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List:       openjdk-hotspot-runtime-dev
Subject:    Re: RFR(S) : 8029381 : assert(is_method_type()) failed: bad cast
From:       Coleen Phillimore <coleen.phillimore () oracle ! com>
Date:       2014-05-30 21:46:42
Message-ID: 5388FC42.3080503 () oracle ! com
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This fix looks good to me too (I've seen it already), and I agree, it 
doesn't look like it would be testable.

Coleen

On 5/30/14, 5:34 PM, Vladimir Kozlov wrote:
> CC to runtime.
>
> Looks good to me. I added 'noreg-hard' (no regression test) label to 
> the bug report. You can add more to my comment about not having the test.
>
> Thanks,
> Vladimir
>
> On 5/30/14 1:36 PM, David Chase wrote:
>>
>> bug: https://bugs.openjdk.java.net/browse/JDK-8029381
>> webrev: http://cr.openjdk.java.net/~drchase/8029381/webrev.00/
>>
>> Problem: about once per month this assertion would fail in SQE testing,
>> usually running one of the streams-related tests with -Xcomp.
>>
>>    ciMethodType* as_method_type() {
>>      assert(is_method_type(), "bad cast");
>>      return (ciMethodType*)this;
>>    }
>>
>> The cause was a failure to check "f1" before accessing constant pool
>> cache entries, and when competing threads raced, junk would be observed.
>> This would only matter for invokedynamic -- the combo of needing both
>> invokedynamic and multiple threads racing in the cpcache meant that
>> it was observed in the streams tests (even a test hand-crafted to 
>> make this
>> failure occur would only fire about once ever 5000 times, and with 
>> -Xcomp that
>> meant this was painfully slow).
>>
>> The fix is to insert the check into the access macros themselves
>> (for both method_type and appendix -- same problem for invokedynamic)
>> and to remove the now-redundant checks from those places where it had
>> been done right already.
>>
>> Testing:
>>
>> that bug was fixed: distilled the bug trigger out of the streams 
>> tests into something that
>> did nothing by fork-joins into bug triggers.  Then modified hotspot 
>> to repeat one side of
>> the race 1000 times in the event of an invokedynamic.  Observed 
>> failures once per 50 runs
>> in this case, applied fix, observed no failures in 2600 runs.
>>
>> that no harm was done:
>> jtreg of hotspot/compiler
>> jtreg of jdk/{jdk,vm}, no flags and -Xcomp
>> jprt of hotspot
>>
>> Question -- should test test case be added?  It practically never 
>> fails even when the
>> bug is unfixed; without tweaking hotspot, it tells you practically 
>> nothing at all.  Checking
>> the fix took all night.
>>

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