[RFR] 8196969: JTreg Failure: serviceability/sa/ClhsdbJstack.java causes NPE

[Chris Plummer]

On 10/2/19 1:57 AM, Severin Gehwolf wrote:
> On Wed, 2019-10-02 at 10:39 +0200, Severin Gehwolf wrote:
>> On Tue, 2019-10-01 at 12:51 -0700, Chris Plummer wrote:
>>> Hi Severin,
>>>
>>> Sorry, this is not an area that I have any expertise in. However, I did
>>> confirm that it fixes the NPE I was seeing with JShellHeapDumpTest.java,
>>> which brings up a question. You said this happens with -Xcomp, but I was
>>> never using -Xcomp. Might it also be triggered without -Xcomp?
>> Yes, as soon as C1/C2 kick in you might be seeing the issue. In fact, I
>> had one reproducer which triggered the issue quite reliably which
>> didn't use -Xcomp explicitly. Nevertheless, certain methods got JIT
>> compiled soon and the issue surfaced. You should be able to verify by
>> adding -XX:+PrintCompilation to the host program and/or comparing it to
>> -Xint runs.
>>
>> TLDR; -Xcomp helps reproducing the issue on smaller test cases, but
>> isn't essential in the general case.
> On second thought, I haven't investigated whether running the SA on a
> heap dump triggers the issue as well. There might be another code path
> not covered with this patch. If there still is, it might be a similar,
> but slightly different bug.
So  you are saying your fix here is for when producing the heap dump, 
but parsing the heap dump might also have a similar issue? I think we 
are not seeing any issue with the parsing. My new 
HeapDumpTestWithActiveProcess.java test used to reproduce the NPE when 
dumping the heap, and your fix has resolved that issue. The test then 
goes on to dump all the stacks in the heap dump, so I think if there was 
a problem we would have seen it.

Chris
>
> Thanks,
> Severin
>