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

[Severin Gehwolf]

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.

Thanks,
Severin