM, Bengt Rutisson wrote:
>
> Hi Hal Mo,
>
> Nice catch!
>
> I filed "7197906:BlockOffsetArray::power_to_cards_back() needs to 
> handle > 32 bit shifts" to track this issue. I can help you shepherd 
> this fix in.
>
> Thanks,
> Bengt
>
>
> On 2012-09-12 03:22, Jianhao Mo wrote:
>> Hi all,
>>
>> This is Hal Mo<kungu.mjh at taobao.com <mailto:kungu.mjh at taobao.com>> 
>> from Alibaba Group(with OCA).
>>
>> Our hadoop namenode crashed, when we set the heap size to 135G using 
>> CMS GC.
>> Attached please find the crash log(hs_err_pid.log).
>>
>> I can steadily reproduce the crash on a test machine with 190G 
>> physical memory, by a simple command:
>> $ java -Xmx135g -XX:+UseConcMarkSweepGC
>>
>> Then I build a debug jvm and use gdb to debug the problem.
>>
>> call stack
>>
>> C  [libc.so.6+0x7a9b0]  memset+0x40
>> V  [libjvm.so+0x2b6c42] 
>>  BlockOffsetArray::set_remainder_to_point_to_start_incl(unsigned 
>> long, unsigned long, bool)+0xce
>> V  [libjvm.so+0x2b7043] 
>>  BlockOffsetArray::set_remainder_to_point_to_start(HeapWord*, 
>> HeapWord*, bool)+0x71
>> V  [libjvm.so+0x2b728d] 
>>  BlockOffsetArray::BlockOffsetArray(BlockOffsetSharedArray*, 
>> MemRegion, bool)+0x9f
>> V  [libjvm.so+0x3c089f] 
>>  BlockOffsetArrayNonContigSpace::BlockOffsetArrayNonContigSpace(BlockOffsetSharedArray*, 
>> MemRegion)+0x37
>> V  [libjvm.so+0x3be56f] 
>>  CompactibleFreeListSpace::CompactibleFreeListSpace(BlockOffsetSharedArray*, 
>> MemRegion, bool, FreeBlockDictionary::DictionaryChoice)+0x9b
>> V  [libjvm.so+0x3fd2e1] 
>>  ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(ReservedSpace, 
>> unsigned long, int, CardTableRS*, bool, 
>> FreeBlockDictionary::DictionaryChoice)+0x1df
>> V  [libjvm.so+0x4dc03e]  GenerationSpec::init(ReservedSpace, int, 
>> GenRemSet*)+0x37c
>> V  [libjvm.so+0x4ced40]  GenCollectedHeap::initialize()+0x510
>> V  [libjvm.so+0x7c23c3]  Universe::initialize_heap()+0x31d
>> V  [libjvm.so+0x7c27ec]  universe_init()+0xa6
>> V  [libjvm.so+0x5056e2]  init_globals()+0x34
>> V  [libjvm.so+0x7ac926]  Threads::create_vm(JavaVMInitArgs*, bool*)+0x23a
>> V  [libjvm.so+0x53f3d4]  JNI_CreateJavaVM+0x7a
>>
>> in function BlockOffsetArray::set_remainder_to_point_to_start_inc, 
>> inside the for loop:
>>     size_t reach = start_card - 1 + (power_to_cards_back(i+1) - 1);
>> when i = 7, the value of reach was 0. then the loop could not break, and
>>     _array->set_offset_array(start_card_for_region, reach, offset, 
>> reducing);
>> accessed the wrong address, and crashed.
>>
>> the root cause was
>> static size_t power_to_cards_back(uint i) {
>>     return (size_t)(1 << (LogBase * i));
>> }
>> the literal 1 is a 32bit int, and 1<<32 overflow.
>>
>>
>> Here was my fix(has been tested), also found in attached file 
>> cms_large_heap_crash.patch
>>
>> +++ b/src/share/vm/memory/blockOffsetTable.hpp
>> @@ -289,7 +289,7 @@
>> };
>>
>> static size_t power_to_cards_back(uint i) {
>> - return (size_t)(1 << (LogBase * i));
>> + return (size_t)1 << (LogBase * i);
>> }
>> static size_t power_to_words_back(uint i) {
>> return power_to_cards_back(i) * N_words;
>>
>> Contributed-by: Hal Mo <kungu.mjh at taobao.com 
>> <mailto:kungu.mjh at taobao.com>>
>>
>> Similar situation also found in G1, but the size is mega(2^20) based. 
>> 2^(32+20) is too large to overflow.
>>
>> Krystal remind me, this changeset cover the same code, 
>> http://hg.openjdk.java.net/hsx/hotspot-gc/hotspot/rev/c3a720eefe82  .
>> I do not  build it on visual studio, someone please help to review 
>> the compatibility with VS.
>>
>> Regards,
>>
>> Hal
>
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