3-nd round RFR 6471769: Error: assert(_cur_stack_depth == count_frames(), "cur_stack_depth out of sync")

Thu, 27 Feb 2014 19:51:06 -0800 

Please, review the fix for:
  https://bugs.openjdk.java.net/browse/JDK-6471769


Open webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2014/hotspot/6471769-JVMTI-DEPTH.3

Summary:

  It is another attempt to fix the JTREG com/sun/jdi tests regression
  discovered in the first round change.
The fix is to avoid lock synchronization at safepoints(jvmtiEventController.cpp). 
  Thanks to Dan for catching the problem in the 2-nd round of review!

Testing:
  All tests are passed: nsk.jvmti, nsk.jdi, nsk.jdwp, JTreg com/sun/jdi


Thanks,
Serguei


On 2/27/14 2:00 PM, serguei.spit...@oracle.com wrote:

On 2/27/14 1:03 PM, serguei.spit...@oracle.com wrote:

On 2/27/14 12:28 PM, serguei.spit...@oracle.com wrote:

Dan,

Thank you a lot for reviewing this!

On 2/27/14 11:09 AM, Daniel D. Daugherty wrote:

On 2/27/14 1:25 AM, serguei.spit...@oracle.com wrote:

Please, review the fix for:
  https://bugs.openjdk.java.net/browse/JDK-6471769


Open webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2014/hotspot/6471769-JVMTI-DEPTH.2 

src/share/vm/runtime/vm_operations.hpp
    No comments.

src/share/vm/prims/jvmtiEnvBase.hpp
    No comments.

src/share/vm/prims/jvmtiEnv.cpp
    No comments.

src/share/vm/prims/jvmtiEnvThreadState.cpp
    No comments.

src/share/vm/prims/jvmtiEventController.cpp
    JvmtiEventController::set_frame_pop() is called by
    JvmtiEnvThreadState::set_frame_pop() which is called by
    JvmtiEnv::NotifyFramePop().

    The "MutexLocker mu(JvmtiThreadState_lock)" in
    JvmtiEventController::set_frame_pop() protected the work
    done by JvmtiEventControllerPrivate::set_frame_pop():

      ets->get_frame_pops()->set(fpop);
recompute_thread_enabled(ets->get_thread()->jvmti_thread_state());


Your check is the right thing to do, thanks!
I had to explain this more clearly in this 2-nd review request.

The approach I've taken here is that all this code paths are executed
on the target thread or at a safepoint.

It is true for all 3 functions:
  set_frame_pop(), clear_frame_pop() and clear_to_frame_pop().

And the updated assert guards ensure that it is the case.
It could be a good idea to add a No_Safepoint_Verifier for PopFrame() and NotifyFramePop() to make sure the current/target thread does not go to safepoint until it is returned from 
update_for_pop_top_frame() and set_frame_pop() correspondingly.
A No_Safepoint_Verifier can be also needed in the JvmtiExport::post_method_exit(). 

These are all places where these functions are called:
prims/jvmtiEnv.cpp: state->env_thread_state(this)->set_frame_pop(frame_number); // JvmtiEnv::NotifyFramePop() prims/jvmtiExport.cpp: ets->clear_frame_pop(cur_frame_number); // JvmtiExport::post_method_exit() prims/jvmtiThreadState.cpp: ets->clear_frame_pop(popframe_number); // JvmtiThreadState::update_for_pop_top_frame()
The function JvmtiEnvThreadState::clear_to_frame_pop() is never called now. 

There is still a concern about recompute_thread_enabled().
If it is normally always protected with the JvmtiThreadState_lock
then the approach above is not going to work.
I'm trying to check this now.


Dan,

I came to a conclusion that these 3 functions still must be protected
by the JvmtiThreadState_lock when they are called out of a safepoint.
It is a little bit ugly but has to be safe though.

Please, let me know if you see eny problems with that.
I'll send a new webrev soon.

Thanks,
Serguei




Thanks,
Serguei




Thanks,
Serguei







    Since multiple threads can call JVM/TI NotifyFramePop() on the
    same target thread, what keeps the threads from messing with
    the list of frame pops simultaneously or messing with the
    thread enabled events bits in parallel?

    I suspect that this might also be an issue for
    JvmtiEventController::clear_frame_pop() and
    JvmtiEventController::clear_to_frame_pop() also.

src/share/vm/prims/jvmtiThreadState.cpp
    No comments.

Dan




Summary:
It is the 2-nd round of review because the JTREG com/sun/jdi tests discovered a regression in the first round change. The issue was in the JvmtiEventController::clear_frame_pop() 
  lock synchronization that is not allowed at safepoints.
As a result I've changed the JvmtiEnv::NotifyFramePop to use a VM operation for safety. Also, I've removed the lock synchronization from the 3 impacted JvmtiEventController:: functions: set_frame_pop(), clear_frame_pop() and clear_to_frame_pop(). 

Testing:
  In progress: nsk.jvmti, nsk.jdi, nsk.jdwp, JTreg com/sun/jdi


Thanks,
Serguei


On 2/25/14 12:43 PM, serguei.spit...@oracle.com wrote:

Please, review the fix for:
  https://bugs.openjdk.java.net/browse/JDK-6471769


Open webrev:
http://cr.openjdk.java.net/~sspitsyn/webrevs/2014/hotspot/6471769-JVMTI-DEPTH.1 

Summary:

  This is another Test Stabilization issue.
  The fix is very similar to other JVMTI stabilization fixes.
It is to use safepoints for updating the PopFrame data instead of relying on the suspend equivalent condition mechanism (JvmtiEnv::is_thread_fully_suspended()) 
  which is not adequate from the reliability point of view.

Testing:
  In progress: nsk.jvmti, nsk.jdi, nsk.jdwp, JTreg com/sun/jdi


Thanks,
Serguei

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