skip marking for uninitialized imemo_env.

RUBY_INTERNAL_EVENT_NEWOBJ can expose uninitialized imemo_env
objects and marking it will cause critical error. This patch
skips marking on uninitialized imemo_env.

See: http://rubyci.s3.amazonaws.com/centos7/ruby-master/log/20210329T183003Z.fail.html.gz

Shortest repro-code is provided by mame-san.

1 files changed, 13 insertions, 0 deletions

diff --git a/test/objspace/test_objspace.rb b/test/objspace/test_objspace.rb
index 841a1e7c2a..1ccee02faa 100644
--- a/test/objspace/test_objspace.rb
+++ b/test/objspace/test_objspace.rb
@@ -243,6 +243,19 @@ class TestObjSpace < Test::Unit::TestCase
     GC.enable
   end
 
+  def test_trace_object_allocations_gc_stress
+    prev = GC.stress
+    GC.stress = true
+
+    ObjectSpace.trace_object_allocations{
+      proc{}
+    }
+
+    assert true # success
+  ensure
+    GC.stress = prev
+  end
+
   def test_dump_flags
     info = ObjectSpace.dump("foo".freeze)
     assert_match(/"wb_protected":true, "old":true/, info)