Re: RFR JDK-8195639: [Graal] nsk/jvmti/PopFrame/popframe009 fail with Graal in -Xcomp

[serguei.spit...@oracle.com]

Hi Dean, Thank you a lot for looking at this! Just a couple of points from me (it is up to Alex to provide a full answer). I think, Alex in this RFR missed to tell that we knew about this issue that an incorrect frame will be popped. But after some discussion we decided to file a separate issue on this. Alex wanted to create a good stand-alone test case demonstrating this problem before filing it.   Now, as I can see, the JDK-8195635 looks very close to a bug that we wanted to file. The only difference is that our scenario includes the SharedRuntime::resolve_static_call_C instead of the JavaCallWrapper::JavaCallWrapper as a helper for Java method invocation. If I understand corrctly (Alex will fix me if needed), the jtreg test we used to chase this issue did not catch a problem with the HotSpotJVMCIRuntime.adjustCompilationLevel. The suggested fix was to fix the mismatch in the TieredThresholdPolicy::even with the comment in the interpreter code: nmethod* InterpreterRuntime::frequency_counter_overflow(JavaThread* thread, address branch_bcp) {     . . .   if (nm != NULL && thread->is_interp_only_mode()) {     // Normally we never get an nm if is_interp_only_mode() is true, because     // policy()->event has a check for this and won't compile the method when     // true. However, it's possible for is_interp_only_mode() to become true     // during the compilation. We don't want to return the nm in that case     // because we want to continue to execute interpreted.     nm = NULL;   } > So I think the fix needs to be in code like SharedRuntime::resolve_static_call_C(), > where it returns get_c2i_entry() if is_interp_only_mode() is true. I'm not sure, the adding this condition and returning the get_c2i_entry() is always correct. We need some help from the Compiler team to make it right. BTW, the interp_only_mode has been enabled only when some interp_only events are enabled. It is not set by either PopFrame or ForceEarlyReturn. But the popframe009 test enables single stepping, so we wanted to make this part right. Thanks, Serguei On 11/26/18 16:05, dean.l...@oracle.com wrote: How does this solve the problem of HotSpotJVMCIRuntime.adjustCompilationLevel being called? I don't think this fix is the right approach.  Doesn't is_interp_only_mode() only apply to the current thread?  I don't think it's safe to assume no compiles will happen in other threads, or that a method call target is not already compiled, because as far as I can tell, JVMTI only deoptimizes the active frames.  The bug report describes a case where the caller has been deoptimized while resolving a call.  I don't see how this fix prevents the target from being a previously compiled method.  But we do need to make sure not to call into compiled code, so I think the fix needs to be in code like SharedRuntime::resolve_static_call_C(), where it returns get_c2i_entry() if is_interp_only_mode() is true.  However, there is still another problem.  By allowing JVMTI to suspend the thread during call setup, but reporting the frame as still in the caller instead of the callee, we confuse JVMTI into thinking that execution will resume in the caller instead of the callee.  We may want to restrict where we offer JVMTI suspend points, and not offer a JVMTI suspend point in SharedRuntime::resolve_static_call_C and friends at all. dl On 11/26/18 11:14 AM, Alex Menkov wrote: Hi all, Please review the fix for https://bugs.openjdk.java.net/browse/JDK-8195639 webrev: http://cr.openjdk.java.net/~amenkov/popframe009/webrev.01/ Description: The test suspends a thread, turns on single stepping and then calls PopFrame. SingleStep event is expected as soon as the thread is resumed and PopFrame is processed (so we have call stack with the depth 1 less than it was before PopFrame). Instead SingleStep event is received with much deeper call stack (and PopFrame processes wrong frame). Research shown that this is caused by missed deoptimization of the current frame. As far as I understand CompilationPolicy::event should handle the case when the thread has is_interp_only_mode() set, but TieredThresholdPolicy::event checks this only then CompLevel is CompLevel_none. CompilerRuntime always calls policy()->event with CompLevel == CompLevel_aot. The fix looks quite simple, but I'd appreciate feedback from runtime and compiler teams as I'm not sure I completely understand all the details of the "PopFrame dance". --alex