RFR(S): 7069863: G1: SIGSEGV running SPECjbb2011 and -UseBiasedLocking

Vladimir Kozlov vladimir.kozlov at oracle.com
Fri Jul 29 17:15:12 UTC 2011


Why you did not add failed_to_reserve_as_requested() to ReservedSpace() as I 
asked? It is missing there after the code which handle wrong alignment.


John Cuthbertson wrote:
> Hi Everyone,
> A new webrev based upon the feed back from Vladimir can be found at: 
> http://cr.openjdk.java.net/~johnc/7069863/webrev.1/
> I'm looking for one more reviewer.
> Thanks,
> JohnC
> On 07/27/11 12:06, Vladimir Kozlov wrote:
>> g1CollectedHeap.cpp:
>>   // When compressed oops are used the preferred heap base is calculated
>>   // by subtracting the requested size from the 32Gb boundary and using
>>   // the result as the base address for heap reservation. If the size is
>>   // not aligned to HeapRegion::GrainBytes passed into the 
>> ReservedHeapSpace
>>   // constructor then the base of the actual reserved heap may end up
>>   // differing from the requested base address. If this happens then we
>>   // could end up using a non-optimal compressed oops mode.
>> virtualspace.cpp:
>>  213   // prefix_align == suffix_align).
>>                        ^ prefix_align < suffix_align
>> ReservedSpace::ReservedSpace() also misses the call to 
>> failed_to_reserve_as_requested() after the code which handle wrong 
>> alignment.
>> Add assert into ReservedSpace::initialize()
>>   // Assert that if noaccess_prefix is used, it is the same as alignment.
>>   assert(noaccess_prefix == 0 ||
>>          noaccess_prefix == alignment, "noaccess prefix wrong");
>> Why we have next code? Should we do this alignment adjustment at the 
>> beginning of the method?
>> 355   _alignment = MAX2(alignment, (size_t) os::vm_page_size());
>> Vladimir
>> John Cuthbertson wrote:
>>> Hi Everyone,
>>> Can I have a couple of volunteers look over these changes - the 
>>> webrev can be found at: 
>>> http://cr.openjdk.java.net/~johnc/7069863/webrev.0/
>>> The issue was caused by an implicit null check in generated code not 
>>> firing. The implicit null check did not trap as a result of a 
>>> mismatch between the compressed oops mode and the calculated heap 
>>> base. Also the page below heap base was not being protected. The 
>>> mismatch between the compressed oops mode and heap base was the 
>>> result of the G1 heap initialization code passing in a total heap 
>>> size (G1 heap and perm) that was not a multiple of the alignment 
>>> passed into the ReservedSpace constructor. Hence the preferred heap 
>>> base address was not correctly aligned causing the ReservedSpace to 
>>> be allocated at an address other than the preferred heap base. The 
>>> page below the heap base was not protected because the G1 heap 
>>> initialization code was calling the wrong ReservedSpace constructor.
>>> Testing: the failing test case; various small tests with various 
>>> collectors, large heaps, and +PrintCompressedOopsMode.
>>> Many thanks to Vladimir and Igor for helping to diagnose the issue.
>>> Thanks,
>>> JohnC

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