URGENT RFR (S): fix for Test8004741.java crashes with SIGSEGV in JDK10-hs nightly (8185273)

[Roman Kennke]

Hi Dan,

You could also do_thread() on the VMThread, and let the ThreadClosurer
filter it. I believe the ThreadClosure in safepoint.cpp (currently only
consumer) already filters it. This would make it consistent with
Threads::possibly_parallel_oops_do() (and infact, that latter method
could just use the new Threads::parallel_java_threads_do() but this is
beyond the scope). I leave that to you to decide though.

I'd also include the fix for assert_all_threads_claimed() because it's
related (and the cause for me not noticing this slip). But that is up to
you too. ;-)

In other words, thumbs up, unless you want to add the above points.

And sorry for making such a mess!

Roman

> Greetings,
>
> I have a fix for the following P1 JDK10-hs integration_blocker bug:
>
>     8185273 Test8004741.java crashes with SIGSEGV in JDK10-hs nightly
>     https://bugs.openjdk.java.net/browse/JDK-8185273
>
> The fix is 2 lines and the comment describing the fix is 4 lines:
>
> src/share/vm/runtime/thread.cpp:
>
> L3388: void Threads::parallel_java_threads_do(ThreadClosure* tc) {
> <snip>
> L3395:   // This function is used by ParallelSPCleanupTask in
> safepoint.cpp
> L3396:   // for cleaning up JavaThreads, but we have to keep the
> VMThread's
> L3397:   // _oops_do_parity field in sync so we don't miss a parallel
> GC on
> L3398:   // the VMThread.
> L3399:   VMThread* vmt = VMThread::vm_thread();
> L3400:   (void)vmt->claim_oops_do(true, cp);
>
> I'm also including some new logging for the VMThread (tag == 'vmthread')
> that came in useful during this bug hunt. Lastly, I've fixed a few minor
> typos that I ran across in the areas where I was hunting.
>
> Webrev URL: http://cr.openjdk.java.net/~dcubed/8185273-webrev/0/
>
> There's lots of discussion in the bug. The evaluation comment that I
> added
> on Sunday, July 30 is probably the most complete and hopefully the
> most clear.
>
> For context, here's the webrev for 8180932 and another bug fix:
>
> http://cr.openjdk.java.net/~rkennke/8180932/webrev.18/
> http://cr.openjdk.java.net/~rkennke/8185102/webrev.01/
>
>
> Testing:
>   - JPRT
>   - Test8004741.java has been running in a forever loop with 'fastdebug'
>     bits (17200+ iterations) and 'slowdebug' bits (13400+ iterations)
>
> Comments, questions and feedback are welcome.
>
> Dan
>
> P.S.
> Roman and I were also thinking about updating
> Threads::assert_all_threads_claimed() to verify
> that the VMThread is also claimed... Obviously
> that's not part of the current patch...