RFR: 8269934: RunThese24H.java failed with EXCEPTION_ACCESS_VIOLATION in java_lang_Thread::get_thread_status

[Daniel D.Daugherty]

On Wed, 28 Jul 2021 10:03:10 GMT, David Holmes <dholmes at openjdk.org> wrote:

> If a thread is attaching via JNI and has not yet created its Thread object it can be caught in a ThreadSnapshot during a thread dump (VM_DumpThreads) of all threads**, and the threadObj() will be NULL, so we can't pass it to get_thread_status().
> 
> ** JMM dumpThreads API
> 
> The initial fix simply checks for a NULL threadObj() and reports thread status NEW in that case.
> 
> Alternatively we could filter the attaching thread out completely in VM_DumpThreads::doit by expanding:
> 
>       if (jt->is_exiting() ||
>           jt->is_hidden_from_external_view())  {
>         // skip terminating threads and hidden threads
>         continue;
>       }
> 
> to also check jt->is_attaching_via_jni().
> 
> Note that higher-level code already filters out ThreadSnapshots with NULL threadObj() anyway so we could go either way.
> 
> Testing: manual hacks - see bug report.
>   - tier 1-3 sanity testing
> 
> Thanks,
> David

Nice catch!

I'm always happy when we find a reason for one of these 24 hour
stress test failures.

Thumbs up! Your call on whether to change the code as I mentioned
in my other comment.

@sspitsyn - It would be great to have a Serviceability person chime in on this review...

src/hotspot/share/services/threadService.cpp line 879:

> 877:   // If thread is still attaching then threadObj will be NULL.
> 878:   _thread_status = threadObj == NULL ? JavaThreadStatus::NEW
> 879:                                      : java_lang_Thread::get_thread_status(threadObj);

I like the use of `JavaThreadStatus::NEW` here.

Since L867 creates the _threadObj OopHandle, do you want to change both
uses of `threadObj` to `_threadObj()`? Is that still how we fetch the oop from
an OopHandle? Or even use `threadObj()`... Then we don't have to reason
about whether the `threadObj` oop is still good...

-------------

Marked as reviewed by dcubed (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/4921