8240693: Sweeper should not examine dying metadata in is_unloading() …

…nmethod during static call stub cleaning

Reviewed-by: kvn, coleenp, pliden

src/hotspot/share/code/codeCache.cpp

@@ -1073,8 +1073,8 @@ void CodeCache::old_nmethods_do(MetadataClosure* f) {
     length = old_compiled_method_table->length();
     for (int i = 0; i < length; i++) {
       CompiledMethod* cm = old_compiled_method_table->at(i);
-      // Only walk alive nmethods, the dead ones will get removed by the sweeper.
-      if (cm->is_alive()) {
+      // Only walk alive nmethods, the dead ones will get removed by the sweeper or GC.
+      if (cm->is_alive() && !cm->is_unloading()) {
         old_compiled_method_table->at(i)->metadata_do(f);
       }
     }

src/hotspot/share/code/compiledMethod.cpp

@@ -642,6 +642,11 @@ bool CompiledMethod::cleanup_inline_caches_impl(bool unloading_occurred, bool cl
         continue;
       }
       is_in_static_stub = false;
+      if (is_unloading()) {
+        // If the nmethod itself is dying, then it may point at dead metadata.
+        // Nobody should follow that metadata; it is strictly unsafe.
+        continue;
+      }
       metadata_Relocation* r = iter.metadata_reloc();
       Metadata* md = r->metadata_value();
       if (md != NULL && md->is_method()) {