[9] RFR(S): 8075214: SIGSEGV in nmethod sweeping

David Holmes david.holmes at oracle.com
Thu Mar 26 00:59:38 UTC 2015

Hi Tobias,

As per Mikaels comments there are a lot of issues with this code. The 
Java exception handling is one part. Overall it is a hybrid mix of the 
other ways we create threads in the VM. See CompileBroker::make_thread 
(which you may have used as a partial template) but note the exception 
handling and that Thread::start is called while the Threads_lock is held 
(which is not the case in the WB code - old or new - which may address 
the other issue in JDK-8072377).

Please cc me in any reply as I'm not this list.


> Hi,
> please review the following patch.
> https://bugs.openjdk.java.net/browse/JDK-8075214
> http://cr.openjdk.java.net/~thartmann/8075214/webrev.00/
> Problem:
> The test uses the Whitebox API to enforce sweeping by creating and starting a 'CodeCacheSweeperThread'. During creation of the thread, the interpreter crashes in j.l.ThreadGroup.add(Thread t) [1] while executing a subtype check to validate that 't' is a subtype of j.l.Thread [2]. The problem is that we pass 'JavaThread->threadObj()' to 'ThreadGroup.add' which is invalid due to a GC that moved the object. The GC does not know about the thread because it was not yet added to the threads list and therefore does not update the oop.
> Solution:
> Instead of calling 'JavaThread::allocate_threadObj', the initialization is moved to the caller to make sure that setting the thread oop is done together with adding the thread to the threads list. I also fixed the missing oom handling described as one of the problems in JDK-8072377 [3].
> Testing:
> - 1k runs of failing testcase
> - JPRT
> Thanks,
> Tobias
> [1] http://hg.openjdk.java.net/jdk9/hs-comp/jdk/file/tip/src/java.base/share/classes/java/lang/ThreadGroup.java#l896
> [2] see '__ gen_subtype_check' in 'TemplateTable::aastore'
> [3] https://bugs.openjdk.java.net/browse/JDK-8072377

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