8309663: test fails "assert(check_alignment(result)) failed: address not aligned: 0x00000008baadbabe"

Reviewed-by: sspitsyn, eosterlund

Author: Alex Menkov

src/hotspot/share/prims/jvmtiTagMap.cpp

@@ -2320,7 +2320,10 @@ bool StackRefCollector::do_frame(vframe* vf) {
       // Follow oops from compiled nmethod.
       if (jvf->cb() != nullptr && jvf->cb()->is_nmethod()) {
         _blk->set_context(_thread_tag, _tid, _depth, method);
-        jvf->cb()->as_nmethod()->oops_do(_blk);
+        // Need to apply load barriers for unmounted vthreads.
+        nmethod* nm = jvf->cb()->as_nmethod();
+        nm->run_nmethod_entry_barrier();
+        nm->oops_do(_blk);
         if (_blk->stopped()) {
           return false;
         }

test/hotspot/jtreg/ProblemList-zgc.txt

@@ -45,4 +45,3 @@ vmTestbase/gc/gctests/MemoryEaterMT/MemoryEaterMT.java        8289582   windows-
 
 vmTestbase/nsk/monitoring/MemoryPoolMBean/isCollectionUsageThresholdExceeded/isexceeded002/TestDescription.java 8298302 generic-all
 vmTestbase/nsk/sysdict/vm/stress/chain/chain007/chain007.java 8298991 linux-x64
-serviceability/jvmti/vthread/FollowReferences/VThreadStackRefTest.java#default 8309663 linux-x64