RFR(S) 8176887: SIGSEGV in AOTCodeHeap::next when using specific configuration

[Igor Veresov]

Thanks, Coleen!

igor

> On Apr 10, 2017, at 1:22 PM, coleen.phillimore at oracle.com wrote:
> 
> 
> 
> On 4/10/17 3:48 PM, Igor Veresov wrote:
>> So… I’m ok to assume that you’re ok with this fix for the time being?
> 
> If these MethodCounters aren't added to the CDS archive, then the vptr only adds space and I think it's ok for now.
> Coleen
> 
>> 
>> igor
>> 
>>> On Apr 7, 2017, at 3:43 PM, Igor Veresov <igor.veresov at oracle.com <mailto:igor.veresov at oracle.com>> wrote:
>>> 
>>>> 
>>>> On Apr 7, 2017, at 2:36 PM, coleen.phillimore at oracle.com <mailto:coleen.phillimore at oracle.com> wrote:
>>>> 
>>>> 
>>>> 
>>>> On 4/7/17 5:33 PM, Igor Veresov wrote:
>>>>>> On Apr 7, 2017, at 1:29 PM, Vladimir Kozlov <vladimir.kozlov at oracle.com <mailto:vladimir.kozlov at oracle.com>> wrote:
>>>>>> 
>>>>>> This could be good fix for JDK 9.
>>>>>> 
>>>>>> Are you sure that functions called for Metadata scan will not barf on MethodCounters?
>>>>> Yes, there shouldn’t be any problems. In the context of class redefinition it calls mark_on_stack(), which is empty by default except for Method and ConstantPool.
>>>>> 
>>>>>> You need also ask Runtime group to look on this change.
>>>>> CCing the runtime mail list. Guys, any objections to making MethodCounters a Metadata ?
>>>> 
>>>> If you make MethodCounters inherited by Metadata it will have a vptr.  It doesn't otherwise.
>>> 
>>> Yes, but I’d have to have some type id to filter them out anyway (if they are in an array with other metaspace objects), having a vtbl seems like an equivalent solution.
>>> 
>>>>> 
>>>>>> When fixing 8173794 I missed this case (MethodCounters*). We should not put them into metaspace_got array since GC don't need to process them. And they increase metaspace_got array significantly.
>>>>>> 
>>>>>> For 10 we should fix JAPTC code - metaspace_got array should contain only Klass* pointers. May be to add a separate array since extLinkageGOTContainer may not right for MethodCounters*.
>>>>> 
>>>>> In the context of class redefinition the scan is actually interested only in methods, rather than classes. Going forward, yes, it would probably be better if we had separate GOT arrays for each MetaspaceObj subtype, so that we can separate Methods out and scan only them.
>>>> 
>>>> Can you have a special array for Method*s?
>>> 
>>> Yes, that’s what would be best to do in the future. But it is a substantially bigger change, I’m not sure it would be appropriate for 9 at this point. 
>>> 
>>> igor
>>> 
>>>> Coleen
>>>> 
>>>>> igor
>>>>> 
>>>>>> Thanks,
>>>>>> Vladimir
>>>>>> 
>>>>>> On 4/7/17 11:55 AM, Igor Veresov wrote:
>>>>>>> The problem here is that AOTCodeHeap::got_metadata_do() iterates over the _metaspace_got array assuming that the array contains Metadata*, indeed the array is declared as such. However it also happens to contain MethodCounters*, and MethodCounters is not Metadata, but MetaspaceObj. The simplest and minimal risk solution is to make MethodCounters a subclass of Metadata (we’d like to have this fix in jdk9).
>>>>>>> 
>>>>>>> 
>>>>>>> Webrev: http://cr.openjdk.java.net/~iveresov/8176887/webrev.00/ <http://cr.openjdk.java.net/%7Eiveresov/8176887/webrev.00/>
>>>>>>> JBS: https://bugs.openjdk.java.net/browse/JDK-8176887 <https://bugs.openjdk.java.net/browse/JDK-8176887>
>>>>>>> 
>>>>>>> Thanks!
>>>>>>> igor
>> 
> 

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