8197968: [Backout] JDK-8196883 G1RemSet::refine_card_concurrently doesn't need to check for cards in collection set

Reviewed-by: kbarrett

Author: tschatzl

src/hotspot/share/gc/g1/g1RemSet.cpp

@@ -586,6 +586,20 @@ void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
     return;
   }
 
+  // While we are processing RSet buffers during the collection, we
+  // actually don't want to scan any cards on the collection set,
+  // since we don't want to update remembered sets with entries that
+  // point into the collection set, given that live objects from the
+  // collection set are about to move and such entries will be stale
+  // very soon. This change also deals with a reliability issue which
+  // involves scanning a card in the collection set and coming across
+  // an array that was being chunked and looking malformed. Note,
+  // however, that if evacuation fails, we have to scan any objects
+  // that were not moved and create any missing entries.
+  if (r->in_collection_set()) {
+    return;
+  }
+
   // The result from the hot card cache insert call is either:
   //   * pointer to the current card
   //     (implying that the current card is not 'hot'),
@@ -610,7 +624,8 @@ void G1RemSet::refine_card_concurrently(jbyte* card_ptr,
 
       // Check whether the region formerly in the cache should be
       // ignored, as discussed earlier for the original card.  The
-      // region could have been freed while in the cache.
+      // region could have been freed while in the cache.  The cset is
+      // not relevant here, since we're in concurrent phase.
       if (!r->is_old_or_humongous()) {
         return;
       }