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

[coleen.phillimore at oracle.com]

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
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://mail.openjdk.java.net/pipermail/serviceability-dev/attachments/20191204/7a9cd97b/attachment.html>