RFR (M) 8212160: JVMTI agent crashes with "assert(_value != 0LL) failed: resolving NULL _value"

[coleen.phillimore at oracle.com]

On 12/5/19 8:05 AM, David Holmes wrote:
> Hi Coleen,
>
> On 5/12/2019 10:08 pm, coleen.phillimore at oracle.com wrote:
>>
>> Thanks Dan.  I moved the field.  For some reason I thought that class 
>> did more/different things than hold per-thread information.
>>
>> I've retested this version with tiers 2-6.
>>
>> incr webrev at 
>> http://cr.openjdk.java.net/~coleenp/2019/8212160.03.incr/webrev
>
> That relocation looks good to me!
>
> One minor nit:
>
> src/hotspot/share/code/nmethod.hpp
>
> +  void post_compiled_method_load_event(JvmtiThreadState* thread = NULL);
>
> parameter should be state not thread.

Ok yes, I'll fix it.  Thanks for the code review.
Coleen
>
> Thanks,
> David
> -----
>
>
>> full  webrev at 
>> http://cr.openjdk.java.net/~coleenp/2019/8212160.03/webrev
>>
>> Thanks to Serguei for offline discussion.
>>
>> Coleen
>>
>> On 12/4/19 7:40 PM, Daniel D. Daugherty wrote:
>>> Generally speaking, JVM/TI related things should be in JvmtiThreadState
>>> instead of directly in the Thread class. That way the extra space is 
>>> only
>>> consumed when JVM/TI is in use and only when a Thread does something 
>>> that
>>> requires a JvmtiThreadState to be created.
>>>
>>> Please reconsider moving _jvmti_event_queue.
>>>
>>> Dan
>>>
>>>
>>> On 12/4/19 6:06 PM, coleen.phillimore at oracle.com wrote:
>>>>
>>>> Hi Serguei,
>>>>
>>>> On 12/4/19 5:15 PM, serguei.spitsyn at oracle.com wrote:
>>>>> Hi Collen, (no problem)
>>>>>
>>>>> It looks good in general.
>>>>> Thank you a lot for sorting this out!
>>>>>
>>>>> Just a couple of comments.
>>>>>
>>>>>
>>>>> http://cr.openjdk.java.net/~coleenp/2019/8212160.01/webrev/src/hotspot/share/runtime/thread.hpp.frames.html 
>>>>>
>>>>> 1993 protected:
>>>>> 1994 // Jvmti Events that cannot be posted in their current context.
>>>>> 1995 // ServiceThread uses this to collect deferred events from 
>>>>> NonJava threads
>>>>> 1996 // that cannot post events.
>>>>> 1997 JvmtiDeferredEventQueue* _jvmti_event_queue;
>>>>>
>>>>> As David I also have a concern about footprint of having the 
>>>>> _jvmti_event_queue field in the Thread class.
>>>>> I'm thinking if it'd be better to move this field into the 
>>>>> JvmtiThreadState class.
>>>>> Please, see jvmti_thread_state() and 
>>>>> JvmtiThreadState::state_for(JavaThread *thread).
>>>>
>>>> The reason I have it directly in JavaThread is so that the GC 
>>>> oops_do and nmethods_do code can find it easily.  I like your idea 
>>>> of hiding it in jvmti but this doesn't seem good to have this code 
>>>> know about jvmtiThreadState, which seems to be a queue of Jvmti 
>>>> states.  I also don't want to have jvmtiThreadState to have to add 
>>>> an oops_do() or nmethods_do() either.
>>>>
>>>>>
>>>>>
>>>>> http://cr.openjdk.java.net/~coleenp/2019/8212160.01/webrev/src/hotspot/share/prims/jvmtiImpl.cpp.frames.html 
>>>>>
>>>>> 973 void JvmtiDeferredEvent::post(JvmtiEnv* env) {
>>>>> 974 assert(_type == TYPE_COMPILED_METHOD_LOAD, "only user of this 
>>>>> method");
>>>>> 975 nmethod* nm = _event_data.compiled_method_load;
>>>>> 976 JvmtiExport::post_compiled_method_load(env, nm);
>>>>> 977 }
>>>>>
>>>>> The JvmtiDeferredEvent::post name looks too generic as it posts 
>>>>> compiled load events only.
>>>>> Do you consider this function extended in the future to support 
>>>>> more event types?
>>>>>
>>>>
>>>> I don't envision an extension for this function but I do for 
>>>> JvmtiDeferredEventQueue::post().  I have a small enhancement that 
>>>> would handoff the entire queue to the ServiceThread and have it 
>>>> call post() to post all the events rather than one at a time.
>>>>
>>>> So I'll rename this one post_compiled_method_load_event() and leave 
>>>> the other post() as is for now.
>>>>
>>>> open webrev at 
>>>> http://cr.openjdk.java.net/~coleenp/2019/8212160.02.incr/webrev
>>>>
>>>> Thanks,
>>>> Coleen
>>>>
>>>>
>>>>>
>>>>> Thanks,
>>>>> Serguei
>>>>>
>>>>>
>>>>> On 11/26/19 06:22, coleen.phillimore at oracle.com wrote:
>>>>>> Summary: Add local deferred event list to thread to post events 
>>>>>> outside CodeCache_lock.
>>>>>>
>>>>>> This patch builds on the patch for JDK-8173361.  With this patch, 
>>>>>> I made the JvmtiDeferredEventQueue an instance class (not 
>>>>>> AllStatic) and have one per thread. The CodeBlob event that used 
>>>>>> to drop the CodeCache_lock and raced with the sweeper thread, 
>>>>>> adds the events it wants to post to its thread local list, and 
>>>>>> processes it outside the lock.  The list is walked in GC and by 
>>>>>> the sweeper to keep the nmethods from being unloaded and zombied, 
>>>>>> respectively.
>>>>>>
>>>>>> Also, the jmethod_id field in nmethod was only used as a boolean 
>>>>>> so don't create a jmethod_id until needed for 
>>>>>> post_compiled_method_unload.
>>>>>>
>>>>>> Ran hs tier1-8 on linux-x64-debug and the stress test that 
>>>>>> crashed in the original bug report.
>>>>>>
>>>>>> open webrev at 
>>>>>> http://cr.openjdk.java.net/~coleenp/2019/8212160.01/webrev
>>>>>> bug link https://bugs.openjdk.java.net/browse/JDK-8212160
>>>>>>
>>>>>> Thanks,
>>>>>> Coleen
>>>>>
>>>>
>>>
>>