gistfile1.diff

diff --git a/gc.c b/gc.c
index f4ec581..ae2a6d6 100644
--- a/gc.c
+++ b/gc.c
@@ -854,6 +854,9 @@ add_heap()
     if (heap_slots <= 0) heap_slots = heap_min_slots;
 
     while (p < pend) {
+	if (freelist == p) {
+		rb_bug("freelist == p (1)");
+	}
 	p->as.free.flags = 0;
 	p->as.free.next = freelist;
 	freelist = p;
@@ -1515,6 +1518,9 @@ finalize_list(p)
 	 * which can destroy copy-on-write semantics.
 	 */
 	if (!FL_TEST(p, FL_SINGLETON) && p->as.free.flags != 0) {
+	    if (freelist == p) {
+		rb_bug("freelist == p (2)");
+	    }
 	    p->as.free.flags = 0;
 	    p->as.free.next = freelist;
 	    rb_mark_table_remove(p);
@@ -1653,6 +1659,9 @@ gc_sweep()
 		if (need_call_final && FL_TEST(p, FL_FINALIZE)) {
 		    /* This object has a finalizer, so don't free it right now, but do it later. */
 		    rb_mark_table_heap_add(heap, p); /* remain marked */
+		    if (final_list == p) {
+			rb_bug("final_list == p (1)");
+		    }
 		    p->as.free.next = final_list;
 		    final_list = p;
 		}
@@ -1663,6 +1672,9 @@ gc_sweep()
 			    free_counts[obt]++;
 			}
 		    }
+		    if (freelist == p) {
+			rb_bug("freelist == p (3)");
+		    }
 		    /* Do not touch the fields if they don't have to be modified.
 		     * This is in order to preserve copy-on-write semantics.
 		     */
@@ -1737,6 +1749,9 @@ void
 rb_gc_force_recycle(p)
     VALUE p;
 {
+    if (freelist == p) {
+	rb_bug("freelist == p (4)");
+    }
     RANY(p)->as.free.flags = 0;
     RANY(p)->as.free.next = freelist;
     rb_mark_table_remove((RVALUE *) p);