Hi Daniil, You are right, there is a hole for this.
It can be easily fixed if the callbacks check phase at the beginning. But I don't think this would be simpler than your current fix. As I already mentioned, I'm Okay with the fix you have now. I'm still thinking on how to fix this on the JVMTI level. Thanks, Serguei On 3/20/19 16:35, Daniil Titov wrote:
Hi Serguei, I could be missing something but as I understood the suggested alternative approach was to not introduce the callbacksEnabled flag and instead just unregister other callbacks inside VMDeath callback. My concern was the case when one thread is on line 1302 (it is going to call a class loaded callback), while another thread just entered VMDeath callback. Without callbacksEnabled flag the first thread will enter the callback and wait on the raw monitor acquired by VMDeath callback thread, after that it will continue and call JVMTI API that might throw WRONG_PHASE error if by this time the second thread already returned from the VMDeath callback and changed the JVMTI phase. 1277 void JvmtiExport::post_class_load(JavaThread *thread, Klass* klass) { 1278 if (JvmtiEnv::get_phase() < JVMTI_PHASE_PRIMORDIAL) { 1279 return; 1280 } 1281 HandleMark hm(thread); 1282 1283 EVT_TRIG_TRACE(JVMTI_EVENT_CLASS_LOAD, ("[%s] Trg Class Load triggered", 1284 JvmtiTrace::safe_get_thread_name(thread))); 1285 JvmtiThreadState* state = thread->jvmti_thread_state(); 1286 if (state == NULL) { 1287 return; 1288 } 1289 JvmtiEnvThreadStateIterator it(state); 1290 for (JvmtiEnvThreadState* ets = it.first(); ets != NULL; ets = it.next(ets)) { 1291 if (ets->is_enabled(JVMTI_EVENT_CLASS_LOAD)) { 1292 JvmtiEnv *env = ets->get_env(); 1293 if (env->phase() == JVMTI_PHASE_PRIMORDIAL) { 1294 continue; 1295 } 1296 EVT_TRACE(JVMTI_EVENT_CLASS_LOAD, ("[%s] Evt Class Load sent %s", 1297 JvmtiTrace::safe_get_thread_name(thread), 1298 klass==NULL? "NULL" : klass->external_name() )); 1299 JvmtiClassEventMark jem(thread, klass); 1300 JvmtiJavaThreadEventTransition jet(thread); 1301 jvmtiEventClassLoad callback = env->callbacks()->ClassLoad; 1302 if (callback != NULL) { 1303 (*callback)(env->jvmti_external(), jem.jni_env(), jem.jni_thread(), jem.jni_class()); 1304 } 1305 } 1306 } 1307 } Thanks! --Daniil On 3/20/19, 3:40 PM, "serguei.spit...@oracle.com" <serguei.spit...@oracle.com> wrote: Hi Daniil,No chance for it if you lock a raw monitor in the event callbacks. Thanks,SergueiOn 3/20/19 14:58, Daniil Titov wrote:> Hi Serguei, > > I think that just disabling event notifications inside VMDeath callback still leaves a small window for VMDeath callback being called after the classload callback is called (or about being called) but before it enters a raw monitor. Thus I decided to follow your original suggestion and restore volatile modifier for callbacksEnabled. Please review a new version of the patch. > > Webrev: http://cr.openjdk.java.net/~dtitov/8218401/webrev.03/ > Bug : https://bugs.openjdk.java.net/browse/JDK-8218401 > > Thanks! > > Best regards, > Daniil > > > > From: <serguei.spit...@oracle.com> > Organization: Oracle Corporation > Date: Tuesday, March 19, 2019 at 7:17 PM > To: Daniil Titov <daniil.x.ti...@oracle.com>, OpenJDK Serviceability <serviceability-dev@openjdk.java.net>, Jean Christophe Beyler <jcbey...@google.com> > Subject: Re: 8218401: WRONG_PHASE: vmTestbase/nsk/jvmti test crash > > Hi Daniil, > > I'd keep the volatile modifier for callbacksEnabled to disable compiler optimizations. > Otherwise, looks good to me. > > > Another approach could be to disable event notifications in VMDeath callback with: > SetEventNotificationMode(JVMTI_DISABLE, JVMTI_EVENT_CLASS_LOAD, NULL); > SetEventNotificationMode(JVMTI_DISABLE, JVMTI_EVENT_BREAKPOINT, NULL); > . . . > > Thanks, > Serguei > > On 3/18/19 6:58 PM, Daniil Titov wrote: > Hi Serguei and JC, > > Please review a new version of the fix that locks a monitor across the callbacks, as Serguei suggested. > > Webrev: http://cr.openjdk.java.net/~dtitov/8218401/webrev.02/ > Bug: https://bugs.openjdk.java.net/browse/JDK-8218401 > > Thanks! > --Daniil > > > On 3/18/19, 9:47 AM, mailto:serguei.spit...@oracle.com mailto:serguei.spit...@oracle.com wrote: > > Hi Daniil, > > The JVMTI phase can change in the middle of callback work after the > check you added. > I'd suggest to lock a raw monitor across the callbacks to make them atomic. > > Thank you for taking care about this issue! > > Thanks, > Serguei > > > > On 3/15/19 16:08, Daniil Titov wrote: > > Please review the change that fixes 3 tests that intermittently fail with JVMTI_ERROR_WRONG_PHASE error. > > > > The problem here is that the callbacks these tests enable keep processing events and perform JVMTI calls after VM is terminated. The fix makes these test listen for VMDeath event and quick return from the callbacks after VMDeath event is received. > > > > Webrev: http://cr.openjdk.java.net/~dtitov/8218401/webrev.01/ > > Bug: https://bugs.openjdk.java.net/browse/JDK-8218401 > > > > Thanks! > > -Daniil > > > > > > > > > > > >
